Alto Neuroscience, Inc.

Condensed Consolidated Balance Sheets (Unaudited)

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited)

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Unaudited)

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Unaudited)

Condensed Consolidated Statements of Cash Flows (Unaudited)

(in thousands)

1. Description of the Business

Alto Neuroscience, Inc. (the “Company” or “Alto”) was incorporated in Delaware on March 25, 2019. The Company maintains its headquarters in Mountain View, California. The Company hasone wholly-owned subsidiary in Australia that was formed during 2020 to conduct clinical trials.

Alto is a clinical-stage biopharmaceutical company with a mission to redefine psychiatry by leveraging neurobiology to develop personalized and highly effective treatment options. Through insights derived from the Company’s scalable and proprietary Precision Psychiatry Platform, the Company aims to discover brain-based biomarkers to better identify which patients are more likely to respond to its novel product candidates. The Company’s current pipeline consists ofseven clinical-stage assets addressing high-need therapeutic areas, focusing on major depressive disorder (“MDD”), bipolar depression (“BPD”), treatment resistant depression (“TRD”), and schizophrenia.

Liquidity and Capital Resources

The Company has incurred significant operating losses since inception and has relied upon equity financings to fund its operations. At June 30, 2025, the Company had an accumulated deficit of approximately $171.3 million. As the Company continues to incur losses, its transition to profitability will depend on the successful development, approval and commercialization of product candidates and on the generation of sufficient revenues to support its cost structure. No assurance can be provided that the Company will ever be profitable, and unless or until it becomes profitable, the Company will need to continue to raise additional capital.

In February 2024, the Company completed its initial public offering (“IPO”) of its common stock. The Company issued and sold 9,246,000 shares of common stock at a public offering price of $16.00 per share, which included 1,206,000 shares sold pursuant to the exercise of the underwriters’ option to purchase additional shares, and received net proceeds of $133.0 million after deducting underwriting discounts and commissions and other offering costs. Upon completion of the IPO, all outstanding shares of the Company’s outstanding preferred stock converted into an aggregate of 13,664,261 shares of common stock. In addition, the IPO resulted in the net exercise and conversion of all outstanding Series A Preferred Stock Warrants for an aggregate of 72,631 shares of common stock.

2. Summary of Significant Accounting Policies and Basis of Presentation

Basis of Presentation

The accompanying interim condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”), and include the accounts of Alto and its wholly-owned subsidiary. All intercompany transactions and balances have been eliminated in consolidation.

The interim condensed consolidated financial statements are unaudited and have been prepared on the same basis as the audited annual financial statements and, in management’s opinion, include all adjustments consisting of only normal recurring adjustments necessary for the fair statement of the Company’s financial position as of June 30, 2025 and its results of operations and statements of equity for thethree and six months ended June 30, 2025 and 2024 and cash flows for thesix months ended June 30, 2025 and 2024. The results of operations for the three and six months ended June 30, 2025 are not necessarily indicative of the results to be expected for the full fiscal year or any other period.

Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements and the related notes thereto for the year ended December 31, 2024 included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 20, 2025 (the “Annual Report”).

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results may differ materially from those estimates. The most significant estimates and assumptions in the Company’s condensed consolidated financial statements relate to the determination of the volatility of its common stock (as an input for calculating stock-based compensation and warrants), estimating accrued or prepaid research and development expenses, and the valuation of the preferred stock warrant liability. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected.

Significant Accounting Policies

The Company’s significant accounting policies used in the preparation of these condensed consolidated financial statements for thethree and six months ended June 30, 2025 are consistent with those discussed in Note 3 to the consolidated financial statements in the Annual Report.

Recently Issued Accounting Pronouncements

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. The standard expands the disclosure requirements for income taxes, specifically related to the rate reconciliation and income taxes paid. The standard will be effective starting in annual periods beginning after December 15, 2024, with early adoption permitted. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statement disclosures.

In November 2024, the FASB issued ASU No. 2024-03, Income Statement – Reporting Comprehensive Income – Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses, which expands disclosures about specific expense categories presented on the face of the income statement. The standard is effective for annual reporting periods beginning after December 15, 2026 and interim reporting periods beginning after December 15, 2027. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statements.

In November 2024, the FASB issued ASU No. 2024-04, Debt – Debt with Conversion and Other Options (Subtopic 470-20): Induced Conversions of Convertible Debt Instruments, which affects entities that settle convertible debt instruments for which the conversion privileges were changed to induce conversion. The standard is effective for annual reporting periods beginning after December 15, 2025, and interim reporting periods within those annual reporting periods. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statements.

3. Balance Sheet Components

Prepaid Expenses and Other Current Assets

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

Property and Equipment, Net

Property and equipment, net are as follows (in thousands):

During thethree and six months ended June 30, 2025, the Company recorded depreciation and amortization expense of $0.1 million and $0.3 million, respectively. During thethree and six months ended June 30, 2024, the Company recorded depreciation and amortization expense of $0.1 million and $0.2 million, respectively.

