Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 10-K ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2025 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from ________ to ________. Commission file number: 001-40925 XILIO THERAPEUTICS, INC. (Exact name of registrant as specified in its charter) Delaware 85-1623397 ...

Financial Estimates - As of December 31, 2025, Xilio Therapeutics, Inc. estimates cash and cash equivalents of approximately $137.5 million[4] - The cash balance estimate is based on preliminary, unaudited information and management estimates for the fiscal year ended December 31, 2025[5] Leadership Changes - The company announced the appointment of Sara M. Bonstein as chair of the Board, succeeding Paul Clancy who retired on January 6, 2026[7]

Core Insights - Xilio Therapeutics is advancing its pipeline of masked immuno-oncology therapies, including XTX501, a bispecific PD-1 / masked IL-2, with plans for IND submission in mid-2026 and Phase 1 initiation in the second half of 2026 [1][7] - The company is also developing a first-in-class multi-specific masked T cell engager targeting PSMA and STEAP1, with a development candidate expected to be nominated in Q2 2026 [3][11] - Xilio has extended its cash runway through the end of 2027, with cash and cash equivalents reported at $137.5 million as of December 31, 2025 [13][12] Pipeline Progress and Business Updates - XTX501 is designed to selectively stimulate PD-1 positive, antigen-experienced T cells, demonstrating robust monotherapy activity in preclinical studies [4] - The company is leveraging its proprietary masking technology to advance multiple masked T cell engager programs, including a collaboration with AbbVie [5][11] - Xilio plans to present new preclinical data for its CLDN18.2 program at the AACR Annual Meeting in April 2026 [11] Financial Performance - Collaboration and license revenue increased significantly to $13.7 million for Q4 2025, compared to $1.7 million in Q4 2024, and $43.8 million for the full year 2025, up from $6.3 million in 2024 [12][17] - Research and development expenses rose to $18.1 million for Q4 2025, compared to $8.8 million in Q4 2024, driven by IND-enabling studies and clinical development activities [12][17] - The net income for Q4 2025 was $10.4 million, a significant improvement from a net loss of $13.1 million in Q4 2024, while the net loss for the full year decreased to $35.0 million from $58.2 million [17][12]

Core Insights - Xilio Therapeutics, Inc. is set to present a poster at the American Association for Cancer Research (AACR) Annual Meeting, focusing on their masked immuno-oncology therapy, XTX601, which targets Claudin 18.2 [1] Company Overview - Xilio Therapeutics is a clinical-stage biotechnology company dedicated to developing masked immuno-oncology therapies aimed at improving cancer treatment outcomes while minimizing systemic side effects associated with current therapies [2]

Core Viewpoint - Xilio Therapeutics, Inc. will implement a 1-for-14 reverse stock split to increase the per-share market price of its common stock and regain compliance with Nasdaq listing requirements [2][4]. Group 1: Reverse Stock Split Details - The reverse stock split will be effective at 5:00 p.m. Eastern Time on March 13, 2026, and trading on a split-adjusted basis will begin on March 16, 2026 [1][3]. - The number of outstanding shares will decrease from approximately 73.5 million to about 5.2 million shares [4]. - No fractional shares will be issued; stockholders entitled to a fractional share will receive a cash payment instead [5]. Group 2: Stockholder and Market Impact - The reverse stock split was approved by stockholders at a Special Meeting on February 23, 2026, with the final ratio determined by the Board of Directors [2]. - The split aims to help the company meet the minimum bid price requirement for continued listing on the Nasdaq Capital Market [2]. - All outstanding warrants and securities will be adjusted accordingly, and proportionate adjustments will be made to equity incentive plans [4][6]. Group 3: Company Overview - Xilio Therapeutics is a clinical-stage biotechnology company focused on developing masked immuno-oncology therapies to improve cancer treatment outcomes while minimizing systemic side effects [7].

