Seaport Therapeutics, Inc.

1. NATURE OF BUSINESS AND BASIS OF PRESENTATION

Background

Seaport Therapeutics, Inc., and its consolidated subsidiaries, Seaport or the Company, is a clinical-stage therapeutics company focused on inventing and developing medicines for patients with depression, anxiety, and other debilitating neuropsychiatric disorders using the Company's proprietary Glyph™ Platform.

The Company's lead product candidate, GlyphAllo ("Glyph Allopregnanolone"), is a Glyphed oral prodrug of allopregnanolone, an endogenous molecule that has been clinically validated in two third-party trials in the United States for the treatment of postpartum depression, or PPD, a form of major depressive disorder, or MDD, as a rapidly acting antidepressant with anxiolytic and sleep-promoting effects.

The Company's second product candidate, GlyphAgo™ ("Glyph Agomelatine"), is a Glyphed oral prodrug of agomelatine, a clinically validated anxiolytic and antidepressant that is approved for the treatment of generalized anxiety disorder, or GAD, in Australia and MDD in Australia and the European Union, or EU.

The Company is also advancing Glyph2BLSD™ ("Glyph 2-bromo-LSD"), a Glyphed oral prodrug of the non-hallucinogenic LSD analog 2-bromo-LSD, in nonclinical studies for neuropsychiatric and headache disorders with significant unmet need.

There can be no assurance that the Company’s research and development efforts will be successfully completed, that any product candidates developed will obtain necessary government regulatory approval, or that any products, if approved, will be commercially viable. The Company operates in an environment of rapid technological innovation and substantial competition from pharmaceutical and biotechnology companies. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant product revenue from product sales.

Reverse stock split

On April 24, 2026, in anticipation of the Company's initial public offering ("IPO"), the Company effected a 1-for-3.1407 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios of each series of the Company’s convertible preferred stock. The par value and authorized number of shares of common stock and convertible preferred stock were not adjusted as a result. All share and per share amounts for all periods presented in these unaudited condensed consolidated financial statements and notes have been adjusted retroactively, where applicable, to reflect the effect of the reverse stock split.

Initial public offering

During the second quarter of 2026, the Company completed its IPO, in which the Company sold an aggregate of 14,446,658 shares of its common stock at a public offering price of $18.00 per share resulting in aggregate net proceeds of$238.4 million, after deducting underwriting discounts, commissions and other offering expenses.

Immediately prior to the closing of the IPO, the Company's outstanding convertible preferred stock automatically converted into 36,272,475 shares of common stock. Following the closing of the IPO, no shares of convertible preferred stock were outstanding. In connection with the closing of the IPO, the Company's certificate of incorporation was amended and restated to authorize 700,000,000 shares of common stock, including 500,000,000 shares of voting common stock and 200,000,000 shares of non-voting common stock, par value $0.0001 per share and 10,000,000 shares of undesignated preferred stock, par value $0.0001 per share.

Liquidity

In accordance with Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties About an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the condensed consolidated financial statements are issued. The accompanying unaudited condensed consolidated financial statements have been prepared on a going-concern basis, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business.

Since inception, the Company has incurred significant operating losses. During the nine months ended September 30, 2026 and 2025, the Company had a net loss of $114.4 million and $50.7 million, respectively. As of September 30, 2026, the Company had an accumulated deficit of $228.5 million. The Company has not generated any revenue from product sales and does not expect to generate revenue from sales of products in the near term, if at all. The Company expects to incur significant expenses and operating losses for the foreseeable future as it advances its product candidates into and through clinical development and continues to develop additional product candidates. As such, the Company expects research and development and general and administrative costs to continue to increase significantly, including the costs associated with operating as a public company. The Company’s ability to access capital when needed is not assured and, if capital is not available to the Company when, and in the amounts needed, the Company may be required to significantly curtail, delay, or discontinue one or more of its research or development programs or the commercialization of any product candidate, or be unable to expand its operations, or otherwise capitalize on the Company’s business opportunities, as desired, which could materially harm the Company’s business, financial condition, and results of operations.

Prior to the Company's initial public offering, the Company funded its operations with the aggregate gross proceeds of $326.1 million from the Series A and Series B Financings. The Company believes that its existing cash, cash equivalents and investments of$403.8 million as of September 30, 2026, will be sufficient to allow the Company to fund operations for at least twelve months from the date these unaudited condensed consolidated financial statements are issued.

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America, or GAAP. These unaudited condensed consolidated financial statements include the accounts of Seaport Therapeutics, Inc. and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

There have been no significant changes from the significant accounting policies and estimates disclosed in Note 2 of the “Notes to Consolidated Financial Statements” in the audited consolidated financial statements for the year ended December 31, 2025 and notes thereto, included in the Company’s IPO final prospectus filed pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended, or the Securities Act, with the SEC on May 1, 2026.