Accrued Expenses and Other Current Liabilities

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

4. Debt

K2 HealthVentures LLC Loan Agreement

On December 16, 2022, the Company entered into a Loan and Security Agreement (the “Original Loan Agreement”) with K2 HealthVentures LLC as a lender, the other lenders party thereto (collectively, the “Lender”), K2 HealthVentures LLC, as administrative agent for Lender (the “Administrative Agent”), and Ankura Trust Company, LLC, as collateral agent for the Lender. Pursuant to the terms of the Original Loan Agreement, the Lender agreed to make available to the Company term loans (each, collectively, the “Term Loan”) in an aggregate principal amount of up to $35.0 million. As of December 31, 2024, the Company had drawn a principal amount of $10.0 million. The Lender’s commitment to make available additional Term Loans under the Original Loan Agreement expired without being drawn on January 1, 2025. The Original Loan Agreement had a Term Loan maturity date of December 1, 2026 (the “Original Term Loan Maturity Date”).

On January 13, 2025, the Company entered into an amendment to the Original Loan Agreement (the “Amendment” and the Original Loan Agreement as amended thereby, the “Amended Loan Agreement”) to, among other things, extend the Original Term Loan Maturity Date and increase the maximum available amount of term loans. The Amended Loan Agreement provides for term loans in an aggregate principal amount of up to $75.0 million, consisting of:

•a first tranche term loan of $20.0 million;

•second tranche term loans of up to $30.0 million in the aggregate available at the Company’s request until December 15, 2025, subject to certain time-based, clinical milestones; and

•third tranche term loans of up to $25.0 million in the aggregate available at the Company’s request subject to the Lender’s approval.

The Company drew $20.0 million upon entry into the Amendment (approximately $10.0 million of which was used to refinance obligations under the Original Loan Agreement and pay fees and expenses incurred in connection with the Amendment). A portion of the second tranche term loans is tied to the timing of data from the Company’s Phase 2b study of ALTO-300; based on expected timing of top line data for this study, the Company anticipates that $20.0 million of the second tranche term loans will expire without being drawn.

The Amended Loan Agreement has a Term Loan maturity date of January 1, 2029 (the “Amended Term Loan Maturity Date”). The Amended Loan Agreement provides for an interest only period until January 1, 2027, following which the Term Loan shall be repaid in equal monthly payments through the Amended Term Loan Maturity Date.

The Term Loan bears interest at (i) a variable per annum cash pay rate equal to the Prime Rate plus 1.45% (subject to a floor of 8.45% per annum) and (ii) a fixed per annum paid-in-kind rate equal to 1.0%. Interest is due and payable monthly in arrears. Upon final payment or prepayment of the Term Loan, the Company is required to pay a final payment equal to 5.95% of the amount borrowed.

The Amended Loan Agreement was accounted for as a debt extinguishment, as the new loan was considered substantially different from the original loan. The Company recognized debt issuance costs and discount upon issuance of $2.0 million within Term Loan, non-current on its condensed consolidated balance sheet and recorded a loss on debt extinguishment of $0.7 million, which was recorded within loss on debt extinguishment in its condensed consolidated statement of operations and comprehensive loss forthe six months ended June 30, 2025.

Fees

Under the terms of the Original Loan Agreement, the Company was obligated to pay a final fee equal to 6.25% of the aggregate amount of the term loans funded thereunder (the “Original Exit Fee”) upon the earliest of (i) the Original Term Loan Maturity Date, (ii) the acceleration of the Term Loan, and (iii) the prepayment of the Term Loan. The Company was also obligated to pay the Lender a one-time facility fee of $0.2 million (“Original Facility Fee”) on the initial closing date. The Original Exit Fee of $0.6 million and Original Facility Fee of $0.2 million were recorded as debt discount, and were being accreted using the effective interest method within interest expense in the consolidated statements of operations and comprehensive loss. The Company’s obligation to pay the Original Exit Fee remains outstanding, and the timing for payment thereof was unaffected by, and reaffirmed in connection with, the Amendment.

The Company was obligated to pay the Lender a one-time facility fee of $0.3 million upon entry into the Amendment. The Company is also obligated to pay a funding fee on each third tranche term loan in an amount equal to the sum of 0.5% multiplied by the amount of such third tranche term loan, if and when funded. Under the terms of the Amended Loan Agreement, the Company is obligated to pay a final fee equal to 5.95% of the aggregate amount of the Term Loan funded thereunder (the “Amended Exit Fee”) upon the earliest of (i) the Amended Term Loan Maturity Date, (ii) the acceleration of the Term Loan, and (iii) the prepayment of the Term Loan. As of June 30, 2025, the amount owed under the Amended Exit Fee is equal to $1.2 million. The Original Exit Fee and the Amended Exit Fee have been fully accrued and recorded as debt discount as of the closing date of the Amendment and will be accreted using the effective interest method within interest expense in the consolidated statement of operations and comprehensive loss.