Core Viewpoint - Xilio Therapeutics, Inc. is participating in a fireside chat at the Leerink Partners Global Healthcare Conference on March 9, 2026, to discuss its advancements in masked immuno-oncology therapies for cancer patients [1]. Company Overview - Xilio Therapeutics is a clinical-stage biotechnology company focused on discovering and developing masked immuno-oncology therapies aimed at improving cancer treatment outcomes while minimizing systemic side effects associated with current therapies [3]. - The company utilizes proprietary masking technology to create a pipeline of novel masked immuno-oncology molecules, which are designed to enhance therapeutic efficacy by targeting anti-tumor activity specifically within the tumor microenvironment [3]. Event Information - A live webcast of the fireside chat will be available under the "Events & Presentations" section on the Xilio Therapeutics website, with a replay accessible for 30 days post-presentation [2].

Core Viewpoint - Xilio Therapeutics, Inc. has announced a pre-funded warrant offering to raise approximately $40 million to support the development of its immuno-oncology therapies and for general corporate purposes [1][2]. Group 1: Offering Details - The offering consists of 74,780,300 pre-funded warrants priced at $0.5349 each, with an exercise price of $0.0001 per share [1]. - The pre-funded warrants are immediately exercisable and will remain valid until fully exercised [1]. - The offering is expected to close on or about February 13, 2026, pending customary closing conditions [1]. Group 2: Financial Aspects - Gross proceeds from the offering are anticipated to be around $40 million before deducting underwriting discounts and commissions [2]. - The proceeds will be utilized to advance product candidates and for working capital and other corporate needs [2]. Group 3: Investor Participation - The financing was led by Coastlands Capital, with participation from Gilead Sciences, Inc., OrbiMed, Perceptive Advisors, and other institutional investors [3]. - Leerink Partners is serving as the sole bookrunner for the offering [3]. Group 4: Company Overview - Xilio Therapeutics is focused on developing masked immuno-oncology therapies aimed at improving cancer treatment outcomes while minimizing systemic side effects [6]. - The company employs proprietary masking technology to create novel I-O molecules that target anti-tumor activity within the tumor microenvironment [6].

Core Insights - Xilio Therapeutics, Inc. has successfully raised $35.8 million through Series B warrant exercises, extending its cash runway into the second quarter of 2027 [1][4][8] - The company achieved a development milestone for its masked antibody-based program under the collaboration with AbbVie and nominated a development candidate for its masked T cell engager program targeting CLDN18.2 [1][6] - Sara Bonstein has been appointed as the chair of the board of directors, succeeding Paul Clancy [1][6][3] Financial Updates - As of December 31, 2025, Xilio reported cash and cash equivalents of $137.5 million, which includes the recent $35.8 million raised [7][8] - The funds are expected to support the company's operating expenses and capital expenditures through the second quarter of 2027 [8] Corporate Developments - The appointment of Sara Bonstein as chair of the board is seen as a strategic move, given her extensive experience in finance and biotechnology [6][3] - The company has made significant progress in demonstrating the validation of its masking technology through partnerships with Gilead and AbbVie [3][6] Anticipated Milestones - Xilio plans to submit an investigational new drug (IND) application for XTX501 in mid-2026 and report initial Phase 1 data in the second half of 2027 [12] - The company aims to advance at least two masked T cell engager programs into IND-enabling studies and submit IND applications for those programs in 2027 [12]

Core Insights - Xilio Therapeutics reported a quarterly loss of $0.03 per share, which aligns with the Zacks Consensus Estimate, showing improvement from a loss of $0.22 per share a year ago [1] - The company posted revenues of $19.07 million for the quarter ended September 2025, missing the Zacks Consensus Estimate by 28.51%, compared to revenues of $2.26 million in the same quarter last year [2] - Xilio Therapeutics shares have declined approximately 19% year-to-date, contrasting with a 16.5% gain in the S&P 500 [3] Financial Performance - The company has not surpassed consensus revenue estimates over the last four quarters [2] - The current consensus EPS estimate for the upcoming quarter is -$0.12 on revenues of $7.96 million, and for the current fiscal year, it is -$0.45 on revenues of $45.65 million [7] Market Outlook - The earnings outlook and management's commentary during the earnings call will be crucial for the stock's immediate price movement [3][4] - The Zacks Rank for Xilio Therapeutics is currently 3 (Hold), indicating expected performance in line with the market in the near future [6] Industry Context - The Medical - Biomedical and Genetics industry is currently in the top 35% of Zacks industries, suggesting a favorable outlook compared to the bottom 50% [8] - Another company in the same industry, Immatics, is expected to report a quarterly loss of $0.50 per share, with revenues projected to decline by 77.9% year-over-year [9]