Unaudited interim financial information

The accompanying unaudited condensed consolidated balance sheet as of September 30, 2026, the condensed consolidated statements of operations and comprehensive loss, and condensed consolidated statements of convertible preferred stock and stockholders' equity (deficit) for the three and nine months ended September 30, 2026 and 2025, and the condensed consolidated statements of cash flows for the nine months ended September 30, 2026 and 2025 are unaudited. The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the December 31, 2025 audited financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the Company's unaudited condensed consolidated financial statements as of September 30, 2026. The results for the nine months ended September 30, 2026 are not necessarily indicative of results to be expected for the year ending December 31, 2026, or for any other subsequent period.

Cash, Cash Equivalents, and Restricted Cash

The Company considers all highly liquid investments that are readily convertible into cash with original maturities of three months or less at the date of purchase to be cash equivalents. The Company invests excess cash primarily in overnight cash sweeps and money market funds which are highly liquid and have high credit ratings. Such investments are subject to minimal credit and market risks. The Company classifies all cash of which use is limited by contractual provisions as restricted cash. Restricted cash is recorded on the condensed consolidated balance sheet within other non-current assets and includes amounts held as a security deposit for a letter of credit in connection with leased facilities and its corporate card program.

The following table summarizes the Company’s cash, cash equivalents, and restricted cash (in thousands):

Deferred Offering Costs

The Company capitalizes certain legal, professional, accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of an equity financing, these costs are recorded as a reduction of the proceeds from the offering, either as a reduction of the carrying value of the convertible preferred stock or in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. Should the in-process equity financing be abandoned or delayed the deferred offering costs would be expensed immediately as a charge to operating expenses in the condensed consolidated statements of operations and comprehensive loss. Upon closing of the Company’s IPO in May 2026, capitalized deferred offering costs of$3.5 million were reclassified within stockholders' equity (deficit) and recorded against the proceeds from the offering. The Company recorded deferred offering costs ofzero and$1.2 million within other non-current assets as of September 30, 2026 and December 31, 2025.

Government Grants

The Company accounts for government awards under ASC 832, Government Assistance. For awards related to income, the Company recognizes grant income when it is probable that the conditions attached to the grant will be satisfied and the grant will be received. The Company elected an accounting policy for the presentation of grant income based on the nature of the underlying government assistance, recorded either as an offset to research and development or other income, which the Company applies consistently to grants of a similar nature.

Net Loss per Share

The Company applies the two-class method when computing net loss per share attributable to common stockholders as the Company has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (loss) available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the undistributed earnings as if all income (loss) for the period had been distributed. The Company considers its convertible preferred stock, prior to conversion upon the Company's IPO, to be participating securities as, in the event a dividend was paid on common stock, the holders of convertible preferred stock would have been entitled to receive dividends on a basis consistent with the common stockholders. There is no allocation required under the two-class method during periods of loss since the participating securities do not have a contractual obligation to share in the losses.

Basic net loss per share is computed by dividing the net loss in each period by the weighted average number of shares of common stock outstanding during such period, excluding potentially dilutive common shares. Diluted net loss per share is computed similarly to basic net loss per share except that the denominator is increased to include the number of additional shares of common stock that would have been outstanding if the potential shares of common stock had been issued and if the additional shares of common stock were dilutive.

Recently Adopted Accounting Pronouncements

In December 2025, the FASB issued ASU 2025-10, Government Grants (Topic 832): Accounting for Government Grants Received by Business Entities, which adds guidance to ASC 832 on the recognition, measurement, and presentation of government grants. In developing the ASU’s recognition and measurement framework, the FASB largely leveraged the guidance in IAS 20, to which many for-profit entities that apply U.S. GAAP have historically analogized when accounting for government grants. The ASU is effective for fiscal years beginning after December 15, 2028, including interim periods within those fiscal years. Early adoption is permitted. The Company early adopted ASU 2025-10 prospectively on January 1, 2026. There wasnot a material impact on the Company’s unaudited condensed consolidated financial statements as a result of this adoption.

Recently Issued Accounting Standards Updates Not Yet Adopted

From time to time, new accounting pronouncements are issued by the FASB, or other standard-setting bodies that are adopted by Seaport as of the specified effective date. The Company qualifies as an ‘‘emerging growth company’’ as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to ‘‘opt out’’ of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and non-public companies, the Company can adopt the new or revised standard at the time non-public companies adopt the new or revised standard and can do so until such time that the Company either (i) irrevocably elects to ‘‘opt out’’ of such extended transition period or (ii) no longer qualifies as an emerging growth company. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for non-public companies. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses, or ASU 2024-03, which is intended to provide more detailed information about specified categories of expenses (purchases of inventory, employee compensation, depreciation, and amortization) included in certain expense captions presented on the statement of operations. The guidance in ASU 2024-03 is effective for fiscal years beginning after December 15, 2026. Early adoption is permitted. The amendments may be applied either (1) prospectively to financial statements issued for periods after the effective date of ASU 2024-03 or (2) retrospectively to all prior periods presented in the financial statements. The Company is currently evaluating the impact that the adoption of ASU 2024-03 may have on its consolidated financial statements and disclosures for fiscal years beginning after December 15, 2026.