The Company has the option to prepay all, but not less than all, of the Term Loan prior to the Amended Term Loan Maturity Date, which would require that the Company pay the Lender a prepayment penalty fee based on a percentage of the outstanding principal balance and the funding date of the individual tranches thereunder. As to each such tranche under the Term Loan, such fee shall be equal to 3% if the payment occurs on or before 24 months after the funding date of such tranche,2% if the prepayment occurs more than 24 months after, but on or before 36 months after the funding date of such tranche, or 1% if the prepayment occurs more than 36 months after the funding date of such tranche. No prepayment penalty fee is required if the applicable tranche is prepaid within six months prior to the Amended Term Loan Maturity Date or refinanced with the Lender.

Other Terms

Following an initial period with no financial covenants, beginning January 1, 2026, the Company must maintain, at all times, a cash runway of at least 5 months, provided that this covenant will be waived during any period in which the Company’s market capitalization exceeds $700.0 million.

The Company’s obligations under the Amended Loan Agreement are secured by a first priority security interest in substantially all of its assets (with an exclusion for intellectual property). The Amended Loan Agreement contains customary represent ations and warranties, and also includes customary events of default, including payment default, breach of covenants, change of control, and material adverse effects. The Amended Loan Agreement restricts certain activities, such as disposing of the Company’s business or certain assets, incurring additional debt or liens or making payments on other debt, making certain investments and declaring dividends, acquiring or merging with another entity, engaging in transactions with affiliates or encumbering intellectual property, among others.

Upon the occurrence of an event of default, a default interest rate of an additional 5% per annum may be applied to the outstanding loan balances, and the Lender may declare all outstanding obligations immediately due and payable and exercise all of its rights and remedies as set forth in the Amended Loan Agreement and under applicable law.

Warrants

In connection with the Original Loan Agreement, the Company issued to the Lender a warrant (the “Original Warrant”), which Original Warrant is exercisable for 35,773 shares of the Company’s common stock and expires on December 15, 2032. In connection with the Amendment, the Original Warrant was amended and restated (the “Amended and Restated Warrant”) to reduce the exercise price from $10.49 to $3.71 per share (the “Exercise Price”). The incremental value associated with this modification was immaterial, and was included as part of the determination of the loss on debt extinguishment, with a corresponding increase in additional paid-in capital during the six months ended June 30, 2025. Further, in connection with the Amendment, the Company issued an additional warrant (the “New Warrant”, together with the Amended and Restated Warrant, the “Warrants”) to purchase a number of shares of the Company’s common stock calculated as follows: (a) (i)0.025, multiplied by (ii) the aggregate principal amount of the term loans actually funded under the Amended Loan Agreement, divided by (b) the Exercise Price. The New Warrant expires on January 13, 2035.

As of June 30, 2025 the New Warrant allowed for the purchase of 134,691 shares of the Company’s common stock. If the Company draws down on additional tranches of the Term Loan, the number of shares available for purchase by the Lender under the New Warrant would increase. The Company determined the estimated fair value of the New Warrant at the date of issuance to be $0.5 million, which was included as part of the determination of the loss on debt extinguishment, with a corresponding increase in additional paid-in capital. As of the date of the issuance, significant assumptions include an expected life of 10 years, a risk-free rate of 4.79% and an expected volatility of 89.47%. See Note 10 for additional information regarding the New Warrant.

Loan Conversion Feature

Under the terms of the Amended Loan Agreement, the Lender may, at its option, elect to convert up to $9.0 million of the then outstanding Term Loan (the “Conversion Amount”) ($4.0 million of which was reflected in the Original Loan Agreement and $5.0 million of which is reflected in the Amended Loan Agreement) into shares of the Company’s common stock (the “Conversion Shares”). The number of shares to be issued upon conversion is determined by dividing (a) the portion of the term loan amount converted, by (b) the Applicable Conversion Price. Applicable Conversion Price means (i) with respect to any conversion of up to $4.0 million of the Conversion Amount, $10.49, and (ii) with respect to any conversion of the remaining $5.0 million of the Conversion Amount, $4.83, in each case subject to certain adjustments set forth in the Amended Loan Agreement. The Company determined that the embedded conversion option is not required to be separated from the Term Loan. The embedded conversion option meets the derivative accounting scope exception since the embedded conversion option is indexed to the Company’s own common stock and qualifies for classification within stockholders’ equity.

Interest Expense and future repayments

The Company recorded interest expense at a weighted average rate of 12.96% related to the Loan Agreement for both the three and six months ended June 30, 2025. The Company recorded interest expense at a weighted average rate of 10.70% related to the Loan Agreement for both the three and six months ended June 30, 2024. During the three and six months ended June 30, 2025, the Company recorded interest expense of $0.6 million and $1.2 million, respectively. During the three and six months ended June 30, 2024, the Company recorded interest expense of $0.4 million and $0.7 million, respectively.

