Xilio Therapeutics, Inc.

We are a clinical-stage biotechnology company discovering and developing masked immuno-oncology, or I-O, therapies with the goal of significantly improving outcomes for people living with cancer. Leveraging our clinically-validated masking technology and capabilities, we are developing I-O therapies designed to selectively activate within the tumor microenvironment to achieve durable efficacy without the severe side effects associated with systemically active I-O agents. Our integrated biology and protein engineering approach enables us to design and develop highly potent, masked biologics that are activated, or unmasked, by tumor-specific proteases within the tumor microenvironment. We are currently advancing multiple programs in preclinical and clinical development, including masked multi-specifics, and our clinically-validated masking technology has enabled us to establish top-tier strategic partnerships, including with AbbVie Group Holdings Limited, or AbbVie, and Gilead Sciences, Inc., or Gilead.

Recent Events

On March 12, 2026, we filed a certificate of amendment to our restated certificate of incorporation to effect 1-for-14 reverse stock split of our issued and outstanding shares of common stock, without any change to par value, which became effective at 5:00 P.M. Eastern Time on March 13, 2026. Unless otherwise indicated, all share amounts and per share amounts of our common stock have been adjusted retroactively in this Annual Report on Form 10-K to give effect to the reverse stock split for all periods presented.

In February 2026, we received net proceeds of approximately $37.3 million, after deducting underwriting discounts and commissions and estimated offering expenses payable by us, upon the closing of a follow-on offering of prefunded warrants. In connection with the offering, we issued prefunded warrants to purchase 5,341,404 shares of our common stock. Each prefunded warrant is exercisable for one share of our common stock. The purchase price of each warrant was $7.4886. Each prefunded warrant has an exercise price of $0.0014 per share and will be exercisable from the date of issuance until fully exercised, subject to a beneficial ownership limitation for each holder.

Liquidity Overview

To date, we have financed our operations primarily from proceeds raised through private placements of equity securities; sales of common stock in our initial public offering, or IPO, and through “at-the-market” offerings; the sale of prefunded warrants in our June 2025 and February 2026 follow-on offerings; the exercise of certain common stock warrants issued in connection with our June 2025 follow-on offering; development event payments under our co-funded clinical trial collaboration with F. Hoffmann-La Roche Ltd., or Roche; and upfront and milestone payments under our collaboration and license agreements with AbbVie and Gilead. All of our programs are in early clinical or preclinical development. As a result, we have not generated any revenue from product sales and do not expect to generate any revenue from product sales for at least the next several years, if at all. Our ability to generate product revenue sufficient to achieve profitability will depend heavily on the successful development and eventual commercialization of one or more of our product candidates, if approved. Because of the numerous risks and uncertainties associated with product development, we are unable to predict the timing or amount of increased expenses or when or if we will be able to achieve profitability. Even if we are able to generate revenue from product sales, we may not become profitable.

In June 2025, we closed a follow-on offering of prefunded warrants and accompanying common stock warrants and received net proceeds of $47.0 million. In connection with the offering, we issued prefunded warrants to purchase 4,762,533 shares of common stock, accompanied by Series A warrants to purchase 4,762,533 shares of common stock (or, in certain circumstances, prefunded warrants), Series B warrants to purchase 4,762,533 shares of common stock (or, in certain circumstances, prefunded warrants) and Series C warrants to purchase 4,762,533 shares of common stock (or, in certain circumstances, prefunded warrants). Through

December 31, 2025, 3,443,388 of the Series B warrants were exercised for 1,008,415 shares of common stock and 2,434,973 prefunded warrants in lieu of shares of common stock. We received approximately $35.8 million in total gross proceeds from the exercise of the Series B warrants, before deducting underwriting discounts and commissions and any offering expenses. An aggregate of 3,443,388 Series C warrants, which are exercisable between June 1, 2026 and December 2, 2026, remain outstanding and 1,319,145 Series C warrants expired on December 31, 2025 according to their terms in connection with the expiration of unexercised Series B warrants. If all of the outstanding Series C warrants are exercised for cash at their current exercise price of $10.50 per warrant, we would receive up to $36.2 million in additional total gross proceeds in the second half of 2026, before deducting underwriting discounts and commissions and any offering expenses.

Since inception, we have incurred significant operating losses, including net losses of $35.0 million and $58.2 million for years ended December 31, 2025 and 2024, respectively. As of December 31, 2025, we had an accumulated deficit of $418.8 million. We expect to continue to incur significant expenses and operating losses for the foreseeable future, particularly to the extent we:

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continue to advance our current research programs and conduct additional research programs;

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advance our current product candidates and any future product candidates we may develop into preclinical and clinical development;

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seek marketing approvals for product candidates that successfully complete clinical trials, if any;

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obtain, expand, maintain, defend and enforce our intellectual property;

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continue to discover, validate and develop additional product candidates;

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continue to manufacture increasing quantities of our current or future product candidates for use in preclinical studies, clinical trials and for any potential commercialization;

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acquire or in-license other product candidates, technologies or intellectual property;

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hire additional personnel to support current or future programs;

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establish a commercial and distribution infrastructure to commercialize products for which we may obtain marketing approval, if any; and

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incur additional costs associated with current and future research, development and commercialization efforts and operations as a public company.

As a result, we will need substantial additional capital to support our continuing operations and pursue our strategy. As of December 31, 2025, we had cash and cash equivalents of $137.5 million. In the first quarter of 2026, we received net proceeds of approximately $37.3 million, after deducting underwriting discounts and commissions and estimated offering expenses payable by us, upon the closing of a follow-on offering of prefunded warrants and a $5.0 million development milestone related to the collaboration agreement with AbbVie. Based on our current operating plans, we anticipate that our existing cash and cash equivalents will be sufficient to enable us to fund our operating expenses and capital expenditure requirements through the end of 2027. This estimate excludes any potential future milestone payments, option-related fees or other contingent payments under our existing collaboration and partnership agreements with AbbVie and Gilead and excludes the potential receipt of up to $36.2 million in additional gross proceeds in the second half of 2026 if all outstanding Series C warrants are exercised at their current exercise price.

In addition, we have based our estimates on assumptions that may prove to be wrong, and we could exhaust our available capital resources sooner than we anticipate. We expect our operating losses and negative operating cash flows to continue for the foreseeable future as we continue to advance our pipeline of novel, masked I-O molecules through preclinical and clinical development, maintain the infrastructure necessary to support these activities and continue to incur costs associated with operating as a public company.