As filed with the Securities and Exchange Commission on May 7, 2026

Registration No. 333-   

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

IN8BIO, INC.

(Exact name of registrant as specified in its charter)

Amended and Restated 2023 Equity Incentive Plan

Amended and Restated 2026 Equity Incentive Plan

Non-Plan Inducement Stock Option

(Full titles of the plans)

William Ho

Chief Executive Officer

IN8bio, Inc.

350 5th Avenue, Suite 5330, New York, New York 10118

(Name and address of agent for service)

(646) 600-6438

(Telephone number, including area code, of agent for service)

Copies to:

Jaime L. Chase

Cooley LLP

1299 Pennsylvania Avenue, NW, Suite 700

Washington, DC 20004

(202) 842-7800

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

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. ☐

EXPLANATORY NOTE

Pursuant to General Instruction E of Form S-8, IN8bio, Inc. (the “Registrant”) is filing this Registration Statement with the Securities and Exchange Commission (the “Commission”) to register an aggregate of 3,408,307 shares of common stock, which consists of (i) 341,637 shares issuable upon the exercise of outstanding options granted pursuant to the Registrant’s Amended and Restated 2023 Equity Incentive Plan (the “2023 Plan”) and (ii) 3,066,670 shares of common stock reserved for future grant under the Registrant’s Amended and Restated 2026 Equity Incentive Plan (the successor plan to the 2023 Plan) (the “2026 Plan”). The 2026 Plan was approved by the Registrant’s stockholders at its annual meeting of stockholders held on May 7, 2026. As provided in the 2026 Plan, from and after the effectiveness of the 2026 Plan, any of the 341,637 shares issuable upon the exercise of outstanding options granted pursuant to the 2023 Plan that become Returning Shares (as defined in the 2026 Plan) will be available for grants of new awards under the 2026 Plan.

The Registrant is also filing this registration statement to register 11,800 shares of common stock issuable upon the exercise of outstanding options granted to two employees of the Registrant on April 1, 2026 (the “Inducement Awards”), which were granted outside of any equity compensation plan as an inducement material to the new employees entering into employment with the Registrant, in accordance with Nasdaq Listing Rule 5635(c)(4). The Inducement Awards were approved by the Registrant’s Compensation Committee in compliance with and in reliance on Nasdaq Listing Rule 5635(c)(4).

In accordance with the instructional note to Part I of Form S-8 as promulgated by the Commission, the information specified by Part I of the Form S-8 has been omitted from this Registration Statement.

PART II

INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference.

The Registrant hereby incorporates by reference into this Registration Statement the following documents filed by it with the Commission:

All documents filed by the Registrant pursuant to Section 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) subsequent to the filing of this Registration Statement and prior to the filing of a post-effective amendment which indicates that all securities offered hereby have been sold or which deregisters all securities then remaining unsold, shall be deemed to be incorporated by reference into this Registration Statement and to be a part hereof from the date of filing such documents, except as to specific sections of such documents as set forth therein. Any statement contained in a document incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or superseded for purposes of this Registration Statement to the extent that a statement herein or in any subsequently filed document which also is or is deemed to be incorporated by reference herein modifies or supersedes such statement. Any such statement so modified or superseded shall not constitute a part of this Registration Statement, except as so modified or superseded.

Item 4. Description of Securities.

Not applicable.

Item 5. Interests of Named Experts and Counsel.

As of the date hereof, GC&H Investments and GC&H Investments, LLC, each an entity that is comprised of partners and associates of Cooley LLP, beneficially own an aggregate of 5,797 shares of the Registrant’s common stock.

Item 6. Indemnification of Directors and Officers.

Section 145 of the Delaware General Corporation Law authorizes a court to award, or a corporation’s board of directors to grant, indemnity to directors and officers in terms sufficiently broad to permit such indemnification under certain circumstances for liabilities, including reimbursement for expenses incurred, arising under the Securities Act. The Registrant’s amended and restated certificate of incorporation provides for indemnification of the Registrant’s directors to the maximum extent permitted by the Delaware General Corporation Law, and the Registrant’s amended and restated bylaws provide for indemnification of the Registrant’s directors, officers, employees and other agents to the maximum extent permitted by law.

