IONIS PHARMACEUTICALS INC

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

1. Organization and Significant Accounting Policies

Basis of Presentation

In our consolidated financial statements we included the accounts of Ionis Pharmaceuticals, Inc. and the consolidated results of our wholly owned subsidiary, Akcea Therapeutics, Inc. and its wholly owned subsidiaries (“we”, “us” or “our”).

Organization and Business Activity

We incorporated in California on January 10, 1989. In conjunction with our IPO, we reorganized as a Delaware corporation in April 1991. We were organized principally to develop human therapeutic medicines using antisense technology. In December 2015, we changed our name from Isis Pharmaceuticals, Inc. to Ionis Pharmaceuticals, Inc.

Use of Estimates

We prepare our consolidated financial statements in conformity with accounting principles generally accepted in the United States, or U.S., that require us to make estimates and assumptions that affect the amounts reported in our consolidated financial statements and accompanying notes. Actual results could differ from our estimates.

Revenue Recognition

We generally recognize revenue when we have satisfied all contractual obligations and are reasonably assured of collecting the resulting receivable. We are often entitled to bill our customers and receive payment from our customers in advance of recognizing the revenue. In the instances in which we have received payment from our customers in advance of recognizing revenue, we include the amounts within deferred revenue in our consolidated balance sheets.

At contract inception, we analyze our collaboration arrangements to assess whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities and therefore within the scope of ASC Topic 808, Collaborative Arrangements, or ASC 808. ASC 808 does not address the recognition and measurement of collaborative arrangements and instead refers companies to use other authoritative accounting literature. For collaboration arrangements within the scope of ASC 808 that contain multiple elements, wefirst determine which elements of the collaboration reflect a vendor-customer relationship and therefore are within the scope of ASC 606, Revenue from Contracts with Customers. When we determine elements of a collaboration do not reflect a vendor-customer relationship, we consistently apply the reasonable and rational policy election we made by analogizing to authoritative accounting literature.

We evaluate the income statement classification for presentation of amounts due from or owed to other participants associated with multiple activities in a collaboration arrangement based on the nature of each separate activity. For example, in our WAINUA collaboration with AstraZeneca, we recognize funding received from AstraZeneca for co-development activities as revenue; while we recognize cost sharing payments to and from AstraZeneca associated with co-commercialization activities and co-medical affairs activities as selling, general and administrative, or SG&A, expense and research and development, or R&D, expense, respectively.

Steps to Recognize Revenue

For elements of our contractual relationships that we account for under ASC 606, we use a five-step process to determine the amount of revenue we should recognize and when we should recognize it. The five-step process is as follows:

Accounting rules require us to first determine if we have a contract with our partner, including confirming that we have met each of the following criteria:

We next identify our performance obligations, which represent the distinct goods and services we are required to provide under the contract.

We may enter into a collaboration agreement in which we provide our partner with an option to license a medicine in the future. We may also provide our partner with an option to request that we provide additional goods or services in the future, such as active pharmaceutical ingredient, or API. We evaluate whether these options are material rights at the inception of the agreement. If we determine an option is a material right, we will consider the option a separate performance obligation. When a partner exercises its option to license a medicine that was not previously determined to be a material right at the inception of the agreement or requests additional goods or services, then we identify a new performance obligation for that item.

In some cases, we deliver a license at the start of an agreement. If we determine that our partner has full use of the license and we do not have any additional material performance obligations related to the license after delivery, then we consider the license to be a separate performance obligation.

We then determine the transaction price by reviewing the amount of consideration we are eligible to earn under the collaboration agreement, including any variable consideration. Under our collaboration agreements, consideration typically includes fixed consideration in the form of an upfront payment and variable consideration in the form of potential milestone payments, license fees and royalties. At the start of an agreement, our transaction price usually consists of only the upfront payment. We do not typically include any payments we may receive in the future in our initial transaction price because the payments are not probable and are contingent on certain future events. We reassess the total transaction price at each reporting period to determine if we should include additional payments in the transaction price.

Milestone payments are our most common type of variable consideration. We recognize milestone payments using the most likely amount method because we will either receive the milestone payment or we will not, which makes the potential milestone payment a binary event. The most likely amount method requires us to determine the likelihood of earning the milestone payment. We include a milestone payment in the transaction price once it is probable that we will achieve the milestone event. Most often, we do not consider our milestone payments probable until we or our partner achieve the milestone event because the majority of our milestone payments are contingent upon events that are not within our control and/ or are usually based on scientific progress which is inherently uncertain.

Next, we allocate the transaction price to each of our performance obligations. When we have to allocate the transaction price to more thanone performance obligation, we make estimates of the relative stand-alone selling price of each performance obligation because we do not typically sell our goods or services on a stand-alone basis. We then allocate the transaction price to each performance obligation based on the relative stand-alone selling price. We do not reallocate the transaction price after the start of an agreement to reflect subsequent changes in stand-alone selling prices.

We may engage athird party, independent valuation specialist to assist us with determining a stand-alone selling price for collaborations in which we deliver a license at the start of an agreement. We estimate the stand-alone selling price of these licenses using valuation methodologies, such as the relief from royalty method. Under this method, we estimate the amount of income, net of taxes, for the license. We then discount the projected income to present value. The significant inputs we use to determine the projected income of a license could include:

We typically estimate the selling price of R&D services by using our internal estimates of the cost to perform the specific services. The significant inputs we use to determine the selling price of our R&D services include:

For purposes of determining the stand-alone selling price of the R&D services we perform and the API we will deliver, accounting guidance requires us to include a markup for a reasonable profit margin.

We recognize revenue inone oftwo ways, over time or at a point in time. We recognize revenue over time when we are executing on our performance obligation over time and our partner receives benefit over time. For example, we recognize revenue over time when we provide R&D services. We recognize revenue at a point in time when our partner receives full use of an item at a specific point in time. For example, we recognize revenue at a point in time when we deliver a license or API to a partner.

For R&D services that we recognize over time, we measure our progress using an input method. The input methods we use are based on the effort we expend or costs we incur toward the satisfaction of our performance obligation. We estimate the amount of effort we expend, including the time we estimate it will take us to complete the activities, or costs we incur in a given period, relative to the estimated total effort or costs to satisfy the performance obligation. This results in a percentage that we multiply by the transaction price to determine the amount of revenue we recognize each period. This approach requires us to make numerous estimates and use significant judgement. If our estimates or judgements change over the course of the collaboration, they may affect the timing and amount of revenue that we recognize in the current and future periods.

We recognize royalty revenue in the period in which the counterparty sells the related product and recognizes the related revenue, which in certain cases may require us to estimate our royalty revenue.

Under our distribution agreements with Swedish Orphan Biovitrum AB, or Sobi, we concluded that our performance obligation is to provide services to Sobi over the term of the agreement, which includes supplying finished goods inventory to Sobi. We are also responsible for maintaining the marketing authorization for TEGSEDI and WAYLIVRA in major markets and for leading the global commercial strategy for each medicine. We view this performance obligation as a series of distinct activities that are substantially the same. Therefore, we recognize as revenue the price Sobi pays us for the inventory when we deliver the finished goods inventory to Sobi. We also recognize distribution fee revenue based on Sobi’s net sales of TEGSEDI and WAYLIVRA. Under our agreements with Sobi, Sobi does not generally have a right of return.

Amendments to Agreements

From time to time we amend our collaboration agreements. When this occurs, we are required to assess the following items to determine the accounting for the amendment:

If we conclude the goods and/or services in the amendment are distinct from the performance obligations in the original agreement and at a stand-alone selling price, we account for the amendment as a separate agreement. If we conclude the goods and/or services are not distinct and are sold at a stand-alone selling price, we then assess whether the remaining goods or services are distinct from those already provided. If the goods and/or services are distinct from what we have already provided, then we allocate the remaining transaction price from the original agreement and the additional transaction price from the amendment to the remaining goods and/or services. If the goods and/or services are not distinct from what we have already provided, we update the transaction price for our single performance obligation and recognize any change in our estimated revenue as a cumulative-effect adjustment.

Multiple agreements

From time to time, we may enter into separate agreements at or near the same time with the same partner. We evaluate such agreements to determine whether we should account for them individually as distinct arrangements or whether the separate agreements should be combined and accounted for together. We evaluate the following to determine the accounting for the agreements:

Our evaluation involves significant judgment to determine whether a group of agreements might be so closely related that accounting guidance requires us to account for them as a combined arrangement.

Refer to Note 4, Collaborative Arrangements and Licensing Agreements, for further discussion of our 2018 Strategic Neurology collaboration with Biogen that included multiple agreements which we negotiated concurrently and in contemplation of one another.

Contracts Receivable

Our contracts receivable balance represents the amounts we have billed our partners or customers and that are due to us unconditionally for goods we have delivered or services we have performed. When we bill our partners or customers with payment terms based on the passage of time, we consider the contracts receivable to be unconditional. We typically receive payment within onequarter of billing our partner or customer.

As of December 31, 2023, approximately 87.8 percent of our contracts receivables were fromone significant customer. As of December 31, 2022, approximately 82.5 percent of our contracts receivables were fromone significant customer.

Unbilled SPINRAZA Royalties

Our unbilled SPINRAZA royalties represent our right to receive consideration from Biogen in advance of when we are eligible to bill Biogen for SPINRAZA royalties. We include these unbilled amounts in other current assets in our consolidated balance sheets.

Deferred Revenue

We are often entitled to bill our customers and receive payment from our customers in advance of our obligation to provide services or transfer goods to our partners. In these instances, we include the amounts in deferred revenue in our consolidated balance sheets. During the years ended December 31, 2023 and 2022, we recognized $78.2 million and $73.5 million of revenue from amounts that were in our beginning deferred revenue balance for each respective period. For further discussion, refer to our revenue recognition policy above.

Cost of Sales

Our cost of sales is comprised of costs related to our commercial revenue, including manufacturing costs, transportation and freight costs and indirect overhead costs associated with the manufacturing and distribution of our products. We also may include certain period costs related to manufacturing services and inventory adjustments in cost of sales.

Research, Development and Patent Expenses

Our research, development and patent expenses include wages, benefits, facilities, supplies, external services, clinical trial and manufacturing costs, patents and other expenses that are directly related to our R&D operations. We expense R&D costs as we incur them. When we make payments for R&D services prior to the services being rendered, we record those amounts as prepaid assets in our consolidated balance sheets and we expense them as the services are provided. A portion of the costs included in R&D expenses are costs associated with our partner agreements. In 2023, 2022 and 2021, patent expenses were $4.3 million, $4.7 million and $5.3 million, respectively.

Income Taxes

We account for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in our financial statements or tax returns. In addition, deferred tax assets are recorded for the future benefit of utilizing net operating losses and research and development credit carryforwards. We record a valuation allowance when necessary to reduce our net deferred tax assets to the amount expected to be realized.

We apply the authoritative accounting guidance prescribing a threshold and measurement attribute for the financial recognition and measurement of a tax position taken or expected to be taken in a tax return. We recognize liabilities for uncertain tax positions based on a two-step process. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained on audit, including resolution of related appeals or litigation processes, if any. The second step requires us to estimate and measure the tax benefit as the largest amount that is more than 50 percent likely to be realized upon ultimate settlement.

We are required to use significant judgment in evaluating our uncertain tax positions and determining our provision for income taxes. Although we believe our reserves are reasonable, we can provide no assurance that the final tax outcome of these matters will not be different from that which we have reflected in our historical income tax provisions and accruals. We adjust these reserves for changing facts and circumstances, such as the closing of a tax audit or the refinement of an estimate. To the extent that the final tax outcome of these matters is different than the amounts recorded, such differences may impact the provision for income taxes in the period in which we make such determination.

We are also required to use significant judgment in determining any valuation allowance recorded against our deferred tax assets. In assessing the need for a valuation allowance, we consider all available evidence, including scheduled reversal of deferred tax liabilities, past operating results, the feasibility of tax planning strategies and estimates of future taxable income. We base our estimates of future taxable income on assumptions that are consistent with our plans. The assumptions we use represent our best estimates and involve inherent uncertainties and the application of our judgment. Should actual amounts differ from our estimates, the amount of our tax expense and liabilities we recognize could be materially impacted. We record a valuation allowance to reduce the balance of our net deferred tax assets to the amount we believe is more-likely-than-not to be realized.

Basic and Diluted Net Loss per Share

Basic net loss per share

We compute basic net loss per share by dividing our net loss by our weighted-average number of common shares outstanding during the period.