Financial Performance - The company reported 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[124]. - The net loss for the three months ended September 30, 2025, was $16.3 million, compared to a net loss of $14.0 million for the same period in 2024, indicating a decline of $2.3 million[140]. - For the nine months ended September 30, 2025, collaboration and license revenue increased by $25.5 million to $30.1 million from $4.6 million in the same period in 2024[150]. - Total operating expenses for the nine months ended September 30, 2025, were $60.2 million, compared to $51.6 million for the same period in 2024, reflecting an increase of $8.7 million[149]. - The loss from operations for the nine months ended September 30, 2025, was $30.1 million, a decrease of $16.8 million compared to a loss of $47.0 million for the same period in 2024[149]. Cash and Capital Resources - As of September 30, 2025, the company had an accumulated deficit of $429.1 million[124]. - The company had cash and cash equivalents of $103.8 million as of September 30, 2025, which, along with a $17.5 million development milestone received from Gilead, is expected to fund operations into the first quarter of 2027[125]. - Financing activities provided net cash of $51.9 million for the nine months ended September 30, 2025, compared to $21.0 million for the same period in 2024[166]. - The company anticipates substantial future capital requirements to support ongoing research and development activities, with expected continued operating losses and negative cash flows[168]. - The company filed a universal shelf registration statement to register for sale up to $250.0 million of various securities, effective May 8, 2025[160]. Revenue and Expenses - Collaboration and license revenue increased by $16.8 million from $2.3 million for the three months ended September 30, 2024, to $19.1 million for the three months ended September 30, 2025[141]. - Total revenue for the three months ended September 30, 2025, was $19.1 million, compared to $2.3 million for the same period in 2024, reflecting a significant increase[140]. - Research and development expenses rose by $3.6 million from $10.8 million for the three months ended September 30, 2024, to $14.3 million for the same period in 2025[143]. - General and administrative expenses increased by $0.4 million from $6.3 million for the three months ended September 30, 2024, to $6.7 million for the same period in 2025[143]. - General and administrative expenses increased by $4.0 million from $18.3 million in the nine months ended September 30, 2024, to $22.3 million in the same period of 2025[153]. Clinical Development - The company is advancing vilastobart in a Phase 2 clinical trial for MSS mCRC and anticipates reporting additional data in the first half of 2026[120]. - Efarindodekin alfa's Phase 2 trial for advanced solid tumors was initiated in Q3 2025, achieving a $17.5 million milestone under the agreement with Gilead[120]. - The company is actively seeking a partner to develop vilastobart in combination with PD-(L)1 or PD1-VEGF in MSS mCRC and other tumor types[120]. - The company is currently engaged in clinical trials for vilastobart and efarindodekin alfa, with ongoing preclinical development for future product candidates[175]. Market and Operational Risks - The company faces substantial doubt about its ability to continue as a going concern without securing additional capital or implementing other strategies[177]. - The company is subject to market risks, including volatility from economic conditions and potential impacts on capital access[177]. - The company is focused on the costs and timing of future commercialization activities for product candidates that receive regulatory approval[175]. Accounting and Compliance - The company has not generated any revenue from product sales since inception and does not expect to do so for at least the next several years[128]. - The company has incurred significant operating losses and will need substantial additional capital to support ongoing operations and strategies[125]. - The company recognized no restructuring expenses for the nine months ended September 30, 2025, compared to $0.9 million in the same period of 2024[154]. - There have been no material changes to the company's contractual obligations during the nine months ended September 30, 2025[178]. - The company has not made changes to its critical accounting policies, except for estimates related to the fair value of common stock warrant liabilities[179].