Future principal debt payments and Exit Fee of the term loan funded as of June 30, 2025 are as follows (in thousands):

The Wellcome Trust Limited Convertible Grant Agreement

In July 2024, the Company entered into a convertible loan agreement (the “Convertible Grant Agreement”) with The Wellcome Trust Limited (“Wellcome”). The Convertible Grant Agreement provides for an unsecured convertible loan (the “Convertible Loan”) from Wellcome of up to approximately $11.7 million, payable to Alto insix tranches, of which up to $2.0 million could be funded upon the execution of the Convertible Grant Agreement and the remainder of which will be funded upon the completion of certain milestones as set forth in the Convertible Grant Agreement. As of June 30, 2025, the Company has drawn down the entirety of the $2.0 million execution tranche and will continue to access the loan as needed as the ALTO-100 study in bipolar depression progresses. Interest will accrue at an annual rate equal to the Sterling Overnight Index Rate plus 2%, subject to potential adjustment if such annual interest rate equals or exceeds 9% at any time. Proceeds from the Convertible Loan may be used by the Company solely to advance development of ALTO-100 in bipolar depression. The Convertible Grant Agreement also includes customary covenants, representations and warranties, including with respect to the conduct of the Company’s Phase 2b clinical trial evaluating ALTO-100 in patients with bipolar depression and certain information and audit rights of Wellcome in connection therewith, as well as with respect to the Company’s efforts to develop and exploit ALTO-100.

At any time after the second anniversary of the effective date of the Convertible Grant Agreement or in connection with an event of default, Wellcome has the right, at its election, to convert some or all of the Convertible Loan into shares of the Company’s common stock at a price per share equal to a 20% discount to thethirty-day volume-weighted average price of Common Stock on the New York Stock Exchange at the date of such conversion. The Convertible Grant Agreement provides that in no event shall the aggregate number of shares of Common Stock issued pursuant to conversion of the Convertible Loan exceed 5,363,326, which is equal to 19.9% of the number of shares of Common Stock outstanding as of the date of the Convertible Grant Agreement. At any time after the fifth anniversary of the effective date of the Convertible Grant Agreement or in connection with an event of default, Wellcome may require repayment of the Convertible Loan in full, together with accrued interest, to the extent not converted as described above.

Future principal debt payments of the Convertible Grant Agreement funded as of June 30, 2025 are as follows (in thousands):

The Company assessed the terms and features of the Convertible Grant Agreement and determined that the Company was eligible to elect the fair value option under ASC 825, Financial Instruments. The Convertible Grant Agreement contains various embedded features and the election of the fair value option allowed the Company to bypass analysis of potential embedded derivatives and further analysis of bifurcation of any recognized financial liabilities. Under the fair value option, the financial liability is initially measured at its fair value on the issue date and subsequently remeasured at estimated fair value on a recurring basis at each reporting date. Changes in the fair value of the Convertible Grant Agreement, which include accrued interest, if any, are recorded as a componentof other, net or within other comprehensive income (loss) in the condensed consolidated statements of operations and comprehensive loss. The Company has not elected to present interest expense separately from changes in fair value and therefore will not present interest expense associated with the Convertible Grant Agreement. Any changes in fair value caused by instrument-specific credit risk are presented separately in other comprehensive income or loss.

The Company determined the initial fair value of the Convertible Grant Agreement using a probability-weighted income approach and recorded the loan at the fair value of the initial draw down of $1.3 million during 2024 and the second draw down of $0.8 million during the three months ended June 30, 2025 in the condensed consolidated balance sheet at their respective issuance dates. The Company remeasured the fair value of the Convertible Grant Agreement as of June 30, 2025 to be $2.0 million using a probability-weighted income approach. The Company calculated discounted cash flows of the Convertible Grant Agreement using a discount rate of 19.30% and adjusted for the probability of various repayment scenarios.

The following table reconciles the change in fair value of the Convertible Grant Agreement during the six months ended June 30, 2025 (in thousands):

5. Fair Value

The Company’s financial instruments that are measured at fair value on a recurring basis consist of money market funds and the Convertible Grant Agreement. The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy used to determine such fair values (in thousands):

The Company classifies its money market funds, which are valued based on quoted market prices in an active market with no valuation adjustment, as Level 1 assets within the fair value hierarchy. The Company’s Convertible Grant Agreement is classified as a Level 3 instrument under the fair value hierarchy as the fair values were determined based on significant inputs not observable in the market. See Note 4 for additional information on the Convertible Grant Agreement.