Diluted net loss per share

For the years ended December 31, 2023, 2022 and 2021, we incurred a net loss; therefore, we did not include dilutive common equivalent shares in the computation of diluted net loss per share because the effect would have been anti-dilutive. Common stock from the following would have had an anti-dilutive effect on net loss per share:

For the year ended December 31, 2023, common stock underlying the 1.75 percent convertible senior notes, or 1.75% Notes, would also have had an anti-dilutive effect on net loss per share.

Additionally as of December 31, 2023, 2022 and 2021, we had warrants related to our 0% Notes and 0.125% Notes outstanding. We will include the shares issuable under these warrants in our calculation of diluted earnings per share when the average market price per share of our common stock for the reporting period exceeds the strike price of the warrants.

Stock-Based Compensation Expense

We measure stock-based compensation expense for equity-classified awards, principally related to stock options, RSUs, PRSUs and stock purchase rights under our ESPP based on the estimated fair value of the award on the date of grant. We recognize the value of the portion of the award that we ultimately expect to vest as stock-based compensation expense over the requisite service period in our consolidated statements of operations. We reduce stock-based compensation expense for estimated forfeitures at the time of grant and revise in subsequent periods if actual forfeitures differ from those estimates.

We recognize compensation expense for stock options granted, RSUs, PRSUs and stock purchase rights under the ESPP using the accelerated multiple-option approach. Under the accelerated multiple-option approach (also known as the graded-vesting method), we recognize compensation expense over the requisite service period for each separately vesting tranche of the award as though the award were in substance multiple awards, which results in the expense being front-loaded over the vesting period.

Stock Options and Stock Purchase Rights:

We use the Black-Scholes model to estimate the fair value of stock options granted and stock purchase rights under our ESPP. On the grant date, we use our stock price and assumptions regarding a number of variables to determine the estimated fair value of stock-based payment awards. These variables include, but are not limited to, our expected stock price volatility over the term of the awards, and actual and projected employee stock option exercise behaviors. The expected term of stock options granted represents the period of time that we expect them to be outstanding. Historically, we estimated the expected term of options granted based on historical exercise patterns. In 2021, our Compensation Committee approved an amendment to the 2011 Equity Incentive Plan, or 2011 Plan, and the 2020 Equity Incentive Plan, or 2020 Plan, that increased the contractual term of stock options granted under these plans from seven years toten years for stock options granted on January 1, 2022 and thereafter. We determined that we are unable to rely on our historical exercise data as a basis for estimating the expected life of stock options granted to employees following this change because the contractual term changed and we have no other means to reasonably estimate future exercise behavior. We therefore used the simplified method for determining the expected life of stock options granted to employees in the years ended December 31, 2023 and 2022. Under the simplified method, we calculate the expected term as the average of the time-to-vesting and the contractual life of the options. As we gain additional historical information, we will transition to calculating our expected term based on our historical exercise patterns.

RSU’s:

The fair value of RSUs is based on the market price of our common stock on the date of grant. The RSUs we have granted to employees vest annually over afour-year period. The RSUs we granted to our board of directors prior to June 2020 vest annually over afour-year period. RSUs we granted to our board of directors after June 2020 fully vest afterone year.

PRSU’s:

Beginning in 2020, we added PRSU awards to the compensation for our Chief Executive Officer, Dr. Brett Monia. Beginning in 2022, we added PRSU awards to the compensation for our other Section 16 officers. Under the terms of the PRSUs we granted in 2020 through 2022, one third of the PRSUs may vest at the end ofthree separate performance periods spread over thethree years following the date of grant (i.e., theone-year period commencing on the date of grant and ending on the first anniversary of the date of grant; thetwo-year period commencing on the date of grant and ending on the second anniversary of the date of grant; and thethree-year period commencing on the date of grant and ending on the third anniversary of the date of grant) based on our relative total shareholder return, or TSR, as compared to a peer group of companies, and as measured, in each case, at the end of the applicable performance period. Under the terms of the grantsno number of PRSUs is guaranteed to vest and the actual number of PRSUs that will vest at the end of each performance period may be anywhere from zero to 150 percent of the target number depending on our relative TSR. These PRSU awards also included an alternative three-year payout mechanism, or the Alternative Calculation, under which we must calculate an alternative payout at the end of the final three-year measurement period assuming the only measurement period for all shares under the award was thethree-year period. If the Alternative Calculation is greater than payouts under the sum of thethree years, then such PRSU award will pay out to achieve the number of shares payable under the Alternative Calculation.

Under the terms of the PRSUs we granted in 2023,100 percent of the PRSUs may vest at the end of thethree-year performance period based on our relative TSR as compared to a peer group of companies and as measured at the end of the performance period. Under the terms of the grants, no number of PRSUs is guaranteed to vest and the actual number of PRSUs that will vest at the end of each performance period may be anywhere from zero to 200 percent of the target number depending on our relative TSR.

We determined the fair value of the PRSUs using a Monte Carlo model because the performance target is based on our relative TSR, which represents a market condition. We are recognizing the grant date fair value of these awards as stock-based compensation expense using the accelerated multiple-option approach over the vesting period.

Refer to Note 8, Stockholders’ Equity, for additional information regarding our stock-based compensation plans.

Concentration of Credit Risk

Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash equivalents, short-term investments and receivables. We place our cash equivalents and short-term investments with reputable financial institutions. We primarily invest our excess cash in commercial paper and debt instruments of the U.S. Treasury, financial institutions, corporations, and U.S. government agencies with strong credit ratings and an investment grade rating at or above A-1, P-1 or F-1 by Moody’s, Standard & Poor’s, or S&P, or Fitch, respectively. We have established guidelines relative to diversification and maturities that maintain safety and liquidity. We periodically review and modify these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity.

Fair Value Measurements

We have estimated the fair value of our financial instruments. The amounts reported for cash, accounts receivable, accounts payable and accrued expenses approximate the fair value because of their short maturities. We report our investment securities at their estimated fair value based on quoted market prices for identical or similar instruments.

We use a three-tier fair value hierarchy to prioritize the inputs used in our fair value measurements. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets for identical assets, which includes our money market funds and treasury securities classified as available-for-sale securities and our investment in equity securities in publicly traded biotechnology companies; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable, which includes our fixed income securities and commercial paper classified as available-for-sale securities; and Level 3, defined as unobservable inputs in which little or no market data exists, therefore requiring us to develop our own assumptions. We classify most of our securities as Level 2. We obtain the fair value of our Level 2 investments from our custodian bank or from a professional pricing service. We validate the fair value of our Level 2 investments by understanding the pricing model used by the custodian banks or professional pricing service provider and comparing that fair value to the fair value based on observable market prices.

Cash, Cash Equivalents and Investments

We consider all liquid investments with maturities of three months or less when we purchase them to be cash equivalents. Our short-term investments have initial maturities of greater than three months from date of purchase. We classify our short-term debt investments as “available-for-sale” and carry them at fair market value based upon prices on the last day of the fiscal period for identical or similar items. We record unrealized gains and losses on debt securities as a separate component of comprehensive income (loss) and include net realized gains and losses in gain (loss) on investments in our consolidated statements of operations. We use the specific identification method to determine the cost of securities sold.

We also have equity investments of less than 20 percent ownership in public and private biotechnology companies that we received as part of a technology license or partner agreement. At December 31, 2023, we held equity investments inthree publicly traded companies andseven privately held companies.

We are required to measure and record our equity investments at fair value and to recognize the changes in fair value in our consolidated statements of operations. We account for our equity investments in publicly traded companies at their listed stock price. We account for our equity investments in privately held companies at their cost minus impairments, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer.

Inventories

We reflect our inventory in our consolidated balance sheets at the lower of cost or net realizable value under the first-in, first-out method, or FIFO. We capitalize the costs of raw materials that we purchase for use in producing our medicines because until we use these raw materials, they have alternative future uses, which we refer to as clinical raw materials. We include in inventory raw material costs for medicines that we manufacture for our partners under contractual terms and that we use primarily in our clinical development activities and drug products. We can use each of our raw materials in multiple products and, as a result, each raw material has future economic value independent of the development status of any single medicine. For example, if one of our medicines failed, we could use the raw materials for that medicine to manufacture our other medicines. We expense these costs as R&D expenses when we begin to manufacture API for a particular medicine if the medicine has not been approved for marketing by a regulatory agency. Our raw materials- commercial inventory includes API for our commercial medicines. We capitalize material, labor and overhead costs as part of our raw materials- commercial inventory.

We review our inventory periodically and reduce the carrying value of items we consider to be slow moving or obsolete to their estimated net realizable value based on forecasted demand compared to quantities on hand. We consider several factors in estimating the net realizable value, including shelf life of our inventory, alternative uses for our medicines in development and historical write-offs.

Property, Plant and Equipment

We carry our property, plant and equipment at cost and depreciate it on the straight-line method over its estimated useful life, which we determine as the following (in years):

We depreciate our leasehold improvements using the shorter of the estimated useful life or remaining lease term. We evaluate long-lived assets, which include property, plant and equipment, for impairment on at least a quarterly basis and whenever events or changes in circumstances indicate that we may not be able to recover the carrying amount of such assets.

Accrued Liabilities

We have numerous medicines in preclinical studies and/or clinical trials at clinical sites throughout the world. On at least a quarterly basis, we estimate our liability for preclinical and clinical development costs we have incurred and services that we have received but for which we have not yet been billed and maintain an accrual to cover these costs. These costs primarily relate to third-party clinical management costs, laboratory and analysis costs, toxicology studies and investigator grants. We estimate our liability using assumptions about study and patient activities and the related expected expenses for those activities determined based on the contracted fees with our service providers. The assumptions we use represent our best estimates of the activity and expenses at the time of our accrual and involve inherent uncertainties and the application of our judgment. Upon settlement, these costs may differ materially from the amounts accrued in our consolidated financial statements. Our historical accrual estimates have not been materially different from our actual amounts.

Convertible Debt

We account for each of our convertible debt instruments as a single unit of accounting, a liability, because we concluded that the conversion features do not require bifurcation as a derivative under ASC 815-15 and we did not issue our convertible debt instruments at a substantial premium. We record debt issuance costs as contra-liabilities in our consolidated balance sheets at issuance and amortize them over the contractual term of the convertible debt instrument using the effective interest rate. The balances of our convertible senior notes presented in our consolidated balance sheets represent the principal balance of each convertible debt instrument less debt issuance costs.

As of December 31, 2023, we hadthree outstanding convertible senior notes, our 1.75% Notes, which mature in June 2028, our 0% Notes, which mature in April 2026, and our 0.125% Notes, which mature in December 2024. Refer to Note 7, Long-Term Obligations and Commitments, for further details on our convertible senior notes.

Call Spread

In conjunction with the issuance of our 0% Notes and 0.125% Notes in April 2021 and December 2019, respectively, we entered into call spread transactions, which were comprised of purchasing note hedges and selling warrants. We account for the note hedges and warrants as separate freestanding financial instruments and treat each instrument as a separate unit of accounting. We determined that the note hedges and warrants do not meet the definition of a liability using the guidance contained in ASC Topic 480; therefore, we account for the note hedges and warrants using the Derivatives and Hedging – Contracts in Entity’s Own Equity accounting guidance contained in ASC Topic 815. We determined that the note hedges and warrants meet the definition of a derivative, are indexed to our stock and meet the criteria to be classified in shareholders’ equity. We recorded the aggregate amount paid for the note hedges and the aggregate amount received for the warrants as additional paid-in capital in our consolidated balance sheets. We reassess our ability to continue to classify the note hedges and warrants in shareholders’ equity at each reporting period.

Liability Related to Sale of Future Royalties

In January 2023, we entered into a royalty purchase agreement with Royalty Pharma Investments, or Royalty Pharma, to monetize a portion of our future SPINRAZA and pelacarsen royalties we are entitled to under our arrangements with Biogen and Novartis, respectively. Refer to Note 7, Long-Term Obligations and Commitments, for further details on the agreement.

Under our agreement with Royalty Pharma, we record upfront payments and milestone payments we receive from the sale of future royalties as a liability, net of transaction costs. We record royalty payments made to Royalty Pharma as a reduction of the liability or accrued interest and amortize the transaction costs over the estimated life of the royalty stream. We account for the associated interest expense under the effective interest rate method, while continuing to recognize the full amount of royalty revenue in the period in which the counterparty sells the related product and recognizes the related revenue.

We calculate the liability related to the sale of future royalties, effective interest rate and the related interest expense using our current estimate of anticipated future royalty payments under the arrangement, which we periodically reassess based on internal projections and information from our partners who are responsible for commercializing the medicines. If there is a material change in our estimate, we will prospectively adjust the effective interest rate and the related interest expense.

