Significant Accounting Policies

12 Months Ended

Dec. 31, 2025

Accounting Policies [Abstract]

Significant Accounting Policies

Note 2—Significant Accounting Policies

Basis of Presentation

The Company’s financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented.

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of Taysha and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.

Smaller Reporting Company

We are a smaller reporting company as defined in the Exchange Act. We may take advantage of certain of the scaled disclosures available to smaller reporting companies and will be able to take advantage of these scaled disclosures for so long as (i) the value of our voting and non-voting common stock held by non-affiliates is less than $250.0 million measured on the last business day of our most recently completed second fiscal quarter or (ii) our annual revenue is less than $100.0 million during the most recently completed fiscal year and our the value of voting and non-voting common stock held by non-affiliates is less than $700.0 million measured on the last business day of our most recently completed second fiscal quarter.

As a smaller reporting company, we may continue to rely on exemptions from certain disclosure requirements that are available to smaller reporting companies. Specifically, as a smaller reporting company, we may choose to present only the two most recent fiscal years of audited financial statements in our Annual Report on Form 10-K and, similar to emerging growth companies, smaller reporting companies have reduced disclosure obligations regarding executive compensation.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The most significant estimates and assumptions in the Company’s financial statements relate to estimating manufacturing accruals and accrued or prepaid research and development expenses, the measurement of impairment of long-lived assets, and the valuation of the Trinity Term Loans that are carried at fair value. 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. Actual results may differ materially from these estimates. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected.

Risks and Uncertainties

The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, development by the Company or its competitors of technological innovations, risks of failure of clinical studies, dependence on key personnel, protection of proprietary technology, compliance with government regulations, and ability to transition from preclinical manufacturing to commercial production of products.

The Company’s product candidates require approvals from the FDA and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.

Segments

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as a single operating segment, the gene therapy segment, which is the business of developing AAV-based gene therapies for the treatment of rare monogenic diseases of the central nervous system. See Note 15 for additional information.

As of December 31, 2025 and 2024, the Company did not have any significant long-lived assets located outside of the United States.

Revenue Recognition

The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers, (“ASC 606”). Revenues consist of activities in connection with the Astellas Transactions, including the exclusive option to license intellectual property and the performance of research and development activities. See Note 7 for additional information.

The Company evaluates the agreement to determine if the other party is a customer, and then determines the units of account within the agreement to determine which promised goods or services are distinct. In order for a promised good or service to be considered “distinct” under ASC 606, the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (i.e., the good or service is capable of being distinct), and the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (i.e., the promise to transfer the good or service is distinct within the context of the contract).

For any units of account that fall within the scope of ASC 606, where the other party is a customer, the Company (i) evaluates the separate performance obligation(s) under each contract, (ii) determines the transaction price, (iii) allocates the transaction price to each performance obligation considering the estimated standalone selling prices of the services and (iv) recognizes revenue when, or as, the Company satisfies the performance obligation(s).

At the inception of an arrangement that includes options for a customer to purchase additional services or products at agreed upon prices in the future, the Company evaluates whether each option provides a material right. An option that provides a material right will be accounted for as a separate performance obligation.

As part of the accounting for arrangements under ASC 606, the Company must use significant judgment to determine the performance obligations, the transaction price, and the standalone selling price (“SSP”) for each performance obligation identified in the contract for the allocation of the transaction price. The SSP is the price at which an entity would sell a promised good or service separately to a customer. Management estimates the SSP of each of the identified performance obligations, maximizing the use of observable inputs. Because the Company has not sold the same goods or services in its contracts separately to any customers on a standalone basis, the Company utilizes similar observable transactions in the marketplace or estimates the SSP of each performance obligation in its customer arrangements at contract inception based on either (1) its estimate of costs to be incurred to fulfill its obligations associated with the performance obligation, plus a reasonable margin, or (2) an estimate that reflects the discount that the customer would obtain when exercising its option adjusted for (i) any discount that the customer could receive without exercising the option and (ii) the likelihood that the option will be exercised. The Company allocates the transaction price to each performance obligation in proportion to its SSP.

