Spero Therapeutics, Inc. New Standards Disclosure

Recently Issued Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise noted, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its consolidated financial statements and disclosures.

In December 2025, the FASB issued ASU 2025-10, Accounting for Government Grants Received by Business Entities, to establish guidance on the recognition, measurement, and presentation of government grants received by business entities. The new guidance leverages the principles in the accounting framework for government assistance in IFRS, specifically IAS 20, Accounting for Government Grants and Disclosure of Government Assistance; makes certain targeted improvements; and modifies certain of the existing disclosure requirements in ASC 832, Government Assistance. The new guidance is effective for public business entities in annual periods beginning after December 15, 2028 (including interim periods within) and one year later for all other entities, with early adoption permitted in any period for which financial statements have not yet been issued. The guidance can be applied on a modified prospective basis, a modified retrospective basis, or a full retrospective basis. The Company is evaluating ASU 2025-10 to determine its impact on the Company's consolidated financial statements but does not expect there will be a material impact.

In September 2025, the FASB issued ASU 2025-07, Derivatives Scope Refinements and Scope Clarification for Share-Based Noncash Consideration from a Customer in a Revenue Contract. The new guidance will reduce the number of contracts (or embedded features within instruments) that are accounted for as derivatives under ASC 815, Derivatives and Hedging. The ASU adds a new scope exception to the derivatives guidance for underlying based on the operations or activities specific to one of the parties to the contract. The ASU also clarifies that share-based noncash consideration received from a customer as consideration for the transfer of goods or services in a revenue contract is subject to the revenue guidance and not the financial instruments guidance unless and until the company’s right to receive or retain the share-based noncash consideration is “unconditional,” as defined in the ASU. This ASU is effective for all entities for annual reporting periods beginning after December 15, 2025, and interim reporting periods within those annual reporting periods. The Company is evaluating ASU 2025-07 to determine its impact on the Company's consolidated financial statements but does not expect there will be a material impact.

In July 2025, the FASB issued ASU 2025-05, Measurement of Credit Losses for Accounts Receivable and Contract Assets. The ASU relates to estimating credit losses under CECL for current accounts receivable and current contract assets arising from revenue transactions accounted for under ASC 606, Revenue from Contracts with Customers, including those acquired in a transaction accounted for under ASC 805, Business Combinations. The ASU does not apply to other types of accounts receivable and loans. For all entities, the ASU provides a practical expedient to assume that current conditions as of the balance sheet date will persist through the reasonable and supportable forecast period for eligible assets. Entities will still be required to adjust historical data used in the estimation to reflect current conditions. In addition, entities other than public business entities can also make an accounting policy election to consider subsequent collections of balances received after the balance sheet date through a date selected by the entity. This policy election is available only if the entity elects the practical expedient. The date selected must be when or before financial statements are available to be issued. Under this accounting policy election, no credit loss would be recorded on balances that have been collected through subsequent receipts. Remaining uncollected amounts would be evaluated for credit losses using the practical expedient. This ASU is effective for all entities for annual reporting periods beginning after December 15, 2025, and interim reporting periods within those annual reporting periods. The Company is evaluating ASU 2025-05 to determine its impact on the Company's consolidated financial statements but does not expect there will be a material impact.

In November 2024, the FASB issued ASU 2024-03, “Disaggregation of Income Statement Expenses”, to provide disaggregated disclosures of specific expense categories underlying all relevant income statement expense line items on an annual and interim basis. The disclosure requirements will be applied on a prospective basis, with the option to apply them retrospectively. The effective date for the standard is for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. The Company is evaluating ASU 2024-03 to determine its impact on the Company's consolidated financial statements but does not expect there will be a material impact.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. ASU 2023-09 requires public companies to annually (i) disclose specific categories in the rate reconciliation and (ii) provide additional information for reconciling items that meet a quantitative threshold (if the effect of those reconciling items is equal to or greater than 5 percent of the amount computed by multiplying pretax income or loss by the applicable statutory income tax rate). ASU 2023-09 is effective for the annual reporting periods in fiscal years beginning after December 15, 2024. See Note 10, Income Taxes, for further information on the Company's adoption of ASU 2023-09 for its 2025 annual reporting.