6. Asset Purchase and License Agreements

From time to time, the Company enters into asset purchase and license agreements with third parties. For a detailed description of the significant agreements with certain financial commitments to which the Company is a party, see Note 10 to the audited consolidated financial statements included in the Company’s Annual Report. As of June 30, 2025, the Company was a party to the following significant agreements pursuant to which payments were made during the three and six months ended June 30, 2024 and 2025:

Teva Asset Purchase Agreement

Effective October 4, 2021, the Company entered into an agreement with Teva Pharmaceutical Industries, Ltd to acquire patents, know-how and other rights to ALTO-203 and a specified related compound (the “Teva Acquired Compound”), and assumed all post-acquisition liabilities related thereto. In April 2024, the Company achieved a clinical milestone related to the initiation of its Phase 2 proof-of-concept (“POC”) clinical trial evaluating ALTO-203 resulting in a cash payment of $0.5 million which was recorded in research and development expenses during the three and six months ended June 30, 2024. Except for the foregoing $0.5 million milestone payment, no additional milestones or royalties were paid or accrued during the three and six months ended June 30, 2025 or 2024 related to this agreement. For adetailed description of the financial terms of the Teva asset purchase agreement, see Note 10 to the audited consolidated financial statements included in the Annual Report.

MedRx License Agreement

On September 25, 2023, the Company entered into a joint development and license agreement (the “MedRx Agreement”) with MedRx Co., Ltd. (“MedRx”), pursuant to which the Company obtained an exclusive, sublicensable, worldwide license, with the right to sublicense, under certain patent rights and know-how of MedRx relating to transdermal drug delivery to develop (excluding any pre-clinical development), manufacture, and commercialize transdermally delivered pharmaceutical products comprising MedRx’s transdermal patch technology and the Company’s ALTO-101 (the “MedRx Licensed Products”) for all therapeutic, prophylactic, and diagnostic uses. The Company granted MedRx an exclusive, sublicensable, worldwide license under certain patent rights and know-how relating to ALTO-101 owned or controlled by the Company, including certain patents and know how licensed to the Company pursuant to the Sanofi Agreement, solely to conduct pre-clinical development and manufacturing of the MedRx Licensed Products for the Company in accordance with the MedRx Agreement and a separate manufacturing and supply agreement to be entered into between the Company and MedRx. In April 2024, the Company achieved the desired pharmacokinetic profile for ALTO-101 in a Phase 1 trial resulting in a milestone payment to MedRx comprising $0.8 million, paid in cash, as well as 46,875 shares of the Company’s common stock. The Company recognized $1.5 million of expense related to this milestone, which was recorded in research and development expenses in the consolidated statements of operations and comprehensive loss during the three and six months ended June 30, 2024. Except for the $1.5 million milestone discussed above, no additional milestones or royalties were paid or accrued during thethree and six months ended June 30, 2025 or 2024 related to this agreement. For a detailed description of the financial terms of the MedRx Agreement, see Note 10 to the audited consolidated financial statements included in the Annual Report.

Chase Asset Purchase Agreement

On May 31, 2025 (the “Chase Closing Date”), the Company entered into an Asset Purchase Agreement (“Chase Agreement”) with Chase Therapeutics Corporation (“Chase”) to acquire all patent, know-how and other rights to ALTO-207, ALTO-208, and certain related assets (the “Acquired Compounds”).

On the Chase Closing Date, the Company made an initial payment of $1.8 million in cash and reimbursed Chase $1.2 million to offset certain expenses incurred by the Seller in connection with the Chase Agreement, which are recorded in Research and development in the consolidated statement of operations. The Company is obligated to pay Chase up to an aggregate of $71.5 million after the Chase Closing Date (the “Chase Milestone Payments”) upon the achievement of certain clinical, regulatory, and sales milestones related to the Acquired Compounds (the “Chase Milestone Events”). Of the potential Milestone Payments, $41.0 million in aggregate are tied to commercial success of the product candidates. Other than with respect to the first Chase Milestone Event, Chase may elect to receive the Chase Milestone Payments for each Chase Milestone Event either as cash or as restricted shares of the Company’s common stock, subject to an overall limitation of a maximum of 5,387,353 shares of common stock that may be issued pursuant to the Chase Agreement (representing 19.9% of the outstanding shares of the common stock as of the Chase Closing Date). No milestones or royalties were paid or accrued during the three and six months ended June 30, 2025 related to this agreement.

The number of shares of common stock issuable for a Chase Milestone Payment paid in restricted shares of common stock, will be determined by dividing the Chase Milestone Payment by the applicable Company Stock Price (as defined below), rounded down to the nearest share. The Company Stock Price is defined as thefive-day volume-weighted average price per share of common stock as reported by Bloomberg and calculated during regular trading hours over thefive consecutive trading day period ending on: (a) with respect to a Chase Milestone Payment pursuant to Chase’s election to receive a Chase Milestone Payment as common stock, the first trading day immediately following an Achievement Notice (as defined in the Chase Agreement); and (b) with respect a Deadline Milestone Payment (as defined below), the first trading day immediately following the applicable anniversary of the Closing Date.

The Company must use commercially reasonable efforts to develop, seek Regulatory Approval (as defined in the Chase Agreement) for, and commercialize products containing or comprising the Acquired Compounds in the United States. If the Company fails to achieve certain Chase Milestone Events by an agreed date, the Company must either pre-pay a portion of the relevant Chase Milestone Payment associated with that Chase Milestone Event, (a “Deadline Milestone Payment”), which pre-payment obligation may be paid in restricted shares of Common Stock, or transfer the related Acquired Compound back to Chase, in the Company’s sole discretion.