A performance obligation is satisfied and revenue is recognized when “control” of the promised good or service is transferred, either over time or at a point in time, to the customer. A customer obtains control of a good or service if it has the ability to (1) direct its use and (2) obtain substantially all of the remaining benefits from it.

Amounts received prior to satisfying the revenue recognition criteria listed above are recorded as deferred revenue in the accompanying consolidated balance sheets. Amounts expected to be recognized as revenue within 12 months of the balance sheet date are classified as current deferred revenue, including the amounts allocated to material rights which are subject to customer exercise at any point. Amounts not expected to be recognized as revenue within the following 12 months of the balance sheet date are classified as deferred revenue, net of current portion. The Company does not incur commission or other costs to fulfill customer contracts and as such, no capitalized contract costs are recorded on the consolidated balance sheets.

Cash and Cash Equivalents

Cash and cash equivalents consist of funds held in a standard checking account, a standard savings account and a money market fund. The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of December 31, 2025 and 2024, the Company had $317.1 million and $138.3 million in cash equivalents, respectively.

Restricted Cash

Restricted cash consists of cash that the Company has placed in an escrow account which is pledged as collateral under certain lease agreements and letters of credit.

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash and cash equivalents. Periodically, the Company may maintain deposits in financial institutions in excess of government insured limits. Management believes that the Company is not exposed to significant credit risk as the Company’s deposits are held at financial institutions that management continues to believe to be of high credit quality. The Company has not experienced any losses on these deposits.

Fair Value of Financial Instruments

The Company’s financial assets and liabilities are accounted for in accordance with ASC 820, Fair Value Measurements which defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value hierarchy requires an entity to maximize the use of observable inputs when measuring fair value and classifies those inputs into three levels:

Level 1—Observable inputs, such as quoted prices in active markets for identical assets or liabilities.

Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life.

Level 3—Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

The carrying values reported in the Company’s consolidated balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities are reasonable estimates of their fair values due to the short-term nature of these items.

Fair Value Option

The fair value option provides an election that allows a company to irrevocably elect to record certain financial assets and liabilities at fair value on an instrument-by-instrument basis at initial recognition. The Company has elected to apply the fair value option to the Trinity Term Loans.

The term loans accounted for under the fair value option election are each a debt host financial instrument containing embedded features that would otherwise be required to be bifurcated from the debt-host and recognized as separate derivative liabilities subject to initial and subsequent periodic estimated fair value measurements in accordance with GAAP. Notwithstanding, when the fair value option election is applied to financial liabilities, bifurcation of an embedded derivative is not required, and the financial liability is initially measured at its issue-date estimated fair value and then subsequently remeasured at estimated fair value on a recurring basis as of each reporting period date.

The portion of the change in fair value attributed to a change in the instrument-specific credit risk is recognized as a component of other comprehensive income or loss if material and the remaining amount of the fair value adjustment is recognized as a component of other income (expense) in the consolidated statements of operations.

Deferred Offering Costs

The Company capitalizes costs directly associated with equity financings until such financings are consummated, at which time such costs are recorded in additional paid-in capital against the gross proceeds of the equity financings. Costs associated with the shelf registration statement on Form S-3, filed with the SEC on December 13, 2024 were capitalized and reclassified to additional paid-in capital on a pro rata basis when the Company completed offerings under the shelf registration. On November 2, 2025, the Company entered into a new shelf registration on Form S-3. The Company capitalized costs associated with the shelf registration statement on Form S-3 filed with

the SEC on November 2, 2025 and reclassifies to additional paid-in capital on a pro rata basis as the Company completes offering under the shelf registration. At the end of the three-year term of the shelf registration, the remaining deferred offering costs, if any, will be charged to operations.

Property, Plant and Equipment, net

Property, plant and equipment, net are stated at cost less accumulated depreciation and consist of computer equipment, laboratory equipment and leasehold improvements. Depreciation expense is recognized using the straight-line method over its estimated useful life of three to seven years.

Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred.

Leases

The Company accounts for its lease agreements in accordance with ASC 842, Leases. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable.

Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. To estimate its incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating.

The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of use not included in the original lease and when lease payments increase commensurate with the standalone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease.