3. PREPAID EXPENSES AND OTHER CURRENT ASSETS

Prepaid expenses and other current assets consisted of the following (in thousands):

4. FAIR VALUE MEASUREMENTS

The following table sets forth by level, within the fair value hierarchy, the financial assets and liabilities carried at fair value on a recurring basis (in thousands):

As of September 30, 2026 and December 31, 2025, the Company’s cash equivalents consisted of money market funds which are classified as Level 1 financial assets, as these assets are valued using quoted market prices in active markets without any valuation adjustment and United States treasuries with original maturities less than 90 days, which are classified as Level 2 financial assets.

As of September 30, 2026 and December 31, 2025, the Company's investments consisted of United States treasuries, which are classified as Level 2 financial assets. The Company estimates the fair value of the investments by taking into consideration valuations obtained from third-party pricing sources. As of September 30, 2026 and December 31, 2025, the Company hadno financial liabilities that required fair value measurement. As of September 30, 2026, there wereno securities in an unrealized loss position for more than twelve months.

During the three and nine months ended September 30, 2026 and 2025, there wereno transfers or reclassifications between fair value measurement levels of assets. The carrying amounts reflected in the condensed consolidated balance sheets for prepaid expenses and other current assets, accounts payable, accrued expenses, and other current liabilities approximate fair value due to their short-term nature.

5. INVESTMENTS

The following table summarizes the Company’s investments held (in thousands):

As of September 30, 2026, the Company’s investments were in a net unrealized loss position of $2.0 million. These amounts are included in other comprehensive income (loss) in the condensed consolidated statements of operations and comprehensive loss. The Company determined that there was no material credit risk associated with its investments as of September 30, 2026. As of September 30, 2026, the Company’s investments had remaining maturities oftwo years or less.

As of December 31, 2025, the Company’s investments were in a net unrealized gain position of$0.3 million. These amounts are included in other comprehensive income (loss) in the condensed consolidated statements of operations and comprehensive loss. As of

December 31, 2025, there wereno investments in an unrealized loss position. The Company determined that there was no material credit risk associated with its investments as of December 31, 2025. As a result, the Company didnot record any charges for credit-related impairments for its investments during the year ended December 31, 2025. As of December 31, 2025, the Company’s investments had remaining maturities of two years or less.

6. PROPERTY AND EQUIPMENT, NET

Property and equipment, net consisted of the following (in thousands):

Depreciation expense was$79 thousand and$131 thousand for the nine months ended September 30, 2026 and 2025, respectively.

7. ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES

Accrued expenses and other current liabilities consisted of the following (in thousands):

8. LICENSE AND COLLABORATION AGREEMENTS

Monash License Agreement

In April 2024, PureTech Health exclusively assigned to the Company, and the Company assumed all rights and obligations under a license agreement between PureTech Health and Monash University entered into in August 2017, or the Original License Agreement. In March 2025, the Company entered into an amended and restated license agreement with Monash University, which amended and restated the Original License Agreement, or the Monash License Agreement.

Pursuant to the Monash License Agreement, Monash University grants the Company (i) a worldwide, exclusive, sublicensable license under certain Monash University intellectual property rights, including patent rights related to the Glyph platform, or the Licensed Patents, know-how, and intellectual property stemming from joint research and development activities, for the purpose of developing and commercializing products in all fields with one exception, (ii) a worldwide, non-exclusive, sublicensable license under certain background technology and certain other intellectual property strictly to the extent necessary to exercise the license described in subclause (i) above, and (iii) a first right and an exclusive option to obtain an exclusive license to any invention generated by Monash University outside of the Licensed Patents and pertaining to certain prodrug technology. Additionally, the Company and Monash University agreed to collaborate in conducting research and development activities.

Under the Monash License Agreement, the Company has agreed to use reasonable commercial endeavors to (i) develop at least one Licensed Product, (ii) seek regulatory approval for at least one Licensed Product, and (iii) after receipt of such regulatory approval in the United States or Europe, promote, and develop the sale of at least one Licensed Product in such territory. Monash University agrees to provide reasonable technical assistance and advice based on Monash University’s know-how relating to the technology licensed under the Monash License Agreement. The Company granted Monash University a non-exclusive, perpetual, royalty-free license under the Licensed Patents, related know-how, and intellectual property stemming from joint research and development activities solely for academic, teaching, and non-commercial collaborative research uses, which includes the right to sublicense for non-commercial collaborative research to other academic institutions or non-commercial research entities.