7. Stock-Based Plans

2024 Equity Incentive Plan

In January 2024, the Board adopted, and the Company’s stockholders approved, the 2024 Equity Incentive Plan (the “2024 Plan”), which became effective on the execution of the underwriting agreement related to the IPO. Under the 2024 Plan, the Company may grant incentive stock options to employees, including employees of any parent or subsidiary, and nonstatutory stock options, stock appreciation rights, RSAs, restricted stock unit awards, performance awards and other forms of stock awards to employees, directors, and consultants, including employees and consultants of the Company’s affiliates. The 2024 Plan is a successor to the 2019 Equity Incentive Plan, which was adopted by the Board of Directors in March 2019 (as amended, the “2019 Plan”). A total of 2,000,000 shares of common stock were approved to be initially reserved for issuance under the 2024 Plan. In addition, the number of shares of the Company’s common stock reserved for issuance under the 2024 Plan automatically increases on January 1 of each calendar year, starting on January 1, 2025 and continuing through and including January 1, 2034, in an amount equal to 5% of the total number of shares of the Company’s common stock outstanding on the last day of the calendar month before the date of each automatic increase, or a lesser number of shares determined by the Board. No future issuances were made under the 2019 Plan upon the effectiveness of the 2024 Plan.

As of June 30, 2025 and December 31, 2024, the total number of shares authorized to be issued under the 2024 Plan was 3,349,328 and 2,000,000, respectively. As of June 30, 2025 and December 31, 2024, there were 527,278 and 198 shares of common stock, respectively, reserved and available for issuance under the 2024 Plan.

2025 Inducement Plan

On February 6, 2025, the Board adopted the 2025 Inducement Plan (the “Inducement Plan”), pursuant to which it reserved 500,000 shares of common stock for issuance to individuals who were not previously employees of the Company, or who are returning to employment following a bona fide period of non-employment with the Company, as an inducement material to such persons entering into employment with the Company, in accordance with New York Stock Exchange Listed Company Manual Rule 303A.08. Under the Inducement Plan, the Company has the ability to issue non-statutory stock options, stock appreciation rights, restricted stock units (“RSUs”), restricted stock awards, and performance awards. As of June 30, 2025, no awards have been granted under the Inducement Plan.

Employee Stock Purchase Plan

As of June 30, 2025, the Company had not opened the Employee Stock Purchase Plan for enrollment, and therefore there were no purchases or share issuances during this period.

Stock Options

The options have a 10-year life and generally vest over a period offour years, with the first 25% of the award vesting afterone year and then monthly thereafter, subject to continuous service. Once the options are exercised, the shares are subject to transfer restrictions under the terms of the Company’s amended and restated certificate of incorporation.

The weighted-average grant date fair value of options granted during the three and six months ended June 30, 2025 for awards subject only to service-based vesting conditions were $1.91 and $2.91 per share, respectively. The weighted-average grant date fair value of options granted during the three and six months ended June 30, 2024 for awards subject only to service-based vesting conditions were $10.19 and $11.28 per share, respectively. Weighted-average grant date fair value assumptions were based on the following:

The table below summarizes activity related to stock options subject only to service-based vesting conditions (in thousands, except per share amounts):

As of June 30, 2025, there was approximately $17.2 million of unrecognized stock-based compensation expense related to these service-based unvested stock options which is expected to be recognized over a weighted-average period of 2.7 years.

Restricted Stock Units

The table below summ arizes activity related to RSUs subject only to service-based vesting conditions (in thousands, except per share amounts):

On March 1, 2024, the Company issued 53,864 RSUs under the 2024 Plan;50% of the shares of common stock underlying the RSUs vest after 18 months and the remainder vest after 24 months from the grant date. The RSUs are subject only to a service-based vesting condition. Such shares are not accounted for as outstanding until they vest. As of June 30, 2025, the total unrecognized compensation related to unvested RSUs granted was $0.3 million which is expected to be amortized on a straight-line basis over the weighted-average remaining vesting period of approximately 0.7 years.

Performance Option Awards

The Board granted options to purchase common stock to certain employees and consultants that vest upon the achievement of certain performance conditions (“Performance Awards”) such as the completion of a future financing event or upon the achievement of defined clinical milestones or outcomes. The Company didnot issue any Performance Awards during the three or six months ended June 30, 2025 and 2024.

During the six months ended June 30, 2024, clinical milestones were met which resulted in the vesting of 194,835 Performance Awards and the recognition of $0.9 million of stock-based compensation expense. During the six months ended June 30, 2025, there were 157,367 Performance Awards that were forfeited. As of June 30, 2025, there are 435,381 Performance Awards vested and outstanding, andno Performance Awards remain unvested. The Performance Awards have a contractual term often years. There isno unrecognized stock-based compensation expense related to Performance Awards.