The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets.

Impairment of Long-Lived Assets

The Company evaluates its long-lived assets, which consist of property, plant and equipment as well as right-of-use assets, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. The Company performed an undiscounted cash flow analysis over the long-lived assets associated with the manufacturing facility and determined that the carrying value of the asset group is not recoverable. During the year ended December 31, 2024, the Company recorded a non-cash impairment charge of $4.8 million in connection with the North Carolina manufacturing facility. The impairment charge was estimated using a discounted cash flow model. Significant assumptions used to determine this non-recurring fair value measurement include the time to sublease the facility, the amount of sublease income expected to be generated over the remaining lease term, and the discount rate used to measure the present value of the net cash flows associated with this asset group. See Note 4 for additional information.

Debt Issuance Costs

Debt issuance costs related to the Trinity Term Loans are expensed as incurred due to the election of the fair value option.

Research and Development

The Company has entered into research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and are reflected

on the consolidated balance sheets as prepaid or accrued expenses. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs.

Research and development costs primarily consist of payroll, stock-based compensation, certain manufacturing costs, laboratory costs and other supplies, and the cost to acquire third-party licenses. Costs incurred in obtaining technology licenses through asset acquisitions are charged to research and development expense if the licensed technology has not reached technological feasibility and has no alternative future use. Payments of such upfront license fees and subsequent development milestones are included as investing cash outflows in the consolidated statements of cash flows.

Stock-Based Compensation

The Company accounts for all stock-based payments to employees and non-employees, including grants of stock options, restricted stock awards (“RSAs”), and restricted stock units (“RSUs”), based on their respective grant date fair values. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, which is affected principally by the estimated fair value of shares of the Company’s common stock and requires management to make a number of other assumptions, including the expected life of the option, the volatility of the underlying shares, the risk-free interest rate and expected dividends. Expected volatility is based on the historical share volatility of a set of comparable publicly traded companies over a period of time equal to the expected term of the options. Due to the lack of historical exercise history, the expected term of the Company’s stock options is determined using the “simplified” method. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

The RSAs and RSUs are valued based on the fair value of the Company’s common stock on the date of grant. The Company expenses stock-based compensation related to stock options, RSAs and RSUs which contain only service-based vesting conditions over the requisite service period using the straight-line method. For awards which contain only performance conditions, the Company recognizes expense based on the fair value of the awards in the period in which the achievement of the related performance conditions is estimated to be probable. For awards with both performance and service conditions, the Company recognizes expense based on the fair value of the performance awards over the estimated service period using the accelerated attribution method to the extent the achievement of the related performance criteria is estimated to be probable. At each reporting date, the Company evaluates whether any performance conditions related to a performance-based award have changed. The effect of any change in performance conditions is recognized as a cumulative catch-up adjustment in the period such change occurs. Stock-based compensation costs are initially recorded in research and development expense or general and administrative expense in the consolidated statements of operations in a manner consistent with the classification of the respective employee’s payroll costs. Forfeitures are recorded as they occur.

Warrants

The Company accounts for warrants as either equity-classified or liability-classified instruments based on an assessment of the warrant’s specific terms and applicable authoritative guidance in FASB ASC 480, Distinguishing Liabilities from Equity (“ASC 480”) and ASC 815, Derivatives and Hedging (“ASC 815”). The assessment considers whether the warrants are freestanding financial instruments pursuant to ASC 480, meet the definition of a liability pursuant to ASC 480, and whether the warrants meet all of the requirements for equity classification under ASC 815, including whether the warrants are indexed to the Company’s own common shares and whether the warrant holders could potentially require “net cash settlement” in a circumstance outside of the Company’s control, among other conditions for equity classification. This assessment, which requires the use of professional judgment, is conducted at the time of warrant issuance and as of each subsequent reporting period while the warrants are outstanding.