Leases

We determine if an arrangement contains a lease at inception. We currently only have operating leases. We recognize a right-of-use operating lease asset and associated short- and long-term operating lease liability in our consolidated balance sheets for operating leases greater than one year. Our right-of-use assets represent our right to use an underlying asset for the lease term and our lease liabilities represent our obligation to make lease payments arising from the lease arrangement. We recognize our right-of-use operating lease assets and lease liabilities based on the present value of the future minimum lease payments we will pay over the lease term. We determine the lease term at the inception of each lease, and in certain cases our lease term could include renewal options if we conclude we are reasonably certain to exercise the renewal option. When we exercise a lease option that was not previously included in the initial lease term, we reassess our right-of-use asset and lease liabilities for the new lease term.

As our leases do not provide an interest rate implicit in the lease, we use our incremental borrowing rate, based on the information available as of the lease inception date or at the lease option extension date in determining the present value of future payments. We recognize rent expense for our minimum lease payments on a straight-line basis over the expected term of our lease. Our leases do not include material variable or contingent lease payments. We recognize period expenses, such as common area maintenance expenses, in the period we incur the expense.

Segment Information

We operate as a single segment, Ionis operations, because our chief decision maker reviews operating results on an aggregate basis and manages our operations as asingle operating segment.

Recently Issued Accounting Standards

In November 2023, the Financial Accounting Standards Board, or FASB, issued updated guidance on segment reporting. The guidance requires public companies with a single reportable segment to provide all disclosures required under ASC 280, Segment Reporting. In addition, the guidance requires public companies to include in interim reports all disclosures related to a reportable segment's profit or loss and assets that are currently required in annual reports. This update is effective for annual periods beginning after December 15, 2023 and interim periods beginning after December 15, 2024. The guidance is applied on a retrospective basis for all periods presented in the financial statements, unless it is impracticable. Early adoption of this guidance is permitted. We currently plan to adopt the annual reporting requirements in our 2024 Annual Report on Form 10-K. We plan to adopt the interim reporting requirements in our Quarterly Report on Form 10-Q in the first quarter of 2025.

In December 2023, the FASB issued updated guidance on income tax disclosures. The new guidance requires companies to provide additional disaggregation of information related to the income tax rate reconciliation and income tax payments. In addition, the guidance eliminates certain existing disclosure requirements related to uncertain tax positions and unrecognized deferred tax liabilities. This update is effective for annual periods beginning after December 15, 2024. Early adoption of this guidance is permitted. We currently plan to adopt this guidance in our 2025 Annual Report on Form 10-K.

We do not expect any other recently issued accounting standards to have a material impact to our financial results.

2. Supplemental Financial Data

Inventories

Our inventory consisted of the following (in thousands):

Property, Plant and Equipment

Our property, plant and equipment consisted of the following (in thousands):

Accrued Liabilities

Our accrued liabilities consisted of the following (in thousands):

3. Revenues

During the years ended December 31,2023,2022 and 2021, our revenues were comprised of the following (in thousands):

Revenue Sources

The following are sources of revenue and when we typically recognize revenue.

Commercial Revenue: SPINRAZA royalties and Licensing and other royalty revenue

We earn commercial revenue primarily in the form of royalty payments on net sales of SPINRAZA. We earn royalty revenue on net sales of QALSODY which is included in Licensing and other royalty revenue.

Commercial Revenue: TEGSEDI and WAYLIVRA revenue, net

We earn commercial revenue from TEGSEDI and WAYLIVRA sales under our distribution agreements with Sobi. In addition, we receive royalties from PTC Therapeutics International Limited, or PTC, for TEGSEDI and WAYLIVRA sales. Refer to Note 4, Collaborative Arrangements and Licensing Agreements, for details on our commercialization partnerships with Sobi and PTC.

Research and development revenue under collaboration agreements

We enter into collaboration agreements to license and sell our technology on an exclusive or non-exclusive basis. Our collaboration agreements typically contain multiple elements, or performance obligations, including technology licenses or options to obtain technology licenses, R&D services and manufacturing services.

Upfront payments: When we enter into a collaboration agreement and receive an upfront payment, we typically record the entire upfront payment as deferred revenue if our only performance obligation is for R&D services we will provide in the future. We amortize the upfront payment into revenue as we perform the R&D services.

Milestone payments: We include variable consideration in the transaction price when it is probable. We typically include milestone payments for R&D services in the transaction price when they are achieved. We include these milestone payments when they are achieved because typically there is considerable uncertainty in the research and development processes that trigger these payments. Similarly, we include approval milestone payments in the transaction price once the medicine is approved by the applicable regulatory agency. We will recognize sales-based milestone payments in the period in which we achieve the milestone under the sales-based royalty exception allowed under accounting rules.

We recognize milestone payments that relate to an ongoing performance obligation over our period of performance. For example, when we achieve a milestone payment from a partner for advancing a clinical study under a collaboration agreement, we add the milestone payment to the transaction price if the milestone relates to an ongoing R&D services performance obligation and recognize revenue related to the milestone payment over our estimated period of performance. If we have partially completed our performance obligation, then we record a cumulative-effect adjustment in the period we add the milestone payment to the transaction price.

Conversely, we recognize in full those milestone payments that we earn based on our partners’ activities when our partner achieves the milestone event and we do not have a performance obligation.

License fees: We recognize as revenue the total amount we determine to be the relative stand-alone selling price of a license when we deliver the license to our partner who has full use of the license and we do not have any additional performance obligations related to the license after delivery.

Sublicense fees: We recognize sublicense fee revenue in the period in which a party, who has already licensed our technology, further licenses the technology to another party because we do not have any performance obligations related to the sublicense.

WAINUA (Eplontersen) Collaboration with AstraZeneca

In December 2021, we entered into a joint development and commercialization agreement with AstraZeneca to develop and commercialize WAINUA for the treatment of transthyretin amyloidosis, or ATTR. We jointly developed and are preparing to commercialize WAINUA with AstraZeneca in the U.S. We initially granted AstraZeneca exclusive rights to commercialize WAINUA outside the U.S., except for certain Latin American countries. In July 2023, we expanded those rights to include Latin America. Under the terms of the agreement, we received a $200 million upfront payment in 2021.

We evaluated our WAINUA collaboration under ASC 808 and identified four material components: (i) the license we granted to AstraZeneca in 2021, (ii) the co-development activities that we and AstraZeneca are performing, (iii) the co-commercialization activities that we and AstraZeneca are performing and (iv) the co-medical affairs activities that we and AstraZeneca are performing.

We determined that we had a vendor-customer relationship within the scope of ASC 606 for the license we granted to AstraZeneca and as a result we hadone performance obligation. For our sole performance obligation, we determined the transaction price was the $200 million upfront payment we received. We recognized the upfront payment in full in 2021 because we did not have any remaining performance obligations after we delivered the license to AstraZeneca.

We also concluded that the co-development activities, the co-commercialization activities and the co-medical affairs activities are within the scope of ASC 808 because we and AstraZeneca are active participants exposed to the risks and benefits of the activities under the collaboration and therefore do not have a vendor-customer relationship. AstraZeneca is currently responsible for 55 percent of the costs associated with the ongoing global Phase 3 development program. Because we are leading the Phase 3 development program, we made an accounting policy election to recognize as non-customer revenue the cost-share funding from AstraZeneca, net of our share of AstraZeneca’s development expenses, in the same period we incur the related development expenses. As AstraZeneca is responsible for the majority of the commercial and medical affairs costs in the U.S. and all costs associated with bringing WAINUA to market outside the U.S., we made an accounting policy election to recognize cost-share funding we receive from AstraZeneca related to commercial and medical affairs activities as reductions of our SG&A expense and R&D expense, respectively.

4. Collaborative Arrangements and Licensing Agreements

Strategic Partnership

Biogen

We have several strategic collaborations with Biogen focused on using antisense technology to advance the treatment of neurological disorders. We developed and licensed to Biogen SPINRAZA, our approved medicine to treat people with spinal muscular atrophy, or SMA. Under our 2013 strategic neurology collaboration, Biogen developed QALSODY (tofersen), our medicine that received accelerated approval in the U.S. to treat patients with superoxide dismutase 1 amyotrophic lateral sclerosis, or SOD1-ALS. In addition, we and Biogen are currently developing numerous other investigational medicines to treat neurodegenerative diseases, including medicines in development to treat people with amyotrophic lateral sclerosis, or ALS, SMA, Angelman Syndrome, or AS, Alzheimer’s disease, or AD, and Parkinson’s disease, or PD. In addition to these medicines, our collaborations with Biogen include a substantial research pipeline that addresses a broad range of neurological diseases. From inception through December 31, 2023, we have received nearly $3.8 billion from our Biogen collaborations, including payments to purchase our stock.

Spinal Muscular Atrophy Collaborations

In 2012, we entered into a collaboration agreement with Biogen to develop and commercialize SPINRAZA. From inception through December 31, 2023, we earned more than $2.1 billion in total revenue under our SPINRAZA collaboration, including more than $1.6 billion in revenue from SPINRAZA royalties and more than $425 million in R&D revenue. We are receiving tiered royalties ranging from 11 percent to 15 percent on net sales of SPINRAZA. We have exclusively in-licensed patents related to SPINRAZA from Cold Spring Harbor Laboratory and the University of Massachusetts. We pay Cold Spring Harbor Laboratory and the University of Massachusetts a low single digit royalty on net sales of SPINRAZA. Biogen is responsible for all global development, regulatory and commercialization activities and costs for SPINRAZA. We completed our performance obligations under our collaboration in 2016.

In 2023, we entered into a royalty purchase agreement with Royalty Pharma in which Royalty Pharma receives 25 percent of our SPINRAZA royalty payments from 2023 through 2027, increasing to 45 percent of royalty payments in 2028, on up to $1.5 billion in annual sales. Royalty Pharma’s royalty interest in SPINRAZA will revert to us after total SPINRAZA royalty payments to Royalty Pharma reach either $475 million or $550 million, depending on the timing and occurrence of the U.S. Food and Drug Administration, or FDA, approval of pelacarsen, which Novartis is developing. Refer to Note 7, Long-Term Obligations and Commitments, for further discussion of this agreement.

New Antisense Medicines for the Treatment of SMA

In 2017, we entered into a collaboration agreement with Biogen toidentifynew antisense medicines for the treatment of SMA. Biogen has the option to license therapies arising out of this collaboration following the completion of preclinical studies. Upon licensing, Biogen will be responsible for global development, regulatory and commercialization activities and costs for such therapies.

At the commencement of this collaboration, we received a$25 million upfront payment from Biogen. In 2021, Biogen exercised its option to license ION 306, a drug we discovered under this collaboration, for whichwe earned a $60 million license fee payment. We recognized this payment as revenue in full because Biogen had full use of the license without any continuing involvement from us. Biogen is solely responsible for the costs and expenses related to the development, manufacturing and potential future commercialization of ION306 following the option exercise. We do not have any remaining performance obligations under this collaboration. We will receive development and regulatory milestone payments from Biogen if new medicines, including ION 306, advance towards marketing approval.

Over the term of the collaboration, we are eligible to receive up to $555 million if Biogen advances ION306, which is comprised of up to $45 million in development milestone payments, up to $110 million in regulatory milestone payments and up to $400 million in sales milestone payments. In addition, we are eligible to receive tiered royalties from the mid-teens tomid-20 percent rangeon net sales from any product that Biogen successfully commercializes under this collaboration. From inception through December 31, 2023, we received $85 million in payments under this collaboration. We will achieve the next payment of up to $45 millionfor the initiation of a Phase 3 trial under this collaboration.

Neurology Collaborations

2018 Strategic Neurology

In 2018, we and Biogen entered into a strategic collaboration to develop novel antisense medicines for a broad range of neurological diseases. We also entered into a Stock Purchase Agreement, or SPA. As part of the collaboration, Biogen gained exclusive rights to the use of our antisense technology to develop therapies for these diseases for 10 years. We are responsible for the identification of antisense drug candidates based on selected targets. In most cases, Biogen will be responsible for conducting IND-enabling toxicology studies for the selected medicine. Biogen has the option to license the selected medicine after it completes the IND-enabling toxicology study. If Biogen exercises its option to license a medicine, it will assume global development, regulatory and commercialization responsibilities and costs for that medicine.

At the commencement of this collaboration, we received$1 billion from Biogen, comprised of $625 million to purchase our stock at an approximately 25 percent cash premium and $375 million in an upfront payment.