As consideration for the licenses granted by Monash University, the Company is required to pay Monash University: (i) low-single digit royalties with a rate based on net sales per calendar year (subject to certain reductions); (ii) a low-double digit percentage (within the range of 5-15%) of any net income received under a sublicense (subject to a license payment stacking reduction) with the percentage varying based on the development stage of the Licensed Products at the time the sublicense is granted during the term of the Monash License Agreement; (iii) an agreed upon research funding amount to progress mutually agreed research and development or commercialization activities; (iv) a mid-five-figure annual maintenance fee during the term of the agreement commencing on the third anniversary of the execution date of the Original License Agreement until the first commercial sale of a Licensed Product creditable against net income sharing, royalties, and milestone payments; (v) milestone payments in the event of successful development milestones of up to $1.075 million per Licensed Product for the first three Licensed Products; and (vi) milestone payments in the event of successful commercial milestones of up to $7.25 million per Licensed Product for the first three Licensed Products. The Company is also obligated to (a) pay all costs incurred for the prosecution and maintenance of the Licensed Patents and patent filings stemming from collaboration activities and (b) reimburse Monash University for all patent prosecution costs of the Licensed Patents prior to the execution date of the Original License Agreement.

The Monash License Agreement commenced on the execution date of the Original License Agreement and will expire seven years after the last of the Licensed Patents expires, unless terminated earlier. Either party may terminate for due cause, including for material breach and bankruptcy. Monash University may terminate if the Company fails to meet its diligence requirements. Either party may terminate the Monash License Agreement if the Company determines that the activities are no longer commercially viable.

The Monash License Agreement was determined to represent an asset acquisition, as the acquired licenses and intellectual property did not meet the definition of a business. All upfront consideration paid in exchange for the Monash License Agreement was expensed as research and development upon execution of the agreement, as the Licensed Patents and intellectual property was determined to represent in-process research and development with no alternative future use.

Prior to the formation of the Company, PureTech paid $0.2 million in development milestones under the Monash License Agreement. Since the formation of the Company, the Company paid $0.1 million in development milestones under the agreement. No milestones were paid by the Company under the Monash License Agreement during thethree and nine months ended September 30, 2026 and 2025.

Monash Collaboration Agreement and ARPA-H Award

In March 2026, the Advanced Research Projects Agency for Health (“ARPA-H”) granted the Company and Monash University an award for research under the Groundbreaking Lymphatic Interventions and Drug Exploration (“GLIDE”) program (the "Award Agreement"). The Award Agreement provides for total funding of up to $15.2 million, which includes committed funding of $3.5 million for the first phase of research under the award and uncommitted funding of up to $11.7 million for the second phase of the research plan under the award. The funding for the second phase is not currently committed and is subject to mutual agreement by the parties; if exercised, the parties will execute a contract modification at that time. The initial term of the Award Agreement is 48 months. The Award Agreement may be terminated by either party upon 60 days’ written notice, in which case the parties are required to negotiate in good faith to resolve any outstanding matters. Activity under the Award Agreement was immaterial during the three and nine months ended September 30, 2026.

9. CONVERTIBLE PREFERRED STOCK

The Company has issued Series A-1 convertible preferred stock, or the Series A-1 Preferred Stock, Series A-2 convertible preferred stock, or the Series A-2 Preferred Stock, and Series B convertible preferred stock, or the Series B Preferred Stock, and collectively with the Series A-1 Preferred Stock and Series A-2 Preferred Stock, the Preferred Stock.

Immediately prior to the closing of the Company’s IPO on May 1, 2026, pursuant to the reverse stock split and a proportional adjustment to the existing conversion ratios of each series of the Company’s preferred stock as discussed further below, all of the Company’s outstanding shares of convertible preferred stock were converted into an aggregate of 36,272,475 shares of common stock.

In connection with the closing of the IPO, the Company's certificate of incorporation was amended and restated to authorize 10,000,000 undesignated shares of preferred stock, par value $0.0001 per share. There are no shares of undesignated preferred stock outstanding.

Series A-1 and Series A-2 Preferred Stock

In April 2024, the Company issued to PureTech LYT, a wholly owned subsidiary of PureTech,40,000,000 shares of its Series A-1 Preferred Stock, as part of the consideration for the assets contributed to the Company as part of the Asset Transfer Agreement. No value was assigned to the Series A-1 Preferred Stock as it represented consideration paid as part of a common control transaction. See Note 14—Commitments and Contingencies, for further disclosure of the Asset Transfer Agreement.

Concurrently, upon the issuance of the Series A-1 Preferred Stock to PureTech LYT, the Company entered into a Series A-2 Preferred Stock Purchase Agreement, or the Series A-2 Financing, with PureTech LYT and other third-party investors pursuant to which the Company issued and sold 26,342,102 shares of its Series A-2 Preferred Stock at a price of $3.80 per share for gross aggregate proceeds of $100.1 million.

