Xilio Therapeutics, Inc.

We are a clinical-stage biotechnology company discovering and developing tumor-activated, or masked, immuno-oncology, or I-O, therapies with the goal of significantly improving outcomes for people living with cancer without the systemic side effects of current I-O treatments. We are leveraging our proprietary platform to advance a pipeline of novel, tumor-activated I-O molecules that are designed to optimize the therapeutic index by localizing anti-tumor activity within the tumor microenvironment, including masked antibodies, bispecifics, cytokines and immune cell engagers. Current I-O therapies have curative potential for patients with cancer. However, their potential is significantly curtailed by systemic toxicity that results from activity of the therapeutic molecule outside the tumor microenvironment. Our molecules are engineered to localize activity within the tumor microenvironment with minimal systemic effects, resulting in the potential to achieve enhanced anti-tumor activity and increasing the population of patients who may be eligible to receive our medicines. To date, we have presented data across our clinical-stage programs showing clinical validation for our tumor-activation platform. Our most advanced clinical-stage product candidates are vilastobart, a tumor-activated, Fc-enhanced anti-CTLA-4 monoclonal antibody, or mAb, and efarindodekin alfa (XTX301), a tumor-activated, engineered interleukin 12, or IL-12, therapy. We are currently advancing clinical development for vilastobart in combination with atezolizumab (Tecentriq®) in a Phase 2 clinical trial in patients with microsatellite stable metastatic colorectal cancer, or MSS mCRC, under a co-funded clinical trial collaboration with F. Hoffmann-La Roche Ltd, or Roche. In November 2025, we announced new data from the ongoing Phase 2 clinical trial at the Society for Immunotherapy of Cancer (SITC) 40 th Annual Meeting in patients with MSS mCRC without liver metastases and high plasma tumor mutational burden, or TMB, and we anticipate reporting additional data from the Phase 2 trial in the first half of 2026. Based on the promising clinical activity and safety profile demonstrated by vilastobart to date as a combination therapy, including in patients who had high plasma TMB, we are actively seeking a partner to develop vilastobart in combination with PD-(L)1 or PD1-VEGF in MSS mCRC and other tumor types. For efarindodekin alfa, in the third quarter of 2025, we initiated a Phase 2 trial in patients with advanced solid tumors and achieved a $17.5 million development milestone under our exclusive license agreement with Gilead Sciences, Inc., or Gilead. We have completed enrollment in the Phase 1A monotherapy dose escalation and Phase 1B monotherapy dose expansion portions of our ongoing Phase 1/2 clinical trial, and evaluation of patients is ongoing. In addition to our clinical-stage product candidates, we are leveraging our proprietary tumor-activation platform to advance multiple preclinical programs for XTX501, a bispecific PD-1/masked IL-2 and our masked T cell engager molecules, including wholly owned programs targeting the tumor-associated antigens for PSMA, CLDN18.2 and STEAP1 and an additional program under our collaboration, license and option agreement with AbbVie Group Holdings Limited, or AbbVie.

Liquidity and Going Concern Overview

To date, we have financed our operations primarily from proceeds raised through private placements of preferred units, convertible preferred stock, common stock and prefunded warrants; sales of common stock in our initial public offering, or IPO, and through “at-the-market” offerings; the sale of prefunded warrants and common stock warrants in a follow-on public offering; and upfront payments under our collaboration and license agreements with AbbVie and Gilead. 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. All of our programs are in early clinical or preclinical development. 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 public offering of prefunded warrants and accompanying common stock warrants and received net proceeds of $47.0 million after deducting underwriting discounts and commissions and offering expenses payable by us. In connection with the offering, we issued prefunded warrants to purchase 66,676,000 shares of common stock, accompanied by Series A warrants to purchase 66,676,000 shares of common stock (or, in certain circumstances, prefunded warrants), Series B warrants to purchase 66,676,000 shares of common stock (or, in certain circumstances, prefunded warrants) and Series C warrants to purchase 66,676,000 shares of common stock (or, in certain circumstances, prefunded warrants). If all of the Series B warrants and Series C warrants are exercised in cash at their initial exercise price of $0.75 per warrant, we will receive up to $100.0 million of additional gross proceeds by the second half of 2026. For more information, refer to Note 8 to our condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q.

Since inception, we have incurred significant operating losses, including net losses of $45.4 million and $45.1 million for the nine months ended September 30, 2025 and 2024, respectively, and a net loss of $58.2 million for the year ended December 31, 2024. As of September 30, 2025, we had an accumulated deficit of $429.1 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 September 30, 2025, we had cash and cash equivalents of $103.8 million. In the fourth quarter of 2025, we received a $17.5 million development milestone under our license agreement with Gilead. Based on our current operating plans, we anticipate that our existing cash and cash equivalents as of September 30, 2025, together with the $17.5 million development milestone received under our license agreement with Gilead, will be sufficient to enable us to fund our operating expenses and capital expenditure requirements into the first quarter of 2027. However, 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. In addition, 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, tumor-activated 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. These conditions raise substantial doubt about our ability to continue as a going concern. In order to fund our operations, we will need to raise additional capital, which could be obtained through the cash exercise of the Series B warrants and Series C warrants issued in connection with our June 2025 follow-on public offering, the receipt of milestone payments, option-related fees or other contingent payments under our existing agreements with Gilead and AbbVie, additional public or private equity offerings, debt financings, additional collaborations, partnerships or licensing arrangements or other sources. However, there can be no assurance that we will receive additional proceeds from the exercise of the common stock warrants or from contingent payments under our existing agreements with Gilead or AbbVie or that we will be able to complete any such transaction on acceptable terms or otherwise. If we are not able to secure sufficient additional capital when needed, we may need to implement additional cost reduction strategies, which could include delaying, limiting, further reducing or eliminating both internal and external costs related to our operations and research and development programs.

For more information regarding our liquidity and going concern, refer to “—Liquidity and Capital Resources—Capital Requirements and Going Concern” below and Note 1 to our condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q. For more information regarding the terms of the warrants we issued in our June 2025 follow-on public offering, refer to Note 8 to our condensed consolidated financial statements included elsewhere in this Quarterly Report on Form 10-Q.