For each medicine under this collaboration, we are eligible to receive up to $270 million, which is comprised of a $15 million license fee, up to $105 million in development milestone payments and up to $150 million in regulatory milestone payments. In addition, we are eligible to receive tiered royaltiesup to the 20 percent rangeon net sales from any product that Biogen successfully commercializes under this collaboration. We are currently advancing multiple programs under this collaboration. From inception through December 31, 2023, we have received nearly $1.1 billion in payments under this collaboration, including payments to purchase our stock. We will achieve the next payment of up to $15 million if Biogen licenses a medicine under this collaboration.

We considered that the collaboration agreement and SPA were negotiated concurrently and in contemplation of one another. Based on these facts and circumstances, we concluded that we should evaluate the provisions of the agreements on a combined basis. We identifiedone performance obligation, which was to perform R&D services for Biogen. We determined our transaction price to be $552 million, comprised of $375 million from the upfront payment and $177 million for the premium paid by Biogen for its purchase of our common stock. We determined the fair value of the premium we received by using the stated premium in the SPA and applying a lack of marketability discount. We included a lack of marketability discount in our valuation of the premium because Biogen received restricted shares of our common stock. We allocated the transaction price to our single performance obligation.

From inception through December 31, 2023, we have included $623 millionin upfront and milestone payments in the transaction price for our R&D services performance obligation under this collaboration, including a $7.5 million milestone payment we achieved in the fourth quarter of 2023. This milestone payment did not create a new performance obligation because it is part of our original R&D services performance obligation. Therefore, we included this amount in our transaction price for our R&D services performance obligation in the period we achieved the milestone payment. We are recognizing revenue for our R&D services performance obligation as we perform services based on our effort to satisfy our performance obligation relative to our total effort expected to satisfy our performance obligation. We currently estimate we will satisfy our performance obligation at the end of the contractual term in June 2028.

2013 Strategic Neurology

In 2013, we and Biogen entered into a strategic relationship focused on applying antisense technology to advance the treatment of neurodegenerative diseases. As part of the collaboration, Biogen gained exclusive rights to the use of our antisense technology to develop therapies for neurological diseases and has the option to license medicines resulting from this collaboration. In most cases, we are responsible for drug discovery and early development of antisense medicines and Biogen has the option to license antisense medicines after Phase 2 proof-of-concept. In 2016, we expanded our collaboration to include additional research activities we will perform. If Biogen exercises its option to license a medicine, it will assume global development, regulatory and commercialization responsibilities and costs for that medicine.

We are currently advancing four investigational medicines in development under this collaboration, includinga medicine for Parkinson’s disease (ION859), two medicines for ALS (QALSODY and ION541) anda medicine for multiple system atrophy (ION464). In 2018, Biogen exercised its option to license QALSODY, our medicine that received accelerated approval in April 2023 from the FDA for the treatment of adult patients with SOD1-ALS. As a result, Biogen is responsible for global development, regulatory and commercialization activities and costs for QALSODY.

Under the terms of the agreement, we received an upfront payment of $100 million and are eligible to receive milestone payments, license fees and royalty payments for all medicines developed under this collaboration, with the specific amounts dependent upon the modality of the molecule advanced by Biogen.

Over the term of the collaboration for QALSODY, we are eligible to receive nearly $110 million, which is comprised of a $35 million license fee we received when Biogen licensed QALSODY from us in 2018, $18 million in development milestone payments and up to $55 million in regulatory milestone payments. In addition, we are eligible to receive tiered royalties ranging from 11 percent to 15 percent on net sales of QALSODY. We will achieve the next milestone payment for QALSODY of $20 million if the European Medicines Agency, or EMA, approves Biogen’s Marketing Authorization Application, or MAA, filing of QALSODY.

For each of the other antisense molecules that are chosen for drug discovery and development under this collaboration, we are eligible to receive up to approximately $260 million, which is comprised of a $70 million license fee, up to $60 million in development milestone payments and up to $130 million in regulatory milestone payments. In addition, we are eligible to receive tiered royalties up to the mid-teens on net sales from any product that Biogen successfully commercializes under this collaboration. From inception through December 31, 2023, we have received more than $325 million in payments under our 2013 strategic neurology collaboration. We will achieve the next payment of $70 million if Biogen licenses a medicine under this collaboration.

At the commencement of our 2013 strategic neurology collaboration, we identifiedone performance obligation, which was to perform R&D services for Biogen. At inception, we determined the transaction price to be the $100 million upfront payment we received and allocated it to our single performance obligation. As we achieve milestone payments for our R&D services, we include these amounts in our transaction price for our R&D services performance obligation. We recognized revenue for our R&D services performance obligation based on our effort to satisfy our performance obligation relative to our total effort expected to satisfy our performance obligation. During 2020, we completed our remaining R&D services and recognized the remaining revenue related to this performance obligation. From inception through the completion of our R&D services performance obligation in 2020, we included $145 million in total payments in the transaction price for our R&D services performance obligation.

Under this collaboration, we have also generated additional payments that we concluded were not part of our R&D services performance obligation. We recognized each of these payments in full in the respective period we generated the payment because we did not have any performance obligations for the respective payment. For example, in 2023, we earned a$16 million milestone payment from Biogen when the FDA approved Biogen’s New Drug Application, or NDA, for QALSODY, which we recognized in full because we did not have any remaining performance obligations related to this milestone payment.

2012 Neurology

In 2012, we and Biogen entered into a collaboration agreement to develop and commercialize novel antisense medicines to treat neurodegenerative diseases. We are responsible for the development of each of the medicines through the completion of the initial Phase 2 clinical study for such medicine. Biogen has the option to license a medicine from each of the programs through the completion of the first Phase 2 study for each program. Under this collaboration, Biogen is conducting the IONIS-MAPTRx study for AD and we are currently advancing ION582 for AS. If Biogen exercises its option to license a medicine, it will assume global development, regulatory and commercialization responsibilities and costs for that medicine. In 2019, Biogen exercised its option to license IONIS-MAPTRx and as a result Biogen is responsible for global development, regulatory and commercialization activities and costs for IONIS-MAPTRx.

Under the terms of the agreement, we received an upfront payment of $30 million. For each program under this collaboration, we are eligible to receive up to $210 million, which is comprised of a license fee of up to $70 million, up to $10 million in development milestone payments and up to $130 million in regulatory milestone payments, plus a mark-up on the cost estimate of the Phase 1 and 2 studies. In addition, we are eligible to receive tiered royalties up to the mid-teens on net sales of any medicines resulting from each of thetwo programs. From inception through December 31, 2023, we have received more than $230 million in payments under this collaboration, including $39 million in milestone payments we received from Biogen for advancing ION582 during 2023 and a $10 million milestone payment we received from Biogen when Biogen advanced IONIS-MAPTRx during 2022. We will achieve the next payment of $70 million if Biogen licenses ION582 under this collaboration.

When we commenced development for IONIS-MAPTRx and ION582, we identifiedtwo separate performance obligations as our development work for each medicine. We recognized revenue as we performed services based on our effort to satisfy our performance obligation relative to the total effort expected to satisfy our performance obligations. In 2022, we completed our R&D services performance obligation for IONIS-MAPTRx. From inception through December 31, 2023, we have included $57 million in the transaction price for our IONIS-MAPTRx development performance obligation, including $19.5 million of milestone payments we earned from Biogen in 2020 when we advanced IONIS-MAPTRx. From inception through December 31, 2023, we have included $68 million in milestone payments in the transaction price for our ION582 development performance obligation, including $39 million in milestone payments we received from Biogen for advancing ION582 during 2023.

During the years ended December 31, 2023, 2022 and 2021, we earned the following revenue from our relationship with Biogen (in thousands, except percentage amounts):

Ourconsolidated balance sheets at December 31,2023 and 2022 included deferred revenue of $307.4 million and $351.2 million, respectively, related to our relationship with Biogen.

Joint Development and Commercialization Arrangement

WAINUA (Eplontersen) Collaboration

In 2021, we entered into a joint development and commercialization agreement with AstraZeneca to develop and commercialize eplontersen for the treatment of ATTR. In December 2023, the FDA approved eplontersen with the brand name, WAINUA, in the U.S. for ATTRv-PN. We are jointly developing and commercializing WAINUA with AstraZeneca in the U.S. We initially granted AstraZeneca exclusive rights to commercialize WAINUA outside the U.S., except for certain Latin American countries. In July 2023, we expanded those rights to include Latin America.

Over the term of the collaboration, we are eligible to receive up to $3.6 billion, which is comprised of a $200 million upfront payment, a $20 million license fee, up to $485 million in development and approval milestone payments and up to $2.9 billion in sales milestone payments. The agreement includes territory-specific development, commercial and medical affairs cost-sharing provisions. In addition, we are eligible to receive up to mid-20 percent royalties for sales in the U.S. and tiered royalties ranging from mid to high teens for sales outside the U.S. From inception through December 31, 2023, we have received nearly $360 million in payments under this collaboration. We will achieve the next payment of $30 million upon regulatory approval of WAINUA for ATTRv-PN in the EU under this collaboration.

We evaluated our WAINUA collaboration under ASC 808 and identified four material components: (i) the license we granted to AstraZeneca in 2021, (ii) the co-development activities that we and AstraZeneca will perform, (iii) the co-commercialization activities that we and AstraZeneca will perform and (iv) the co-medical affairs activities that we and AstraZeneca will perform.

We determined that we had a vendor-customer relationship within the scope of ASC 606 for the license we granted to AstraZeneca and as a result we hadone performance obligation. For our sole performance obligation, we determined the transaction price was the $200 million upfront payment we received in 2021. In 2023, we earned a $20 million license fee payment when we licensed rights to Latin America for WAINUA to AstraZeneca. We recognized these payments in full because we did not have any remaining performance obligations after we delivered the licenses to AstraZeneca.

We also concluded that the co-development activities, the co-commercialization activities and the co-medical affairs activities are within the scope of ASC 808 because we and AstraZeneca are active participants exposed to the risks and benefits of the activities under the collaboration. AstraZeneca is currently responsible for 55 percent of the costs associated with the ongoing global Phase 3 development program. Because we are leading the Phase 3 development program, we recognize as revenue the 55 percent of cost-share funding AstraZeneca is responsible for in the same period we incur the related development expenses. As AstraZeneca is responsible for the majority of the commercial and medical affairs costs in the U.S. and all costs associated with bringing WAINUA to market outside the U.S., we recognize cost-share funding we receive from AstraZeneca related to these activities as a reduction of our commercial and medical affairs expenses. In 2023, we earned a $50 million milestone payment when the FDA approved WAINUA for ATTRv-PN in the U.S. We recognized this milestone payment in full as joint development revenue because we did not have any remaining performance obligations related to the milestone payment.

Research and Development Partners

In addition to our collaboration for WAINUA, we have a collaboration with AstraZeneca focused on discovering and developing treatments for cardiovascular, renal and metabolic diseases, which we formed in 2015. Under our collaboration, AstraZeneca has licensed multiple medicines from us. AstraZeneca is responsible for global development, regulatory and commercialization activities and costs for each of the medicines it has licensed from us.

Over the term of the collaboration, we are eligible to receive up to $3.4 billion, which is comprised of a $65 million upfront payment, up to $290 million in license fees, up to $865 million in development milestone payments and up to $2.2 billion in regulatory milestone payments. In addition, we are eligible to receive tiered royalties up to the low teens on net sales from any product that AstraZeneca successfully commercializes under this collaboration agreement. From inception through December 31, 2023, we have received more than $300 million in payments under this collaboration. We will achieve the next payment of $10 million if AstraZeneca advances a medicine under this collaboration.

At the commencement of this collaboration, we identifiedone performance obligation, which was to perform R&D services for AstraZeneca. We determined the transaction price to be the $65 million upfront payment we received and we allocated it to our single performance obligation. We recognized revenue for our R&D services performance obligation as we performed services based on our effort to satisfy this performance obligation relative to our total effort expected to satisfy our performance obligation. We completed our performance obligation in 2021. As we achieved milestone payments for our R&D services, we included these amounts in our transaction price for our R&D services performance obligation. From inception through the completion of our performance obligation, we have included $90 million in payments in the transaction price for our R&D services performance obligation.

Under this collaboration, we have also generated additional payments that we concluded were not part of our R&D services performance obligation. We recognized each of these payments in full in the respective period we generated the payment because the payments were distinct and we did not have any performance obligations for the respective payment. For example, in 2023, we earned a $36 million payment when AstraZeneca licensed ION826 from us. We recognized this payment in full in 2023 because we did not have any remaining performance obligations after we delivered the license to AstraZeneca.