Series B Preferred Stock

In October 2024, the Company entered into a stock purchase agreement with new and existing investors, or the Series B Financing, pursuant to which the Company issued and sold an aggregate amount of 47,578,934 shares of its Series B Preferred Stock at a purchase price of $4.75 per share, for gross aggregate proceeds of $226.0 million.

Upon issuance of the Preferred Stock, the Company assessed the embedded conversion and liquidation features of the securities and determined that such features did not require the Company to separately account for these features.

As of December 31, 2025, Preferred Stock consisted of the following (in thousands, except share and per share amounts):

As of December 31, 2025 the holders of the Preferred Stock had the following rights and preferences:

Voting

The holders of the Preferred Stock are entitled to vote, together with the holders of common stock, as a single class, on all matters submitted to the stockholders for a vote and are entitled to the number of votes equal to the number of shares of common stock into which the Preferred Stock would convert on the record date for determination of stockholders entitled to vote. The holders of the Preferred Stock generally vote together as a single class with holders of common stock except that, (i) the holders of Series A-1 Preferred Stock, exclusively and voting together as a separate class on an as converted basis, shall be entitled to elect two (2) directors of the Company, each, a Series A-1 Director, (ii) the holders of record of the shares of Series A-2 Preferred Stock, exclusively and voting together as a separate class on an as converted basis, shall be entitled to elect two (2) directors of the Company, each, a Series A-2 Director, (iii) the holders of record of the shares of Series B Preferred Stock, exclusively and voting together as a separate class on an as converted basis, shall be entitled to elect one (1) director of the Company, or the Series B Director and, together with the Series A-1 Directors and Series A-2 Directors, each, a Preferred Director.

Further, a majority vote of the holders of the Company's Preferred Stock is required to, among others, liquidate or dissolve the Company, amend the certificate of incorporation or bylaws, reclassify common stock or establish another class of capital stock, create shares that would rank senior to or authorize additional shares of Preferred Stock, declare a dividend or make a distribution, or change the authorized number of directors constituting the board of directors.

Dividends

The holders of the Preferred Stock are entitled to participate in any dividends payable to common stockholders on an as converted basis and have priority over the payment of dividends to holders of common stock.

In the case of a dividend on common stock or any class of stock that is convertible into common stock, the dividend per share of Preferred Stock would equal the product of (A) the dividend payable on each share of such class or series as if all shares of such class or series had been converted into common stock and (B) the number of shares of common stock issuable upon conversion of such share of Preferred Stock. In the case of a dividend on any class or series that is not convertible into common stock, the dividend per share of Preferred Stock would be determined by (A) dividing the amount of dividend payable on each share of such class or series of capital stock by the original issue price of such class or series and (B) multiplying such fraction by the original issue price of the applicable class or series of Preferred Stock.

Conversion

Each outstanding share of Preferred Stock is convertible, at any time, at its holder’s discretion, and without the payment of additional consideration, into such whole number of fully paid, non-assessable shares of common stock, at the applicable conversion ratio then in effect. The conversion price for each share of Preferred Stock shall initially be equal to the original issuance price for such series of Preferred Stock and is subject to standard anti-dilutive adjustments for share splits and similar transactions. In the event certain conditions are not met prior to March 31, 2026, the conversion price of the Series B Preferred Stock will be reduced to $3.80. In July 2025, the Company satisfied the applicable condition, thereby eliminating the conversion price reduction contingency.

Each outstanding share of Preferred Stock shall automatically be converted into fully-paid, non-assessable shares of common stock upon the earliest to occur of (i) the consummation of a qualified initial public offering at a public offering price of at least $5.70 per share, in a firm commitment resulting in at least $100.0 million of gross proceeds or (ii) the date specified by vote or written consent of the holders of at least a majority of the outstanding shares of the Preferred Stock, voting together as a single class on an as-converted basis, and the holders of a majority of the outstanding shares of Series A-2 Preferred Stock and Series B Preferred Stock, which majority must include at least one new investor from the Series B Financing that holds at least 2,100,000 shares of Series B Preferred Stock, voting together as a single class on an as-converted basis, or the Requisite Holders, and the holders of at least 65% of the then-outstanding shares of Series B Preferred Stock, or the Series B Majority. All outstanding convertible preferred stock was converted into common stock immediately prior to the closing of the Company’s IPO.

There shall be no adjustment in the conversion price of the Preferred Stock as a result of the issuance or deemed issuance of additional shares of the Company’s common stock if the Company receives written notice from the holders of at least a majority of the then outstanding shares of Preferred Stock, voting together as a single class, and, solely in the respect of an adjustment in the conversion price of the Series B Preferred Stock, the Series B Majority, agreeing that no such adjustment shall be made as the result of the issuance or deemed issuance of additional shares of the Company’s common stock.