Stock-based Compensation Expense

Non-cash stock-based compensation expense recognized in the accompanying condensed consolidated statements of operations and comprehensive loss for thethree and six months ended June 30, 2025 and 2024 was as follows (in thousands):

In July 2025, the Company’s Board of Directors approved a stock option repricing (see Note 13 for additional information).

8. Loss Per Share

Basic net loss per common share is computed by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. The Company’s unvested restricted common stock is not included in the determination of loss per share until the award vests. Diluted net loss per common share excludes the potential impact of the Company’s convertible preferred stock and warrants because their effect would be anti-dilutive due to the Company’s net loss. Since the Company had a net loss in each of the periods presented, basic and diluted net loss per common share are the same.

The following outstanding potentially dilutive common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive (in thousands):

9. Income Taxes

There isno provision for income taxes. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, including its net operating losses. Based on its history of operating losses, the Company believes that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for its net deferred tax assets as of June 30, 2025 and December 31, 2024.

On July 4, 2025, new legislation (commonly known as the One Big Beautiful Bill Act or OBBBA) was enacted into law in the U.S. The OBBBA includes significant provisions, such as the permanent extension of certain provisions that were originally enacted in the 2017 Tax Cuts and Jobs Act and were set to expire on December 31, 2025, modifications to certain international tax provisions and the restoration of tax treatment for certain business provisions, including 100% bonus depreciation for certain qualified property, domestic research and experimental cost expensing, and the business interest expense limitation. The new legislation has multiple effective dates, with certain provisions effective in 2025 and others implemented through 2027. The Company is currently evaluating the impact of the OBBBA to its condensed consolidated financial statements.

10. Convertible Preferred Stock and Stockholders’ Equity (Deficit)

Convertible Preferred Stock

Upon closing of the IPO in February 2024, all of the outstanding convertible preferred stock automatically converted into 13,664,261 shares of common stock. Subsequent to the closing of the IPO, there wereno shares of convertible preferred stock outstanding.

Preferred Stock

Series A Preferred Stock Warrants

In May 2021, in connection with the closing of the Series A Preferred Stock Agreement, the Company issued warrants to the lead Series A investor to purchase an aggregate of 465,917 shares of Series A Preferred Stock (“Series A Preferred Stock Warrants”) at a price of $4.6996 per share. By their terms, the Series A Preferred Stock Warrants expired in February 2024 in connection with the IPO. The Series A Preferred Stock Warrants were exercised and net settled for shares of the Company’s common stock, which resulted in the issuance of 72,631 shares of common stock. The Company remeasured the fair value of the Series A Preferred Stock Warrants immediately prior to their exercise, resulting in an insignificant change in fair value during the six months ended June 30, 2024. The resulting warrant liability was then extinguished upon the net exercise.

K2 Warrant

In December 2022, in connection with the closing of the Original Loan Agreement, the Company issued a warrant to the Lender to purchase a number of shares of the Company’s Series B convertible preferred stock, or at Lender’s election, next round stock (“K2 Warrant”). The number of shares of convertible preferred stock issuable upon exercise of the warrant was equal to (a) (i)0.0375, multiplied by (ii) the aggregate principal amount of term loans actually funded under the Original Loan Agreement, divided by (b) the warrant price then in effect. Following the conversion of all outstanding convertible preferred stock to common stock upon the completion of the IPO in February 2024, the K2 Warrant became a warrant to purchase up to an aggregate of 35,773 shares of the Company’s common stock at an exercise price of $10.49 per share (referred to in Note 4 as the Original Warrant). The K2 Warrant was remeasured to fair value immediately prior to the conversion to a common stock warrant, and a change in fair value of $0.2 million was recognized during the six months ended June 30, 2024. The Company determined that the K2 Warrant is equity-classified, and therefore the resulting warrant liability was reclassified to permanent equity, and is not subject to future remeasurement.

On January 13, 2025, in connection with the Amended Loan Agreement (see Note 4 for additional information), the K2 Warrant was amended and restated (referred to in Note 4 as the Amended and Restated Warrant) to reduce the exercise price from $10.49 per share to $3.71 per share (referred to in Note 4 as the Exercise Price). Further, in connection with the Amendment, the Company issued an additional warrant (referred to in Note 4 as the New Warrant and, together with the Amended and Restated Warrant, the Warrants) to purchase a number of shares of the Company’s common stock calculated as follows: (a) (i)0.025, multiplied by (ii) the aggregate principal amount of the term loans actually funded under the Amended Loan Agreement, divided by (b) the Exercise Price. The New Warrant expires on January 13, 2035. The New Warrant is classified as equity as it meets all the conditions under GAAP for equity classification, and is therefore not subject to ongoing remeasurement. The Company reassesses whether equity classification for the warrant is appropriate upon any changes to the warrants or capital structure, at each balance sheet date.

As of June 30, 2025 the New Warrant allowed for the purchase of 134,691 shares of the Company’s common stock. If the Company draws down on additional tranches of the Term Loan, the number of shares available for purchase by the Lender under the New Warrant would increase.