During the years ended December 31, 2023, 2022 and 2021, we earned the following revenue from our relationship with AstraZeneca (in thousands, except percentage amounts):

We didnot have any deferred revenue from our relationship with AstraZeneca at December 31, 2023 and 2022.

GSK

In 2010, we entered into a collaboration with GSK using our antisense drug discovery platform to discover and develop new medicines against targets for serious and rare diseases, including infectious diseases. Upon initiating the collaboration, we received an upfront payment of $35 million. Under our collaboration, GSK is developing bepirovirsen for the treatment of chronic hepatitis B virus infection, or HBV, infection. In 2019, following positive Phase 2 results, GSK licensed our HBV program. GSK is responsible for all global development, regulatory and commercialization activities and costs for the HBV program.

Over the term of the collaboration, we are eligible to receive nearly $260 million, which is comprised of a $25 million license fee, up to $42.5 million in development milestone payments, up to $120 million in regulatory milestone payments and up to $70 million in sales milestone payments if GSK successfully develops and commercializes bepirovirsen. In addition, we are eligible to receive tiered royalties up to the low-teens on net sales of bepirovirsen. From inception through December 31, 2023, we have received more than $105 million in an upfront payment and payments related to the HBV program.

We completed our R&D services performance obligations in 2015, therefore we do not have any remaining performance obligations under our collaboration with GSK. However, we can still earn additional payments and royalties as GSK advances the HBV program. In 2023, we earned a $ million milestone payment when GSK initiated a Phase 3 program of bepirovirsen. We recognized this milestone payment as R&D revenue in full in 2023 because we did not have any remaining performance obligations related to the milestone payment. We will achieve the next payment of $15 million if the FDA accepts an NDA filing of bepirovirsen for review.

During the years ended December 31, 2023, 2022 and 2021, we earned the following revenue from our relationship with GSK (in thousands, except percentage amounts):

We didnot have any deferred revenue from our relationship with GSK at December 31, 2023 and 2022.

Novartis

Pelacarsen Collaboration

In 2017, we initiated a collaboration with Novartis to develop and commercialize pelacarsen. Novartis is responsible for conducting and funding development and regulatory activities for pelacarsen, including a global Phase 3 cardiovascular outcomes study that Novartis initiated in 2019.

Over the term of the collaboration, we are eligible to receive up to $900 million, which is comprised of a $75 million upfront payment, a $150 million license fee, a $25 million development milestone payment, up to $290 million in regulatory milestone payments and up to $360 million in sales milestone payments. We are also eligible to receive tiered royalties in the mid-teens to low 20 percent range on net sales of pelacarsen. From inception through December 31, 2023, we have received more than $275 million in payments under this collaboration. We will achieve the next payment of $50 million if the FDA accepts an NDA filing for pelacarsen.

In conjunction with this collaboration, we entered into a SPA with Novartis. As part of the SPA, Novartis purchased 1.6 million shares of our common stock for $100 million in 2017.

At the commencement of this collaboration, we identified four separate performance obligations:

We determined that the R&D services for each medicine and the API for each medicine were distinct performance obligations.

We determined our transaction price to be $108.4 million, comprised of the following:

We allocated the transaction price based on the estimated stand-alone selling price of each performance obligation as follows:

We completed our R&D services performance obligations for olezarsen and pelacarsen in 2019. As such, we recognized all revenue we allocated to the olezarsen and pelacarsen R&D services as of the end of 2019.

We recognized revenue related to the R&D services for pelacarsen and olezarsen performance obligations as we performed services based on our effort to satisfy our performance obligations relative to our total effort expected to satisfy our performance obligations.

As described in the Biogen SPINRAZA section above, in January 2023, we entered into a royalty purchase agreement with Royalty Pharma. Under the agreement, in addition to a minority interest in SPINRAZA royalties, Royalty Pharma will receive 25 percent of any future royalty payments on pelacarsen. Refer to Note 7, Long-Term Obligations and Commitments, for further discussion of this agreement.

New Medicine for the Treatment of Lp(a)-Driven Cardiovascular Disease

In August 2023, we entered into a collaboration and license agreement with Novartis for the discovery, development and commercialization of a novel medicine for patients with Lp(a)-driven cardiovascular disease, or CVD. Novartis is solely responsible for the development, manufacturing and potential commercialization of the next generation Lp(a) therapy.

Over the term of the collaboration, we are eligible to receive up to $730 million, which is comprised of a $60 million upfront payment, up to $155 million in development milestone payments, up to $105 million in regulatory milestone payments and up to $410 million in sales milestone payments. In addition, we are eligible to receive tiered royalties ranging from 10 percent to 20 percent on net sales. From inception through December 31, 2023, we have received $60 million from the upfront payment we received under this collaboration. We will achieve the next payment of $5 million if we designate a development candidate under this collaboration.

At the commencement of this collaboration, we identifiedone performance obligation, which was to perform R&D services for Novartis. We determined the transaction price to be the $60 million upfront payment we received in the fourth quarter 2023. We allocated the transaction price to our single performance obligation. We are recognizing revenue for our R&D services performance obligation as we perform services based on our effort to satisfy our performance obligation relative to our total effort expected to satisfy our performance obligation. We currently estimate we will satisfy our performance obligation at the end of the research term in June 2024.

During the years ended December 31, 2023, 2022 and 2021, we earned the following revenue from our relationship with Novartis (in thousands, except percentage amounts):

Our consolidated balance sheet at December 31, 2023 included deferred revenue of $30.0 million related to our relationship with Novartis. We didnot have any deferred revenue from our relationship with Novartis at December 31, 2022.

Roche

Huntington’s Disease

In 2013, we entered into an agreement with Hoffmann-La Roche Inc and F. Hoffmann-La Roche Ltd, collectively Roche, to develop treatments for HD based on our antisense technology. Under the agreement, we discovered and developed tominersen, an investigational medicine targeting HTT protein. We developed tominersen through completion of our Phase 1/2 clinical study in people with early-stage HD. In 2017, upon completion of the Phase 1/2 study, Roche exercised its option to license tominersen. As a result, Roche is responsible for all global development, regulatory and commercialization activities and costs for tominersen.

Over the term of the collaboration, we are eligible to receive up to $395 million, which is comprised of a $30 million upfront payment, a $45 million license fee, up to $70 million in development milestone payments, up to $170 million in regulatory milestone payments and up to $80 million in sales milestone payments as tominersen advances. In addition, we are eligible to receive up to $136.5 million in milestone payments for each additional medicine successfully developed. We are also eligible to receive tiered royalties up to the mid-teens on net sales of any product resulting from this collaboration. From inception through December 31, 2023, we have received more than $150 million in payments under this collaboration. We will achieve the next payment of $17.5 million if Roche advances a medicine under this collaboration.

At the commencement of this collaboration, we identifiedone performance obligation, which was to perform R&D services for Roche. We determined the transaction price to be the $30 million upfront payment we received and allocated it to our single performance obligation. As we achieved milestone payments for our R&D services, we included these amounts in our transaction price for our R&D services performance obligation. We recognized revenue for our R&D services performance obligation over our period of performance, which ended in 2017.

Under this collaboration, we have also generated additional payments that we concluded were not part of our R&D services performance obligation. We recognized each of these payments in full in the respective period in which we generated the payment because the payments were distinct and we did not have any performance obligations for the respective payment. In 2021, Roche decided to discontinue dosing in the Phase 3 GENERATION HD1 study of tominersen in patients with manifest HD based on the results of a pre-planned review of data from the Phase 3 study conducted by an unblinded independent data monitoring committee, or iDMC.

In January 2023, Roche initiated the Phase 2, GENERATION HD2, study of tominersen in patients with prodromal or early manifest HD. Roche is focusing on early-stage and younger patients based on the post-hoc analyses from the GENERATION HD1 study that suggested tominersen may benefit these patient groups. We do not have any remaining performance obligations related to tominersen under this collaboration with Roche; however, we can still earn additional payments and royalties as Roche advances tominersen.

IONIS-FB-LRx for Complement-Mediated Diseases

In 2018, we entered into a collaboration agreement with Roche to develop IONIS-FB-LRx for the treatment of complement-mediated diseases. We are currently conducting multiple studies intwo disease indications for IONIS-FB-LRx, one for the treatment of patients with immunoglobulin A, or IgA, nephropathy, or IgAN, andone for the treatment of patients with GA, the advanced stage of dry AMD. In April 2023, Roche initiated a Phase 3 study of IONIS-FB-LRx in patients with IgAN.

After positive data from a Phase 2 clinical study in patients with IgAN, Roche licensed IONIS-FB-LRx in 2022 for $35 million. As a result, Roche is responsible for global development, regulatory and commercialization activities, and costs for IONIS-FB-LRx, except for the open label Phase 2 study in patients with IgAN and the Phase 2 study in patients with GA, both of which we are conducting and funding. In 2022, we amended our IONIS-FB-LRx collaboration agreement with Roche. The amendment changed future potential milestone payments we could receive under the collaboration. We determined there were no changes that would require adjustments to revenue we previously recognized.

Over the term of the collaboration, we are eligible to receive more than $810 million, which is comprised of a $75 million upfront payment, a $35 million license fee, up to $145 million in development milestone payments, up to $279 million in regulatory milestone payments and up to $280 million in sales milestone payments. In addition, we are also eligible to receive tiered royalties from the high teens to 20 percent on net sales. From inception through December 31, 2023, we have received more than $135 million in payments under this collaboration. We will achieve the next payment of up to $90 million if Roche advances IONIS-FB-LRx under this collaboration.

At the commencement of this collaboration, we identifiedone performance obligation, which was to perform R&D services for Roche. From inception through December 31, 2023, we have included $97 million in upfront and milestone payments in the transaction price for our R&D services performance obligation under this collaboration, including $22 million of milestone payments we achieved in 2022. We are recognizing revenue for our R&D services performance obligation as we perform services based on our effort to satisfy our performance obligation relative to our total effort expected to satisfy our performance obligation. We currently estimate we will satisfy our performance obligation inthe fourth quarter of 2024.

RNA-Targeting Medicines for Alzheimer's Disease and Huntington's Disease

In September 2023, we entered into an agreement with Roche to developtwo undisclosed early-stage programs for RNA-targeting investigational medicines for the treatment of AD and HD. Under the agreement, we are responsible for advancing thetwo programs through preclinical studies and Roche is responsible for clinical development, manufacturing and commercialization of the medicines if they receive regulatory approval.

Over the term of the collaboration, we are eligible to receive up to $625 million, which is comprised of a $60 million upfront payment, up to $167 million in development milestone payments and up to $398 million in sales milestone payments. In addition, we are eligible to receive tiered royalties up to the mid-teens on net sales. From inception through December 31, 2023, we have received $60 million from the upfront payment we received under this collaboration. We will achieve the next payment of $7.5 million if we advance a medicine under this collaboration.

We identifiedtwo performance obligations under this new agreement, comprised of R&D services for each of thetwo separate programs. We determined the transaction price to be the $60 million upfront payment we received in the fourth quarter 2023. We allocated the transaction price based on the estimated stand-alone selling price of each performance obligation as follows:

We are recognizing revenue for our R&D services performance obligations as we perform services based on our effort to satisfy our performance obligations relative to our total effort expected to satisfy our performance obligations. We currently estimate we will satisfy our performance obligations at the end of the research terms of March 2024 and March 2025 for the investigational medicines for AD and HD, respectively.

During the years ended December 31, 2023, 2022 and 2021, we earned the following revenue from our relationship with Roche (in thousands, except percentage amounts):

Ourconsolidated balance sheets at December 31,2023 and 2022 included deferred revenue of $36.7 million and $22.4 million related to our relationship with Roche, respectively.

Commercialization Partnerships

Otsuka

In December 2023, we entered into an agreement with Otsuka Pharmaceutical Co., Ltd., or Otsuka, to commercialize donidalorsen in Europe. We are responsible for the ongoing development of donidalorsen. We retained the rights to commercialize donidalorsen in the U.S. and in the rest of the world assuming regulatory approval.

Over the term of the collaboration, we are eligible to receive up to $185 million, which is comprised of a $65 million upfront payment, up to $50 million in regulatory milestone payments and up to $70 million in sales milestone payments. In addition, we are eligible to receive tiered royalties ranging from 20 percent to 30 percent on net sales. From inception through December 31, 2023, we have received $65 million from the upfront payment we received under this collaboration. We will achieve the next payment of $15 million if the EMA accepts a MAA filing for donidalorsen in the EU under this collaboration.