Liquidation

In the event of any voluntary or involuntary liquidation, dissolution, or winding up of the Company, or upon the occurrence of a Deemed Liquidation Event (as defined below), the holders of shares of Preferred Stock then outstanding shall be entitled, on a pari passu basis among the series of Preferred Stock, to be paid out of the assets or funds of the Company available for distribution to stockholders before any payment is made to the holders of common stock. The holders of Preferred Stock are entitled to an amount per share equal to the greater of (i) the original issue price for such series, plus any dividends declared but unpaid thereon, or (ii) the amount that would have been payable had all shares of each series of Preferred Stock been converted into common stock immediately prior to such liquidation, dissolution, winding up or Deemed Liquidation Event. After the payment in full of the Preferred Stock preference amount, the remaining assets of the Company available for distribution to stockholders shall be distributed among the holders of common stock on a pro rata basis.

Each of the following events shall be considered a “Deemed Liquidation Event,” unless the Requisite Holders, elect otherwise; a merger, consolidation, statutory conversion, transfer, domestication, continuance involving the Company or a subsidiary, or a sale, lease, or transfer of substantially all of the assets of the Company.

Redemption

The Preferred Stock did not have any redemption rights, except for the contingent redemption upon the occurrence of a Deemed Liquidation Event.

10. COMMON STOCK

The voting, dividend, and liquidation rights of the holders of the Company’s common stock were, prior to the conversion of all outstanding preferred shares into common stock upon the Company's IPO, subject to and qualified by the rights, powers, and preferences of the holders of the Preferred Stock set forth above. Each share of common stock entitles the holder toone vote on all matters submitted to the stockholders for a vote. The holders of common stock are entitled to receive dividends, if any, as declared by the Company’s board of directors (the "Board"). As of September 30, 2026, no dividends have been declared or paid.

As of September 30, 2026, the Company had authorized 500,000,000 shares of voting common stock and 200,000,000 shares of non-voting common stock, par value $0.0001 per share, of which 53,530,550 shares of voting common stock were issued and outstanding. There areno shares ofnon-voting common stock outstanding.

11. STOCK-BASED COMPENSATION

2024 Equity Incentive Plan

The Company’s 2024 Equity Incentive Plan, as amended (the “2024 Plan”), provided for the Company to sell or issue common stock or restricted common stock, and other awards as determined by the Board could be granted to employees, non-employees and directors of the Company. As of the effective date of the 2026 Equity Incentive Plan (the “2026 Plan”), there were no shares remaining available for future issuance under the 2024 Plan. Any options or other awards outstanding under the 2024 Plan remain outstanding and effective. The remaining shares reserved for issuance under the 2024 Plan ceased to be available for issuance at the time that the 2026 Plan became effective.

Subsequent to the effectiveness of the 2026 Plan, the shares of common stock underlying any awards under the 2024 Plan that are forfeited, canceled, reacquired by the Company prior to vesting, satisfied without the issuance of stock or otherwise terminated (other than by exercise) and shares withheld upon exercise of an option or settlement of an award to cover the exercise price or tax withholding will be added to the shares of common stock available for issuance under the 2026 Plan.

2026 Equity Incentive Plans

In January 2026, the Board and the Company's stockholders adopted and approved the 2026 Plan, which became effective on the date that the registration statement on Form S-1 for the Company's IPO was declared effective by the SEC. The 2026 Plan initially reserved 6,020,000 shares of common stock for future issuances and is subject to automatic increases in the number of shares of common stock reserved for future issuances in accordance with the evergreen provisions in the 2026 Plan. The shares reserved for future issuance under the 2024 Plan ceased to be available for issuance at the time the 2026 Plan became effective. Any shares underlying outstanding stock awards granted under the 2024 Plan that subsequently expire or are repurchased, forfeited, canceled, or withheld will return to the 2026 Plan and be reserved and available for issuance.

On the effective date of the Company's registration statement the Company granted 2,477,978 fully vested equity awards under the 2026 Plan to an executive officer and a director pursuant to provisions designed to maintain their aggregate ownership at 12.5%, and recognized $32.2 million of non-cash stock-based compensation expense related to these awards. These ownership maintenance provisions expired upon effectiveness of the registration statement, and no additional awards will be granted pursuant to them. In addition, the Company's IPO triggered the accelerated vesting of 687,816 equity awards held by an executive officer and a director that were originally granted under the 2024 Plan, resulting in the recognition of $2.1 million of non-cash stock-based compensation expense.

In April 2026, the Board and the Company's stockholders adopted and approved the 2026 Employee Stock Purchase Plan (the "2026 ESPP"), which became effective the date that the registration statement on Form S-1 for the Company's IPO was declared effective by the SEC. The 2026 ESPP initially reserved 510,000 shares of common stock for future issuance and is subject to automatic increases in the number of shares of common stock reserved for future issuances in accordance with the evergreen provisions in the 2026 ESPP. As of September 30, 2026, the Company has issuedno shares under the 2026 ESPP.

