Instil Bio, Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

For the fiscal year ended December 31, 2025

OR

For the transition period from ________ to ________

Commission file number 001-40215

Instil Bio, Inc.

(Exact name of registrant as specified in its charter)

(972)499-3350

Registrant’s telephone number, including area code

Not Applicable

(Former name, former address and former fiscal year, if changed since last report)

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes☐ No ☒

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes☐ No ☒

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports); and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No☐

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate web site, if any, every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit files). Yes ☒ No☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.☐

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report.☐

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements.☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to § 240.10D-1(b).☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes☐ No☒

As of June 30, 2025, the last business day of the registrant’s most recently completed second fiscal quarter, the aggregate market value of the registrant’s common stock held by non-affiliates of the registrant was approximately $83.4 million, based on the closing price of the registrant’s common stock on the Nasdaq Stock Market on June 30, 2025 of $20.83 per share.

Indicate the number of shares outstanding of each of the issuer’s classes of common stock, as of the latest practicable date:

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission (SEC) subsequent to the date hereof pursuant to Regulation 14A in connection with the registrant’s 2026 Annual Meeting of Stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K. Such proxy statement will be filed with the SEC not later than 120 days after the conclusion of the registrant’s fiscal year ended December 31, 2025.

TABLE OF CONTENTS

Special Note Regarding Forward-Looking Statements

This Annual Report contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this Annual Report, including statements regarding our strategy, future operations, future financial position, future revenue, projected costs, prospects, plans, and objectives of management, are forward-looking statements. In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “would,” “expect,” “plan,” “anticipate,” “could,” “might,” “intend,” “target,” “ongoing,” “project,” “estimate,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions intended to identify statements about the future. These statements speak only as of the date of this Annual Report and involve known and unknown risks, uncertainties and other important factors that may cause our actual results, levels of activity, performance or achievements to be materially different from any future results, levels of activity, performance or achievements expressed or implied by the forward-looking statements. We have based these forward-looking statements largely on our current expectations and projections about future events and financial trends that we believe may affect our business, financial condition and results of operations. These forward-looking statements include, without limitation, statements about:

•our ability to in-license or acquire and develop additional novel therapeutic candidates;

•our estimates of our expenses, ongoing losses, future revenue, capital requirements and our need for or ability to obtain additional funding;

•our ability to establish or maintain collaborations or strategic relationships;

•our ability to identify, recruit and retain key personnel, including executive officers and members of management;

•our reliance upon intellectual property licensed from third parties and our ability to obtain such licenses on commercially reasonable terms or at all;

•our ability to protect and enforce our intellectual property position for any product candidates we may in-license or acquire, and the scope of such protection;

•our financial performance;

•the period over which we estimate our existing cash, cash equivalents and marketable securities will be sufficient to fund our future operating expenses and capital expenditure requirements;

•our ability to continue as a going concern;

•our competitive position and the development of and projections relating to our competitors or our industry;

•the impact of laws and regulations;

•our expectations regarding the time during which we will be an emerging growth company under the Jumpstart Our Business Startups Act of 2012;

•the impact of economic conditions, including increases in interest rates, inflation, and foreign and domestic tariffs, on the costs of raw materials, wages, manufacturing and clinical trials and on borrowing costs; and

•the timing and anticipated amounts of future tax payments and benefits (including the potential recognition of unrecognized tax benefits), as well as timing of conclusion of tax audits.

You should read this Annual Report and the documents that we have filed as exhibits to this Annual Report completely and with the understanding that our actual future results may be materially different from what we expect. The forward-looking statements contained in this Annual Report are made as of the date of this Annual Report, and we do not assume any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by applicable law. We have included important factors in this Annual Report, particularly in the “Risk Factor Summary” and “Risk Factors” sections, that could cause actual results or events to differ materially from the forward-looking statements that we make.

Risk Factor Summary

Investing in our securities involves a high degree of risk. Below is a summary of material factors that make an investment in our securities speculative or risky. Importantly, this summary does not address every aspect of our risk factors, all of the risks that we face, or other factors not presently known to us or that we currently believe are immaterial. Additional discussion of the risks summarized in this Risk Factor Summary, as well as other risks that we face, can be found under the heading “Risk Factors” in Part I of this Annual Report.

Our business is subject to a number of risks of which you should be aware before making a decision to invest in our common stock. These risks include, among others, the following:

•We have incurred significant losses since our inception and have identified an indicator of substantial doubt about our ability to continue as a going concern. We expect to incur losses for the foreseeable future and may never achieve or maintain profitability.

•We have a limited operating history and no history of completing any clinical trial or commercializing any product, which may make it difficult for an investor to evaluate the success of our business to date and to assess our future viability.

•We will need substantial additional funding to meet our financial obligations and to pursue our business objectives. If we are unable to raise capital when needed, we could be forced to delay or curtail our planned operations and the pursuit of our strategy.

•We currently do not have a product candidate in active development. We have, and we may in the future, engage in strategic transactions to license or otherwise acquire new product candidates or technologies, and we may not be successful in licensing or otherwise acquiring new product candidates, or in developing or commercializing any such product candidates.

•The regulatory approval processes of the U.S. Food and Drug Administration, or FDA, Medicines and Healthcare Products Regulatory Agency, or MHRA, European Medicines Agency, or EMA, and comparable foreign authorities are lengthy, time consuming and inherently unpredictable. If we are not able to obtain required regulatory approval for any product candidate we may seek to develop, our business will be substantially harmed.

•Success in preclinical studies or earlier clinical trials may not be indicative of results in future clinical trials. Any product candidates we may seek to develop may not have favorable results in later clinical trials, if any, or receive regulatory approval.

•Therapeutic product candidates can be complex and difficult to manufacture. We intend to rely on third parties to produce clinical supply of any product candidates we may seek to develop, and commercial supplies of any approved product. This reliance on third parties increases the risk that we will not have sufficient quantities of our product candidates or any approved products or such quantities at an acceptable cost or quality, which could delay, prevent or impair our development or commercialization efforts.

•We face significant competition from other biotechnology and pharmaceutical companies, and from non-profit institutions, which may result in others acquiring, discovering, developing or commercializing products before or more successfully than we do.

•If we or our future licensors are unable to obtain and maintain sufficient patent protection for any product candidate we may seek to develop, or if the scope of the patent protection is not sufficiently broad, third parties, including our potential competitors, could develop and commercialize products similar or identical to ours, and our ability to commercialize such product candidates may be adversely affected.

•Third parties may initiate legal proceedings alleging that we are infringing their intellectual property rights, the outcome of which would be uncertain.

•We are subject to a variety of stringent and evolving laws, regulations, rules, contractual obligations, policies and other obligations related to data privacy and data security, and our actual or perceived failure to comply with them could lead to regulatory investigations or actions; litigation; fines and penalties; disruptions of our business operations; reputational harm; loss of revenue or profits and other adverse business consequences.