We identifiedtwo performance obligations under this new agreement, comprised of our license of donidalorsen to Otsuka and R&D services for donidalorsen. We determined the transaction price to be the $65 million upfront payment we received in the fourth quarter 2023. We allocated the transaction price based on the estimated stand-alone selling price of each performance obligation as follows:

We are recognizing revenue for our R&D services performance obligation as we perform services based on our effort to satisfy our performance obligation relative to our total effort expected to satisfy our performance obligation. We currently estimate we will satisfy our performance obligations in March 2026.

During the year ended December 31, 2023, we earned the following revenue from our relationship with Otsuka (in thousands, except percentage amount):

Ourconsolidated balance sheets at December 31,2023 included deferred revenue of $8.5 million related to our relationship with Otsuka.

PTC Therapeutics

In 2018, we entered into an exclusive license agreement with PTC Therapeutics to commercialize TEGSEDI and WAYLIVRA in Latin America and certain Caribbean countries. Under the license agreement, we are eligible to receive royalties from PTC in the mid-20 percent range on net sales for each medicine. In December 2021 and September 2023, we started receiving royalties from PTC for TEGSEDI and WAYLIVRA sales, respectively.

Swedish Orphan Biovitrum AB (Sobi)

In 2021, we began commercializing TEGSEDI and WAYLIVRA in Europe and TEGSEDI in North America through distribution agreements with Sobi. Under our distribution agreements, Sobi is responsible for commercializing TEGSEDI and WAYLIVRA in Europe and TEGSEDI in North America, respectively. We are responsible for supplying finished goods inventory to Sobi and Sobi is responsible for selling each medicine to the end customer. Under our agreements with Sobi, Sobi does not generally have a right of return. We recognize as revenue the price Sobi pays us for the inventory when we deliver the finished goods inventory to Sobi. In addition, we earn a distribution fee on net sales from Sobi for each medicine.

In October 2023, our distribution agreement for TEGSEDI in North America was terminated. As a result, we are currently transitioning responsibilities from Sobi to us in order to continue serving the impacted patient community. In February 2024, we began the process to withdraw the TEGSEDI NDA.

During the years ended December 31, 2023, 2022 and 2021, we earned the following revenue from our distribution agreement with Sobi for TEGSEDI in North America (in thousands, except percentage amounts):

Technology Enhancement Collaborations

Bicycle Therapeutics

In 2020, we entered into a collaboration agreement with Bicycle and obtained an option to license its peptide technology to potentially increase the delivery capabilities of our LICA medicines. In 2021, we paid $42 million when we exercised our option to license Bicycle’s technology, which included an equity investment in Bicycle. As part of our stock purchase, we entered into a lockup agreement with Bicycle that restricted our ability to trade our Bicycle shares forone year. In 2021, we recorded a $7.2 million equity investment for the shares we received in Bicycle. We recognized the remaining $34.8 million as R&D expense in 2021.

Metagenomi

In 2022, we entered into a collaboration and license agreement with Metagenomi to research, develop and commercialize investigational medicines for up tofour initial genetic targets, and, upon the achievement of certain development milestones, four additional genetic targets using gene editing technologies. As a result, we paid $80 million to license Metagenomi’s technologies and will pay Metagenomi certain fees for the selection of genetic targets. We recorded the $80 million payment as R&D expense in 2022 upon receiving a license from Metagenomi for intellectual property that is in research with no current alternate use. In addition, we will pay Metagenomi milestone payments and royalties that are contingent on the achievement of certain development, regulatory and sales events. We will also reimburse Metagenomi for certain of its costs in conducting its research and drug discovery activities under the collaboration.

Other Agreements

Alnylam Pharmaceuticals, Inc.

Under the terms of our agreement with Alnylam, we co-exclusively (with ourselves) licensed to Alnylam our patent estate relating to antisense motifs and mechanisms and oligonucleotide chemistry for double-stranded RNAi therapeutics, with Alnylam having the exclusive right to grant platform sublicenses for double-stranded RNAi. In exchange for such rights, Alnylam gave us a technology access fee, participation in fees from Alnylam’s partnering programs, as well as future milestone and royalty payments from Alnylam. We retained exclusive rights to our patents for single-stranded antisense therapeutics and for a limited number of double-stranded RNAi therapeutic targets and all rights to single-stranded RNAi, or ssRNAi, therapeutics. In turn, Alnylam nonexclusively licensed to us its patent estate relating to antisense motifs and mechanisms and oligonucleotide chemistry to research, develop and commercialize single-stranded antisense therapeutics, ssRNAi therapeutics, and to research double-stranded RNAi compounds. We also received a license to develop and commercialize double-stranded RNAi therapeutics targeting a limited number of therapeutic targets on a nonexclusive basis. Additionally, in 2015, we and Alnylam entered into an alliance in which we cross-licensed intellectual property. Under this alliance, we and Alnylam each obtained exclusive license rights tofour therapeutic programs. Alnylam granted us an exclusive, royalty-bearing license to its chemistry, RNA targeting mechanism and target-specific intellectual property for oligonucleotides against four targets, including FXI and Apo(a) andtwo other targets. In exchange, we granted Alnylam an exclusive, royalty-bearing license to our chemistry, RNA targeting mechanism and target-specific intellectual property for oligonucleotides against four other targets. Alnylam also granted us a royalty-bearing, non-exclusive license to new platform technology arising from May 2014 through April 2019 for single-stranded antisense therapeutics. In turn, we granted Alnylam a royalty-bearing, non-exclusive license to new platform technology arising from May 2014 through April 2019 for double-stranded RNAi therapeutics.

During the years ended December 31, 2023, 2022 and 2021, we earned the following revenue from our relationship with Alnylam (in thousands, except percentage amounts):

We didnot have any deferred revenue from our relationship with Alnylam at December 31, 2023 and 2022.

5. Investments

The following table summarizes the contract maturity of the available-for-sale securities we held as of December 31, 2023:

As illustrated above, at December 31, 2023,92 percent of our available-for-sale securities had a maturity of less thantwo years.

All of our available-for-sale securities are available to us for use in our current operations. As a result, we categorize all of these securities as current assets even though the stated maturity of some individual securities may be one year or more beyond the balance sheet date.

We invest in debt securities with strong credit ratings and an investment grade rating at or above A-1, P-1 or F-1 by Standard & Poor’s, Moody’s or Fitch, respectively.

At December 31, 2023, we had an ownership interest of less than 20 percentin seven private companies andthree public companies with which we conduct business.

The following is a summary of our investments (in thousands):

The following is a summary of our investments we considered to be temporarily impaired at December 31, 2023 (in thousands, except for number of investments):

We believe that the decline in value of these securities is temporary and is primarily related to the change in market interest rates since purchase rather than underlying credit deterioration for any of the issuers. We believe it is more likely than not that we will be able to hold our debt securities with declines in value to maturity. Therefore, we intend to hold these securities to maturity and anticipate full recovery of our debt securities’ amortized cost basis at maturity.

6. Fair Value Measurements

The following tables present the major security types we held at December 31, 2023 and 2022 that we regularly measure and carry at fair value. The following tables segregate each security type by the level within the fair value hierarchy of the valuation techniques we utilized to determine the respective securities’ fair value (in thousands):

Convertible Notes

Our 1.75% Notes,0% Notes and 0.125% Notes had a fair value of $661.1 million, $667.8 million and $42.4 million at December 31, 2023, respectively. We determine the fair value of our notes based on quoted market prices for these notes, which are Level 2 measurements because the notes do not trade regularly.

7. Long-Term Obligations and Commitments

The carrying value of our long-term obligations was as follows (in thousands):

As of December 31, 2023, our 0.125% Notes was classified as a current liability because it matures in December 2024.

Convertible Debt and Call Spread

1.75% Convertible Senior Notes

In 2023, we completed a $575.0 million offering of convertible senior notes and used $488.2 million of the net proceeds from the issuance of the 1.75% Notes to repurchase $504.4 million in principal of our 0.125% Notes. We expect to use the remaining net proceeds to settle the 0.125% Notes that remain outstanding.

At December 31, 2023, we had the following 1.75% Notes outstanding (in millions, except interest rate and price per share data):

0% Convertible Senior Notes and Call Spread

In 2021, we completed a $632.5 million offering of convertible senior notes. We used $319.0 million of the net proceeds from the issuance of the 0% Notes to pay the remaining $309.9 million principal balance of our 1% Notes in 2021.

At December 31, 2023, we had the following 0% Notes outstanding (in millions, except interest rate and price per share data):

In conjunction with the 2021 offering, we entered into a call spread transaction, which was comprised of purchasing note hedges and selling warrants, to minimize the impact of potential economic dilution upon conversion of our 0% Notes by increasing the effective conversion price on our 0% Notes. We increased our effective conversion price to $76.39 with the same number of underlying shares as our 0% Notes. The call spread cost us $46.9 million, of which $136.7 million was for the note hedge purchase, offset by $89.8 million we received for selling the warrants. Similar to our 0% Notes, our note hedges are subject to adjustment. Additionally, our note hedges are exercisable upon conversion of the 0% Notes. The note hedges will expire upon maturity of the 0% Notes, or April 2026. The note hedges and warrants are separate transactions and are not part of the terms of our 0% Notes. The holders of the 0% Notes do not have any rights with respect to the note hedges and warrants.

We recorded the amount we paid for the note hedges and the amount we received for the warrants in additional paid-in capital in our consolidated balance sheets. Refer to Note 1, Organization and Significant Accounting Policies, for our Call Spread accounting policy. We reassess our ability to continue to classify the note hedges and warrants in shareholders’ equity at each reporting period.

0.125% Convertible Senior Notes and Call Spread

In 2019, we entered into privately negotiated exchange and/or subscription agreements with certain new investors and certain holders of our 1% Notes to exchange $375.6 million of our 1% Notes for $439.3 million of our 0.125% Notes, and to issue $109.5 million of our 0.125% Notes.

As discussed above, in 2023, we repurchased $504.4 million of our 0.125% Notes. We are holding the repurchased 0.125% Notes in treasury until maturity. As a result, the remaining principal balance of our 0.125% Notes was $44.5 million as of December 31, 2023. Additionally, during the year ended December 31, 2023, we recorded a $13.4 million gain on the early retirement of debt, which we recorded as other income in our consolidated statements of operations. The gain on the early retirement of our debt is the difference between the amounts paid to repurchase our 0.125% Notes and the net carrying balance of the liability at the time that we completed the repurchases.

At December 31, 2023, we had the following 0.125% Notes outstanding with interest payable semi-annually (in millions, except interest rate and price per share data):

In conjunction with the issuance of our 0.125% Notes in 2019, we entered into a call spread transaction, which was comprised of purchasing note hedges and selling warrants, to minimize the impact of potential economic dilution upon conversion of our 0.125% Notes by increasing the effective conversion price on our 0.125% Notes. We increased our effective conversion price to $123.38 with the same number of underlying shares as our 0.125% Notes. The call spread cost us $52.6 million, of which $108.7 million was for the note hedge purchase, offset by $56.1 million we received for selling the warrants. Similar to our 0.125% Notes, our note hedges are subject to adjustment. Additionally, our note hedges are exercisable upon conversion of the 0.125% Notes. The note hedges will expire upon maturity of the 0.125% Notes, or December 2024. The note hedges and warrants are separate transactions and are not part of the terms of our 0.125% Notes. The holders of the 0.125% Notes do not have any rights with respect to the note hedges and warrants.

We recorded the amount we paid for the note hedges and the amount we received for the warrants in additional paid-in capital in our consolidated balance sheets. Refer to Note 1, Organization and Significant Accounting Policies, for our Call Spread accounting policy. We reassess our ability to continue to classify the note hedges and warrants in shareholders’ equity at each reporting period.

Other Terms of Convertible Senior Notes

The 1.75%,0% and 0.125% Notes are convertible under certain conditions, at the option of the note holders. We can settle conversions of the notes, at our election, in cash, shares of our common stock or a combination of both. We may not redeem the notes prior to maturity, and we do not have to provide a sinking fund for them. Holders of the notes may require us to purchase some or all of their notes upon the occurrence of certain fundamental changes, as set forth in the indentures governing the notes, at a purchase price equal to 100 percent of the principal amount of the notes to be purchased, plus any accrued and unpaid interest.

Our total interest expense for our outstanding senior convertible notes for the years ended December 31, 2023, 2022 and 2021 included $5.9 million, $5.3 million and $4.9 million, respectively, of non-cash interest expense related to the amortization of debt issuance costs for our convertible notes.