For issued or modified warrants that meet all of the criteria for equity classification, the warrants are required to be recorded as a component of additional paid-in capital at the time of issuance, or when the conditions for equity classification are met, and are not remeasured. For issued or modified warrants that do not meet all the criteria for equity classification, the warrants are required to be recorded at their initial fair value on the date of issuance, and each balance sheet date thereafter. Liability-classified warrants are recorded at their fair value, and the Company adjusts such warrants to fair value at each reporting period. This liability is subject to remeasurement at each balance sheet date until the warrants are exercised or expire, and any change in fair value is recognized in the Company’s consolidated statements of operations.

Income Taxes

Income taxes are recorded in accordance with ASC 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. 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, and net operating loss (“NOL”) carryforwards and research and development tax credit (“R&D Credit”) carryforwards. 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 recorded a full valuation allowance to reduce its net deferred income tax assets to zero. In the event the Company were to determine that it would be able to realize some or all of its deferred income tax assets in the future, an adjustment to the deferred income tax asset valuation allowance would increase income in the period such determination was made.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit would more likely than not be realized assuming examination by the taxing authority. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. During the year ended December 31, 2025 the Company recorded increases in the amount of gross unrecognized tax benefits of $2.2 million. During the year ended December 31, 2024, the Company recorded increases in the amount of unrecognized tax benefits of $1.8 million. The Company also reduced its uncertain tax positions during 2023 by $7.8 million related to prior year positions largely as a result of the Section 382 ownership shift analysis performed during 2023 (see Note 12). The unrecognized tax benefits, if recognized, would not affect the effective income tax rate due to the valuation allowance that currently offsets deferred tax assets. The Company does not expect the unrecognized tax benefits to change significantly over the next 12 months. The Company would recognize any corresponding interest and penalties associated with its income tax positions in income tax expense. There was no income tax interest or penalties incurred for the years ended December 31, 2025 and 2024.

Comprehensive Loss

Comprehensive income includes charges and credits to shareholders' equity that are not the result of transactions with shareholders. Our total comprehensive loss consists of net income and changes in fair value attributed to instrument-specific credit risk from the 2025 Trinity Term Loans (as defined below). The items of comprehensive loss, with the exception of net loss, are included in accumulated other comprehensive loss in the consolidated balance sheets and statements of shareholders' equity.

Recently Adopted Accounting Pronouncements

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which focuses on the rate reconciliation and income taxes paid. ASU No. 2023-09 requires a public business entity (“PBE”) to disclose, on an annual basis, a tabular rate reconciliation using both percentages and currency amounts, broken out into specified categories with certain reconciling items further broken out by nature and jurisdiction to the extent those items exceed a specified threshold. In addition, all entities are required to disclose income taxes paid, net of refunds received disaggregated by federal, state/local, and foreign and by jurisdiction if the amount is at least 5% of total income tax payments, net of refunds received. For PBEs, the new standard is effective for annual periods beginning after December 15, 2024, with early adoption permitted. An entity may apply the amendments in this ASU prospectively by providing the revised disclosures for the period ending December 31, 2025 and continuing to provide the pre-ASU disclosures for the prior periods, or may apply the amendments retrospectively by providing the revised disclosures for all period presented. As of December 31, 2025, the Company adopted this new ASU retrospectively with all the revised disclosures as required by this ASU in Note 12.

Recently Issued Accounting Pronouncements

In November 2024, the FASB issued ASU No. 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures, to improve expense disclosure requirements under ASC 220, Income Statement - Reporting Comprehensive Income, through enhancing disclosures about significant segment expenses. The guidance requires entities to provide additional disclosure about specific expenses by requiring entities to disaggregate, in a tabular presentation, each relevant expense caption on the face of the income statement that includes any of the following natural expenses (1) purchases of inventory, (2) employees compensation, (3) depreciation, (4) intangible asset amortization, and (5) depreciation, depletion and amortization recognized as part of oil - and gas - producing activities or other types of depletion expenses. The tabular disclosure would also include certain other expenses, when applicable. The ASU also enhances interim segment reporting requirements by aligning interim disclosures with information that must be disclosed annually in accordance with ASC 220. The guidance is effective for annual periods beginning after December 15, 2026, and interim periods beginning after December 15, 2027, applied either prospectively or retrospectively with early adoption permitted. The Company is still evaluating the impact this ASU will have on its disclosures.