Stock options issued under the plans generally vest over four years, with 25% vesting on the first anniversary and the rest in equal monthly installments thereafter, and may be subject to accelerated vesting. Performance-based options vest inthree annual installments that are contingent upon the achievement of the Company’s annual goals.

Stock Option Activity

The following is a summary of the Company’s stock option award activity under the 2024 Plan and 2026 Plan during thenine months ended September 30, 2026:

The table above excludes 116,428 performance-based options which have an exercise price of $7.39 per share, that were approved to be issued by the Company’s Board of Directors in December 2024, but have not yet been deemed granted from an accounting perspective as of September 30, 2026. During the nine months ended September 30, 2026,76,256 performance-based options were determined to be granted from an accounting perspective and the Company recorded stock compensation expense of $0.6 million.

The Company utilized the Black-Scholes option-pricing model for estimating the fair value of the stock options issued under the plans on each grant date. The following table presents the ranges of assumptions used by the Company in the Black-Scholes option-pricing model during the nine months ended September 30, 2026 and 2025:

The weighted-average grant date fair value of options granted during the nine months ended September 30, 2026 and 2025 was $12.04 and$5.66 per share, respectively. The aggregate intrinsic value is calculated as the difference between the exercise price and the fair value of the Company’s common stock as of each period end or exercise date.

As of September 30, 2026, there was $24.4 million in unrecognized stock-based compensation expense associated with issued and outstanding service-based stock options, which is expected to be recognized over a weighted-average period of 2.4 years.

2024 Plan Restricted Stock Awards

The Company has granted restricted stock awards to certain members of the Company’s Board of Directors and Chief Executive Officer. Of the total 1,990,001 restricted stock awards granted: (i)796,000 have service-based vesting in equal monthly installments over athree-year period, of which 50% of the unvested amount was subject to accelerated vesting upon the close of the Series B Financing and 50% of any unvested amounts is subject to future acceleration upon the close of an initial public offering; and (ii)1,194,001 have performance based vesting which vested in full upon the close of the Series B Financing. The Company completed its IPO in May 2026, upon which all unvested restricted stock awards vested in full.

The following is a summary of the Company’s restricted stock award activity during thenine months ended September 30, 2026:

No restricted stock awards were granted during thenine months ended September 30, 2026 and 2025. The total fair value of the restricted stock awards that vested during the nine months ended September 30, 2026 and 2025 was $0.5 million and $0.3 million, respectively. The total stock-based compensation associated with the restricted stock awards waszero and$0.5 million during thethree and nine months ended September 30, 2026, respectively, and$0.1 million and$0.3 million during thethree and nine months ended September 30, 2025, respectively. As of September 30, 2026, there wasno unrecognized stock-based compensation expense associated with issued and outstanding restricted stock awards.

Stock-Based Compensation Expense

The following table represents stock-based compensation expense recorded in the Company’s condensed consolidated statements of operations and comprehensive loss (in thousands):

12. INCOME TAXES

The Company's effective tax rates were (0.5)% and (0.8)% for thethree and nine months ended September 30, 2026, respectively; and (0.4)% and (0.5)% for thethree and nine months ended September 30, 2025, respectively. The effective tax rate in 2026 differs from 2025 primarily due to tax expense recorded in Australia. The income tax provision and effective tax rate are driven primarily by a valuation allowance in the United States, partially offset by income tax expense recorded for Australian operations. The Australian subsidiary is profitable due to its research and development tax credit and transfer pricing agreement with Seaport Therapeutics, Inc. and is subject to income tax expense.

The Company maintains a valuation allowance on the majority of its deferred tax assets, and it has concluded that it is more likely than not that the deferred tax assets will not be utilized.

13. LEASES

In October 2024, the Company entered into an operating lease for office space in Boston, Massachusetts, which commenced in December 2024 and has an initial lease term that continues through October 20, 2030, with no options to extend. In conjunction with entering into the lease, the Company paid a security deposit of $0.2 million in the form of a letter of credit, which is recorded as restricted cash within other non-current assets on the Company’s condensed consolidated balance sheets as of September 30, 2026 and December 31, 2025.

In December 2024, the Company entered into a laboratory lease agreement with a third party for lab space located in Boston, Massachusetts. The lease commenced in January 2025 and was for an initial term of 24 months from the commencement date. In March 2026, the Company exercised itsoption to extend the lease for an additional 12 months. The modification resulted in an increase to the operating lease right of use asset and lease liability of $0.6 million.

14. COMMITMENTS AND CONTINGENCIES

Legal Matters

The Company, from time to time, may be involved with lawsuits arising in the ordinary course of business. The Company is not involved in any pending legal proceedings that it believes could have a material adverse effect on its financial condition, results of operations, or cash flows.