Financing Arrangements

Operating Facilities

In 2017, we purchased the building that houses our primary R&D facility for $79.4 million and our manufacturing facility for $14.0 million. We financed the purchase of thesetwo facilities with mortgage debt of $60.4 million in total. Our primary R&D facility mortgage had an interest rate of 3.88 percent. Our manufacturing facility mortgage has an interest rate of 4.20 percent. During the first five years of both mortgages, we were only required to make interest payments. We began making principal payments in 2022. Our manufacturing facility mortgage matures in August 2027. We repaid our primary R&D facility mortgage in 2022 in conjunction with a sale and leaseback transaction.

In 2022, we concurrently entered intotwo purchase and sale agreements with a real estate investor. In the same period, we closed the first transaction in which we sold the facilities at our headquarters in Carlsbad, California, which includes our primary R&D facility, for a purchase price of $263.4 million. As a result, we de-recognized the related land and improvements, building and building improvements, which resulted in a net gain of $150.1 million that we reported in other income in our consolidated statements of operations. We used a portion of the sale proceeds to extinguish our outstanding mortgage debt on our primary R&D facility of $51.3 million. In connection with this transaction, we leased back our headquarters facilities for an initial lease term of 15 years with options to extend the lease fortwo additional terms offive years each.

In August 2023, we closed the second transaction and transferred legal ownership oftwo lots of undeveloped land adjacent to our headquarters to the real estate investor for a purchase price of $33 million. In connection with this transaction, we entered into a build-to-suit lease agreement with the same real estate investor to lease a new R&D facility. The lessor will develop and construct a new building composed of R&D and office space. We will design and construct tenant improvements to customize the facility’s interior space. We will lease the facility for an initial term of 15 years with options to extend the lease fortwo additional terms offive years each. The lease will commence once the structure of this new facility is completed.

Since the building is under construction and unavailable to lease, we are unable to complete the sale-leaseback evaluation under ASC 842, Leases. As a result, the land remains in our consolidated balance sheets and we accounted for the proceeds as a financial liability. We will reassess the transaction under the sale-leaseback accounting guidance when the facilities are available for lease commencement.

Debt Maturity Schedules

Annual convertible and mortgage debt maturities, including fixed and determinable interest, at December 31, 2023 are as follows (in thousands):

Operating Leases

Carlsbad Leases

We lease a facility adjacent to our manufacturing facility that has laboratory and office space that we use to support our manufacturing facility. We lease this space under a non-cancelable operating lease. In 2020, we exercised our option to extend our lease, extending our lease term from June 2021 to August 2026. We haveone remaining option to extend the lease for an additional five-year period.

We also lease an additional office space and warehouse space in Carlsbad. We lease these spaces under non-cancelable operating leases. In 2022, we exercised our option to extend the office space lease, extending our term from January 2023 to May 2027. We haveno remaining options to extend this lease. Our warehouse space lease in Carlsbad has an initial term ending in 2028 withno options to extend the lease.

As discussed above in the section titled, Financing Arrangements, we lease our headquarters, which includes our primary R&D facility, as part of a sale and leaseback transaction that closed in 2022. The initial lease term for our headquarters facilities is 15 years with options to extend the lease fortwo additional terms offive years each. We determined at lease inception that it was not reasonably certain that we would exercise any of the options to extend the lease. We expect our lease payments over the initial term to total approximately $280 million. In connection with the transfer of legal ownership of thetwo lots of undeveloped land to the real estate investor, we entered into a build-to-suit lease agreement with the same real estate investor who will build a new R&D facility for us on those lots. The lease will commence once the structure of this new facility is completed.

Oceanside Lease

In 2022, we entered into a build-to-suit lease agreement to lease a development chemistry and manufacturing facility to be constructed by the lessor in Oceanside, California. We capitalized costs that we incurred related to the design and development of tenant improvements as construction-in-progress in our consolidated balance sheets. In August 2023, we reached a mutual agreement with the lessor to terminate the lease agreement. As a result, we recorded a charge of $20 million, primarily associated with the impairment of construction-in-progress assets, within SG&A expense in our consolidated statements of operations.

Boston Leases

We entered into an operating lease agreement for office space located in Boston, Massachusetts which commenced in August 2018. We are leasing this space under a non-cancelable operating lease with an initial term ending after 123 months and an option to extend the lease for an additional five-year term. Under the lease agreement, we received athree-month free rent period.

In 2022, we entered into a sublease agreement for our office space located in Boston, Massachusetts. The sublease commencement date was in January 2022 when the office space was ready for our tenant’s occupancy. We are subleasing this space under a non-cancelable operating sublease with a sublease term ending 83 months following the sublease commencement date withno option to extend the sublease. Under the sublease agreement we provided aseven-month free rent period, which commenced in January 2022. We will receive lease payments over the sublease term totaling $9.6 million.

We entered into an operating lease agreement for another office space located in Boston, Massachusetts which commenced in 2021. We are leasing this space under a non-cancelable operating lease with an initial term ending 91 months following the lease commencement date and an option to extend the lease foran additional five-year term. Under the lease agreement, we received aseven-month free rent period, which commenced in November 2021. Our lease payments over the initial term total $6.8 million.

When we determined our lease term for our operating lease right-of-use assets and lease liabilities for these leases, we did not include the extension options for these leases in the original lease term because it was not reasonably certain we would exercise those extension options.

Amounts related to our operating leases were as follows (dollar amounts in millions):

During the years ended December 31, 2023, 2022, and 2021 we paid $20.1 million, $4.0 million and $3.3 million of lease payments, which were included in operating activities in our consolidated statements of cash flows.

As of December 31, 2023, the future payments for our operating lease liabilities are as follows (in thousands):

Rent expense was $23.1 million, $8.3 million and $3.4 million for the years ended December 31, 2023, 2022 and 2021, respectively.

Royalty Revenue Monetization

In January 2023, we entered into a royalty purchase agreement with Royalty Pharma Investments, or Royalty Pharma, to monetize a portion of our future SPINRAZA and pelacarsen royalties we are entitled to under our agreements with Biogen and Novartis, respectively. As a result, we received an upfront payment of $500 million and we are eligible to receive up to $625 million in additional milestone payments. Under the terms of the agreement, Royalty Pharma will receive 25 percent of our SPINRAZA royalty payments from 2023 through 2027, increasing to 45 percent of royalty payments in 2028, on up to $1.5 billion in annual sales. In addition, Royalty Pharma will receive 25 percent of any future royalty payments on pelacarsen. Royalty Pharma’s royalty interest in SPINRAZA will revert to us after total SPINRAZA royalty payments to Royalty Pharma reach either $475 million or $550 million, depending on the timing and occurrence of FDA approval of pelacarsen.

We recorded the upfront payment of $500 million as a liability related to the sale of future royalties, net of transaction costs of $10.4 million, which we are amortizing over the estimated life of the arrangement using the effective interest rate method. We recognize royalty revenue in the period in which the counterparty sells the related product and recognizes the related revenue. We record royalty payments made to Royalty Pharma as a reduction of the liability.

We determine the effective interest rate used to record interest expense under this agreement based on an estimate of future royalty payments to Royalty Pharma. As of December 31, 2023, the estimated effective interest rate under the agreement was 13.5 percent.

The following is a summary of our liability related to sale of future royalties for the year ended December 31, 2023 (in thousands):

There are numerous factors, most of which are not within our control, that could materially impact the amount and timing of royalty payments from Biogen and Novartis, and result in changes to our estimate of future royalty payments to Royalty Pharma. Such factors include, but are not limited to, the commercial sales of SPINRAZA, the regulatory approval and commercial sales of pelacarsen, competing products or other significant events.

8. Stockholders’ Equity

Preferred Stock

We are authorized to issue up to 15 million shares of “blank check” Preferred Stock. As of December 31, 2023, there wereno shares of Preferred Stock outstanding. We have designated Series C Junior Participating Preferred Stock but haveno issued or outstanding shares as of December 31, 2023.

Common Stock

At December 31, 2023 and 2022, we had 300 million shares of common stock authorized, of which 144.3 million and 142.1 million were issued and outstanding, respectively. As of December 31, 2023, total common shares reserved for future issuance were 49.7 million.

During the years ended December 31, 2023, 2022 and 2021, we issued 2.3 million,1.2 million and 1.1 million shares of common stock, respectively, for stock option exercises, vesting of restricted stock units, and ESPP purchases. We received net proceeds from these transactions of $49.4 million, $6.4 million and $11.6 million in 2023, 2022 and 2021, respectively.

Stock Plans

1989 Stock Option Plan

In 1989, our Board of Directors adopted, and the stockholders subsequently approved, a stock option plan that, as amended, provides for the issuance of non-qualified and incentive stock options for the purchase of up to 20.0 million shares of common stock to our employees, directors, and consultants. The plan expires in January 2024. The 1989 Stock Option Plan, or 1989 Plan, does not allow us to grant stock bonuses or restricted stock awards and prohibits us from repricing any options outstanding under the plan unless our stockholders approve the repricing. Options vest over afour-year period, with 25 percent exercisable at the end ofone year from the date of the grant and the balance vesting ratably, on a monthly basis, thereafter and have a term ofseven years. At December 31, 2023, no options were outstanding and 68,000 shares were available for future grant under the 1989 Plan.

2011 Equity Incentive Plan

In 2011, our Board of Directors adopted, and the stockholders subsequently approved, a stock option plan that provides for the issuance of stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, and performance cash awards to our employees, directors, and consultants. In June 2015, May 2017 and June 2019, after receiving approval from our stockholders, we amended our 2011 Equity Incentive Plan, or 2011 Plan, to increase the total number of shares reserved for issuance. We increased the shares available under our 2011 Equity Incentive Plan from 5.5 million to 11.0 million in June 2015, from 11.0 million to 16.0 million in May 2017 and from 16.0 million to 23.0 million in June 2019. In June 2021, after receiving approval from our stockholders, we amended our 2011 Plan. The amendment increased the total number of shares of common stock authorized for issuance under the 2011 Plan from 23.0 million to 29.7 million and added a fungible share counting ratio whereby the share reserve will be reduced by 1.7 shares for each share of common stock issued pursuant to a full value award (i.e., RSU or PRSU) and increased by 1.7 shares for each share of common stock returning from a full value award. In June 2023, after receiving approval from our stockholders, we amended our 2011 Plan to increase the total number of shares of common stock authorized for issuance under the 2011 Plan from 29.7 million to 35.2 million.

The plan expires in June 2031. The 2011 Plan does not allow us to reduce the exercise price of any outstanding stock options or stock appreciation rights or cancel any outstanding stock options or stock appreciation rights that have an exercise price or strike price greater than the current fair market value of the common stock in exchange for cash or other stock awards unless our stockholders approve such action. Currently we anticipate awarding only stock options, RSU and PRSU awards to our employees, directors and consultants. Options vest over afour-year period, with 25 percent exercisable at the end ofone year from the date of the grant and the balance vesting ratably, on a monthly basis, thereafter and have a term ofseven years. Options granted after December 31, 2021 have a term often years. We have granted restricted stock unit awards to our employees under the 2011 Plan which vest annually over afour-year period. At December 31, 2023, a total of 12.8 million options were outstanding, of which 8.7 million were exercisable,3.3 million restricted stock unit awards were outstanding, and 8.0 million shares were available for future grant under the 2011 Plan.

Under the 2011 Plan, we may issue a stock award with additional acceleration of vesting and exercisability upon or after a change in control. In the absence of such provisions, no such acceleration will occur. In addition, we implemented a change of control and severance benefit plan that provides for change of control and severance benefits to our executive officers, including our chief executive officer and chief financial officer, and vice presidents. Ifone of our executive officers or vice presidents is terminated or resigns for good reason during the period that begins three months before and ends twelve months following a change in control of the company, the impacted employee’s stock options and RSUs vesting will accelerate for options and RSUs outstanding as of the termination date.

2020 Equity Incentive Plan

In connection with the Akcea Merger in 2020, we assumed the unallocated portion of the available share reserve under the Akcea 2015 Equity Incentive Plan. In 2020, we amended and restated the Akcea 2015 equity plan, including renaming the plan as the Ionis Pharmaceuticals, Inc. 2020 Equity Incentive Plan, or 2020 Plan. The 2020 Plan provided for the issuance of up to 2.6 million shares of our Common Stock to our employees, directors and consultants who were employees of Akcea prior to the Akcea Merger. In the second quarter of 2021, our Compensation Committee approved an amendment to the 2020 Plan. The amendment decreased the total number of shares of common stock authorized for issuance under the 2020 Plan from approximately 2.6 million to 1.6 million. We assumed the 2020 Plan in connection with Ionis’ reacquisition of all of the outstanding shares of Akcea Therapeutics, Inc. as part of the Akcea Merger.