The Company is conditionally obligated to issue a fixed number of additional shares in connection with the New Warrant (“Additional Warrants”) in the potential amount of 370,400 shares upon the funding of additional amounts under the Term Loan with the same exercise price and contractual term. The contingent obligation to issue the Additional Warrants did not meet the derivative scope exception or equity classification criteria and were accounted for as a derivative liability. The contingently issuable Additional Warrants derivative liability had a de minimis value at the time of issuance and as of June 30, 2025. The Additional Warrants derivative liability will be remeasured each reporting period until settled or extinguished with subsequent changes in fair value recorded through other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The initial fair value of the Additional Warrants derivative liability was determined using a Black-Scholes option pricing model based on the same input assumptions above, with an additional assessment required for the probability that additional amounts under the Term Loan will be funded which would trigger the issuance of the Additional Warrants.

Common Stock and Authorized Shares

As of both June 30, 2025 and December 31, 2024, the Company had 500,000,000 authorized shares of common stock with a par value of $0.0001 per share, of which 27,072,129 and 26,986,560 shares, respectively, were issued and outstanding. On February 6, 2024, the Company amended its certificate of incorporation such that the total number of shares of common stock authorized to be issued was increased to 500,000,000, and the total number of shares of new preferred stock authorized to be issued was 10,000,000 with a par value per share of $0.0001. As of June 30, 2025, no shares of preferred stock were issued or outstanding.

As of June 30, 2025 and December 31, 2024, the Company had reserved common stock, on an as-if converted basis, for issuance as follows (in thousands):

11. Commitments and Contingencies

From time to time, the Company is subject to occasional lawsuits, investigations and claims arising out of the ordinary course of business. The Company had no significant pending or threatened litigation as of June 30, 2025.

On July 21, 2025, a purported stockholder of the Company filed a lawsuit against the Company, certain executive officers, and certain current and former directors in the United States District Court for the Northern District of California (Case No. 3:25-cv-06105). The complaint is a putative class action alleging violations of the Securities Act of 1933, as amended, or the Securities Act, related to the Company’s IPO in February 2025, and violations of the Exchange Act thereafter. The proposed class consists of purchasers or acquirers of the Company’s common stock pursuant or traceable to the Company’s IPO as well as purchasers or acquirers of the Company’s common stock between February 2, 2024 and October 22, 2024, both dates inclusive. The plaintiff seeks unspecified damages, as well as interest, fees, and costs. The complaint claims, among other things, that the Company’s offering documents and subsequent public disclosures contained materially false and misleading statements and omitted material facts about the prospects of ALTO-100. The Company believes these allegations lack merit, and the Company intends to move to dismiss. The Company has not recorded a liability related to this lawsuit because, at this time, the Company does not believe that an unfavorable outcome is either probable or estimable.

In the ordinary course of business, the Company enters into contracts that contain a variety of indemnifications with its employees, licensors, suppliers and service providers. Further, the Company indemnifies its directors and officers who are, or were, serving at the Company’s request in such capacities. The Company’s maximum exposure under these arrangements is unknown at June 30, 2025. The Company does not anticipate recognizing any significant losses relating to these arrangements.

12. Segments

As a single reportable segment entity, the Company’s segment performance measure is consolidated net loss. Asset information is not used by the Company’s President and Chief Executive Officer, its chief operating decision maker (“CODM”) to allocate resources. Certain significant segment expenses below loss from operations are presented in the Company’s consolidated statements of operations and are therefore not presented below. Additional disaggregated significant segment expenses on a functional basis, that are not separately presented on the Company’s condensed consolidated statements of operations, are presented below:

(a) Other research and development expenses primarily consists of license fees, facility charges, third party consultant costs, early research costs related to other product candidates, and other unallocated costs.

(b) General and administrative costs include professional fees, insurance, consultant fees and facility charges.

13. Subsequent Events

In July 2025, the Company’s Board of Directors approved a stock option repricing, which was effective at the close of market on July 3, 2025 (“Repricing Effective Date”). The repricing generally applied to the outstanding options held by then current employees and consultants that had an exercise price greater than $2.35. As of the Repricing Effective Date, the eligible options were immediately repriced such that the exercise price per share for such options was reduced to $2.35 (the closing price of the Company’s common stock on the New York Stock Exchange on the Repricing Effective Date), subject to certain retention requirements. The retention period is 12 months following the Repricing Effective Date and can be accelerated under certain conditions. If an eligible option is exercised prior to the end of the relevant retention period, the participant will be required to pay a premium exercise price equal to the original exercise price per share of such option. There were no changes to the number of shares underlying the eligible options or to the vesting schedules or expiration dates of the eligible options. There were 4,225,763 shares underlying the repriced options, which had then-current exercise prices ranging from $2.44 to $16.00 per share. An incremental $1.5 million of stock based compensation expense will be recognized over the greater of the 12-month retention period or the remaining vesting period of the outstanding options. Options held by non-employee members of the Board were not eligible for the repricing.