Contracts

The Company enters into contracts in the normal course of business with various third parties for nonclinical research studies, clinical trials, testing, manufacturing, and other services. These contracts generally provide for termination upon notice and are cancelable without significant penalty or payment, and do not contain any minimum purchase commitments.

License and Other Agreements

The Company is obligated to make fixed and contingent payments under the Asset Transfer Agreement and Monash License Agreement. See Note 8—License and Collaboration Agreements, for further disclosureof the Monash license agreement.

The Asset Transfer and Series A Financing

On April 8, 2024, or the Asset Transfer Date, the Company entered into an asset transfer agreement, as amended in December 2025, or the Asset Transfer Agreement with PureTech Health LLC, or PureTech Health, and PureTech LYT, pursuant to which PureTech Health and PureTech LYT, agreed to contribute, convey, assign, transfer, and deliver to the Company all of its right, title, and interest in, to and under the assets related to its Glyph technology and products, or the Asset Transfer. As consideration, the Company issued to PureTech LYT 40,000,000 shares of its Series A-1 convertible preferred stock and 302,161 shares of its common stock on the Asset Transfer Date, and also agreed to contingent payments to PureTech upon successful development and commercialization of products developed using the Glyph platform, each of which is referred to as a Seaport Glyph Product, including milestone payments of up to an aggregate of $10.0 million for the first product covered by assets transferred through the Asset Transfer Agreement, or the Seaport Glyph Product, of $2.0 million for the first patient dosed in the first phase 3 clinical trial, $4.0 million for the first commercial sales in the United States, $2.0 million for the first commercial sale in a major European market, and $2.0 million for the first commercial sale in Japan, and for each subsequent Seaport Glyph Product, the Company has agreed to make milestone payments of $1.0 million for the first patient dosed in the first phase 3 clinical trial, $2.0 million for the first commercial sale in the United States, $1.0 million for the first commercial sale in a major European market, and $1.0 million for the first commercial sale in Japan. In addition, the Company is obligated to pay royalties between 3% and 5% on the annual net sales of each Seaport Glyph Product as follows: less than $500 million:3%; $500 million to $1 billion:3.5%; $1 billion to $2.5 billion:4%; $2.5 billion to $3.5 billion:4.5%; $3.5 billion or greater:5% and a percentage of net income generated by the Company from third parties on any products licensed under the Glyph intellectual property which was transferred as part of the Asset Transfer Agreement.

Guarantees and Indemnification

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners, and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with all members of the board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any claims under indemnification arrangements that could have a material effect on its financial position, results of operations, or cash flows, and it hasnot accrued any liabilities related to such obligations in itscondensed consolidated financial statements as of September 30, 2026 and December 31, 2025 and for the nine months ended September 30, 2026 and 2025.

Leases

See Note 13—Leases, for information related to the Company’s lease obligations.

15. SEGMENTS

The Company hasone operating and reportable segment focused on inventing and developing novel medicines for patients with depression, anxiety, and other debilitating neuropsychiatric disorders using the Company's proprietary Glyph™ Platform.

The chief operating decision-maker, or CODM, manages the Company’s operations on a consolidated basis, and assesses performance based on consolidated net loss that is reported on the condensed consolidated statements of operations and comprehensive loss. The CODM makes decisions about allocating resources and assessing performance for the entire company. The measure of segment assets is reported on the condensed consolidated balance sheet as total consolidated assets.

The following table presents certain significant segment expenses that are regularly provided to the CODM (in thousands):

(1)

Other general and administrative expenses include professional fees, facilities, depreciation, IT, and other expenses.

(2)

Other segment items include interest income, net, research and development tax credit, income tax provision, and other income (expense), net.

16. NET LOSS PER SHARE

Under the two-class method, basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. The net loss available to common stockholders was not allocated to the Preferred Stock as the holders did not have a contractual obligation to share in losses. Diluted net loss per share is the same as basic net loss per share for the three and nine months ended September 30, 2026 and 2025, presented since the effects of any potentially dilutive securities would be antidilutive given the net loss of the Company.

Basic and diluted net loss per share is calculated as follows (in thousands except share and per share amounts):

For accounting purposes, the computation of basic weighted-average common shares outstanding excludes all shares of unvested restricted common stock as such shares are not considered outstanding. See Note 11—Stock-Based Compensation, for more information.

The following outstanding potentially dilutive securities have been excluded from the calculation of diluted net loss per share attributable to common stockholders, as their effect is antidilutive:

(1)

The table above excludes the performance-based options that have not been deemed granted from an accounting perspective. See Note 11—Stock-Based Compensation, for more information.

17. RELATED PARTIES

During the nine months ended September 30, 2026, the Company incurred immaterial expenses from PureTech under the transition services agreement, or the TSA, related to general and administrative expenses. During the nine months ended September 30, 2025, the Company incurred $0.4 million of expenses from PureTech under the TSA, primarily related to research and development expenses.