The plan expires in December 2025. The 2020 Plan does not allow us to reduce the exercise price of any outstanding stock options or stock appreciation rights or cancel any outstanding stock options or stock appreciation rights that have an exercise price or strike price greater than the current fair market value of the common stock in exchange for cash or other stock awards unless our stockholders approve such action. Currently we anticipate awarding only stock options and RSU awards to our eligible employees, directors and consultants. Options vest over afour-year period, with 25 percent exercisable at the end ofone year from the date of the grant and the balance vesting ratably, on a monthly basis, thereafter and have a term ofseven years. Options granted after December 31, 2021 have a term often years. We have granted restricted stock unit awards to our employees under the 2020 Plan which vest annually over afour-year period. At December 31, 2023, a total of 0.4 million options were outstanding, of which 0.1 million were exercisable,0.2 million restricted stock unit awards were outstanding, and 1.0 million shares were available for future grant under the 2020 Plan.

Under the 2020 Plan, we may issue a stock award with additional acceleration of vesting and exercisability upon or after a change in control. In the absence of such provisions, no such acceleration will occur.

Corporate Transactions and Change in Control under 2011 and 2020 Plans

In the event of certain significant corporate transactions, our Board of Directors has the discretion to take one or more of the following actions with respect to outstanding stock awards under the 2011 and 2020 Plans:

2002 Non-Employee Directors’ Stock Option Plan

In 2001, our Board of Directors adopted, and the stockholders subsequently approved, an amendment and restatement of the 1992 Non-Employee Directors’ Stock Option Plan, which provides for the issuance of non-qualified stock options and restricted stock units to our non-employee directors. The name of the resulting plan is the 2002 Non-Employee Directors’ Stock Option Plan, or the 2002 Plan. In 2015, after receiving approval from our stockholders, we amended our 2002 Plan to increase the total number of shares reserved for issuance from 1.2 million to 2.0 million. In 2020, after receiving approval from our stockholders, we further amended our 2002 Plan. The amendments included:

Options under this plan expire 10 years from the date of grant. At December 31, 2023, a total of 0.9 million options were outstanding, of which 0.9 million were exercisable,40,000 restricted stock unit awards were outstanding, and 0.5 million shares were available for future grant under the 2002 Plan.

Employee Stock Purchase Plan

In 2009, our Board of Directors adopted, and the stockholders subsequently approved, the amendment and restatement of the ESPP and we reserved an additional 150,000 shares of common stock for issuance thereunder. In each of the subsequent years until 2019, we reserved an additional 150,000 shares of common stock for the ESPP resulting in a total of 3.2 million shares authorized under the plan as of December 31, 2023. The ESPP permits full-time employees to purchase common stock through payroll deductions (which cannot exceed 10 percent of each employee’s compensation) at the lower of 85 percent of fair market value at the beginning of the purchase period or the end of each purchase period. Under the amended and restated ESPP, employees must hold the stock they purchase for a minimum ofsix months from the date of purchase. During 2023, employees purchased and we issued to employees 0.1 million shares under the ESPP at a weighted average price of $30.53 per share. At December 31, 2023, there were 0.4 million shares available for purchase under the ESPP.

Stock Option Activity

The following table summarizes the stock option activity under our stock plans for the year ended December 31, 2023 (in thousands, except per share and contractual life data):

The weighted-average estimated fair values of options granted were $19.72, $18.66 and $24.35 for the years ended December 31, 2023, 2022 and 2021, respectively. The total intrinsic value of options exercised during the years ended December 31, 2023, 2022 and 2021 were $6.0 million, $1.4 million and $2.5 million, respectively, which we determined as of the date of exercise. The amount of cash received from the exercise of stock options was $65.1 million, $3.6 million and $8.5 million for the years ended December 31, 2023, 2022 and 2021, respectively. For the year ended December 31, 2023, the weighted-average fair value of options exercised was $49.23. As of December 31, 2023, total unrecognized compensation cost related to non-vested stock options was $36.6 million. We expect to recognize this cost over a weighted average period of 1.1 years. We will adjust the total unrecognized compensation cost for future changes in estimated forfeitures.

Restricted Stock Unit Activity

The following table summarizes the RSU activity for the year ended December 31, 2023 (in thousands, except per share data):

For the years ended December 31, 2023, 2022 and 2021, the weighted-average grant date fair value of RSUs granted was $40.51, $36.14 and $57.02 per RSU, respectively. As of December 31, 2023, total unrecognized compensation cost related to RSUs was $53.7 million. We expect to recognize this cost over a weighted average period of 1.3 years. We will adjust the total unrecognized compensation cost for future changes in estimated forfeitures.

Performance Restricted Stock Unit Activity

The following table summarizes the PRSU activity for the year ended December 31, 2023 (in thousands, except per share data):

For the years ended December 31, 2023, 2022 and 2021, the weighted-average grant date fair value of PRSUs granted was $57.43, $42.28 and $77.17 per PRSU, respectively. As of December 31, 2023, total unrecognized compensation cost related to PRSUs was $4.4 million. We expect to recognize this cost over a weighted average period of 1.4 years. We will adjust the total unrecognized compensation cost for future changes in estimated forfeitures.

Stock-based Compensation Expense and Valuation Information

The following table summarizes stock-based compensation expense for the years ended December 31, 2023, 2022 and 2021 (in thousands):

Refer to Note 1, Organization and Significant Accounting Policies, for further details on how we determine the fair value of stock options granted, RSUs, PRSUs and stock purchase rights under the ESPP.

For the years ended December 31, 2023, 2022 and 2021, we used the following weighted-average assumptions in our Black-Scholes calculations:

Employee Stock Options:

Board of Director Stock Options:

ESPP:

Risk-Free Interest Rate. We base the risk-free interest rate assumption on observed interest rates appropriate for the term of our stock option plans or ESPP.

Dividend Yield. We base the dividend yield assumption on our history and expectation of dividend payouts. We have not paid dividends in the past and do not expect to in the future.

Volatility. We use an average of the historical stock price volatility of our stock for the Black-Scholes model. We computed the historical stock volatility based on the expected term of the awards.

Expected Life. The expected term of stock options we have granted represents the period of time that we expect them to be outstanding. Historically, we estimated the expected term of options we have granted based on actual and projected exercise patterns. In 2021, our Compensation Committee approved an amendment to the 2011 Equity Incentive Plan, or 2011 Plan, and the 2020 Equity Incentive Plan, or 2020 Plan, that increased the contractual term of stock options granted under these plans from seven toten years for stock options granted on January 1, 2022 and thereafter. We determined that we are unable to rely on our historical exercise data as a basis for estimating the expected life of stock options granted to employees following this change because the contractual term changed and we have no other means to reasonably estimate future exercise behavior. We therefore used the simplified method for determining the expected life of stock options granted to employees in the years ended December 31, 2023 and 2022. Under the simplified method, we calculate the expected term as the average of the time-to-vesting and the contractual life of the options. As we gain additional historical information, we will transition to calculating our expected term based on our historical exercise patterns.

Forfeitures. We reduce stock-based compensation expense for estimated forfeitures. We estimate forfeitures at the time of grant and revise, if necessary, in subsequent periods if actual forfeitures differ from those estimates. We estimate forfeitures based on historical experience.

9. Income Taxes

Loss before income taxes is comprised of (in thousands):

Our income tax expense (benefit) was as follows (in thousands):

Our expense (benefit) for income taxes differs from the amount computed by applying the U.S. federal statutory rate to loss before income taxes. The sources and tax effects of the differences are as follows (in thousands):

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes.

Significant components of our deferred tax assets and liabilities as of December 31, 2023 and 2022 are as follows (in thousands):

We evaluate our deferred tax assets regularly to determine whether adjustments to the valuation allowance are appropriate due to changes in facts or circumstances, such as changes in expected future pre-tax earnings, tax law, interactions with taxing authorities and developments in case law. In making this evaluation, we rely on our recent history of pre-tax earnings. Our material assumptions are our forecasts of future pre-tax earnings and the nature and timing of future deductions and income represented by the deferred tax assets and liabilities, all of which involve the exercise of significant judgment. Although we believe our estimates are reasonable, we are required to use significant judgment in determining the appropriate amount of valuation allowance recorded against our deferred tax assets.

Our valuation allowance increased by $169 million from December 31, 2022 to December 31, 2023. The increase was primarily related to increases in our deferred tax assets for capitalized research and development expenses and sale of future royalties.

At December 31, 2023, we had federal and state, primarily California, tax net operating loss carryforwards of $242.8 million and $398.8 million, respectively. Our federal tax loss carryforwards are available indefinitely. Our California tax loss carryforwards will begin to expire in 2032. At December 31, 2023, we also had federal and California research and development tax credit carryforwards of $169.7 million and $124.4 million, respectively. Our federal research and development tax credit carryforwards will begin to expire in 2038. Our California research and development tax credit carryforwards are available indefinitely. Our 2023 current tax expense includes a benefit of approximately $3.2 million related to utilization of state tax loss carryforwards, primarily California.

Utilization of the net operating loss and tax credit carryforwards may be subject to an annual limitation due to the ownership change limitations provided by the Internal Revenue Code of 1986, as amended, and similar state provisions. The annual limitation may result in the expiration of net operating losses and credits before utilization.

We analyze filing positions in all U.S. federal, state and foreign jurisdictions where we file income tax returns, and all open tax years in these jurisdictions to determine if we have any uncertain tax positions on any of our income tax returns. We recognize the impact of an uncertain tax position on an income tax return at the largest amount that the relevant taxing authority is more-likely-than not to sustain upon audit. We do not recognize uncertain income tax positions if they have less than 50 percent likelihood of the applicable tax authority sustaining our position.

The following table summarizes our gross unrecognized tax benefits(in thousands):

Included in the balance of unrecognized tax benefits at December 31, 2023, 2022 and 2021 was $0.3 million, $6.2 million and $6.2 million respectively, that if we recognized, could impact our effective tax rate, subject to our remaining valuation allowance.

We estimate that it is reasonably possible that the balance of our gross unrecognized tax benefits may decrease by approximately $7.6 million within the next 12 months due to the lapse of statute of limitations on underlying tax positions primarily related to amortization of certain capitalized state research and development expenditures.

We recognize interest and/or penalties related to income tax matters in income tax expense. During the years ended December 31, 2023, 2022 and 2021, we recognized $0.1 million, $0.8 million and $0.5 million, respectively, of accrued interest and penalties related to gross unrecognized tax benefits.

We are subject to taxation in the U.S. and various state and foreign jurisdictions. U.S. tax years 2020 through 2022 remain open to examination and tax years 2019 through 2022 remain open to examination by major state taxing jurisdictions, primarily California, although net operating loss and credit carryforwards generated prior to these periods may still be adjusted upon examination by the Internal Revenue Service or state tax authorities if they have been used in an open period or are used in a future period.

10. Employment Benefits

We have employee 401(k) salary deferral plans covering all employees. Employees could make contributions by withholding a percentage of their salary up to the IRS annual limits of $22,500 and $30,000 in 2023 for employees under 50 years old and employees 50 years old or over, respectively. We made approximately $7.1 million, $5.6 million and $5.5 million in matching contributions for the years ended December 31, 2023, 2022 and 2021, respectively.

11. Legal Proceedings

From time to time, we are involved in legal proceedings arising in the ordinary course of our business. Periodically, we evaluate the status of each legal matter and assess our potential financial exposure. If we consider the potential loss from any legal proceeding to be probable and we can reasonably estimate the amount, we accrue a liability for the estimated loss. The outcome of any proceeding is not determinable in advance. Therefore, we are required to use significant judgment to determine the probability of a loss and whether the amount of the loss is reasonably estimable. Our assessment of a potential liability and the amount of accruals we recorded are based only on the information available to us at the time. As additional information becomes available, we reassess the potential liability related to the legal proceeding and may revise our estimates.

There are no pending material legal proceedings to which we are a party or of which our property is the subject.

12. Fourth Quarter Financial Data (Unaudited)

The following financial information reflects all normal recurring adjustments, which are, in the opinion of management, necessary for a fair statement of the results of the interim periods. Summarized fourth quarter data for 2023 and 2022 are as follows (in thousands, except per share data).