The Registrant has entered into indemnification agreements with the Registrant’s directors and officers, whereby the Registrant has agreed to indemnify the Registrant’s directors and officers to the fullest extent permitted by law, including advancement of expenses incurred in legal proceedings to which the director or officer was, or is threatened to be made, a party by reason of the fact that such director or officer is or was a director, officer, employee or agent of the Registrant, provided that such director or officer acted in good faith and in a manner that the director or officer reasonably believed to be in, or not opposed to, the best interest of the Registrant. At present, there is no pending litigation or proceeding involving a director or officer of the Registrant regarding which indemnification is sought, nor is the Registrant aware of any threatened litigation that may result in claims for indemnification.

The Registrant maintains insurance policies that indemnify the Registrant’s directors and officers against various liabilities arising under the Securities Act and the Exchange Act that might be incurred by any director or officer in his capacity as such.

Item 7. Exemption from Registration Claimed.

Not applicable.

Item 8. Exhibits.

The exhibits to this Registration Statement are listed below:

Item 9. Undertakings.

A. The undersigned Registrant hereby undertakes:

1. To file, during any period in which offers or sales are being made, a post-effective amendment to this Registration Statement:

(i) To include any prospectus required by Section 10(a)(3) of the Securities Act;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the Registration Statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the Registration Statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20% change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective Registration Statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the Registration Statement or any material change to such information in the Registration Statement;

Provided, however, that paragraphs (A)(1)(i) and (A)(1)(ii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Commission by the Registrant pursuant to Section 13 or Section 15(d) of the Exchange Act that are incorporated by reference in the Registration Statement.

2. That, for the purpose of determining any liability under the Securities Act, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered herein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

3. To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

B. The undersigned Registrant hereby undertakes that, for purposes of determining any liability under the Securities Act, each filing of the Registrant’s annual report pursuant to Section 13(a) or Section 15(d) of the Exchange Act (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to Section 15(d) of the Exchange Act) that is incorporated by reference in the Registration Statement shall be deemed to be a new registration statement relating to the securities offered herein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

C. Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the Registrant pursuant to the foregoing provisions, or otherwise, the Registrant has been advised that in the opinion of the Commission such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of New York, State of New York on May 7, 2026.

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints William Ho and Patrick McCall, and each or any one of them, his or her true and lawful attorney-in-fact and agent, with full power of substitution and resubstitution, for him or her and in his or her name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done in connection therewith, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or any of them, or their or his or her substitutes or substitute, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement on Form S-8 has been signed by the following persons in the capacities and on the dates indicated.

Exhibit 5.1

Jaime L. Chase

T: +1 202 728 7096

jchase@cooley.com

May 7, 2026

IN8bio, Inc.

350 5th Avenue

Suite 5330

New York, New York 10118

Ladies and Gentlemen:

We have acted as counsel to IN8bio, Inc., a Delaware corporation (the “Company”), in connection with the filing by the Company of a Registration Statement on Form S-8 (the “Registration Statement”) with the Securities and Exchange Commission (the “Commission”) covering the offering of up to 3,408,307 shares (the “Shares”) of the Company’s common stock, $0.0001 par value per share (the “Common Stock”), consisting of (i) 341,637 shares of Common Stock issuable pursuant to the Company’s Amended and Restated 2023 Equity Incentive Plan (the “2023 Plan”), (ii) 3,066,670 shares of Common Stock issuable pursuant to the Company’s Amended and Restated 2026 Equity Incentive Plan (the “2026 Plan”) and (iii) 11,800 shares of common stock issuable under inducement stock option awards granted by the Company pursuant to the terms of a stock option grant notice and stock option agreement (together with the 2023 Plan and the 2026 Plan, the “Plans”).

In connection with this opinion, we have examined and relied upon (i) the Registration Statement and related prospectuses, (ii) the Company’s certificate of incorporation and bylaws, each as currently in effect, (iii) the Plans and (iv) such other records, documents, opinions, certificates, memoranda and instruments as in our judgment are necessary or appropriate to enable us to render the opinion expressed below. We have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the conformity to originals of all documents submitted to us as copies, the accuracy, completeness and authenticity of certificates of public officials and the due authorization, execution and delivery of all documents by all persons other than the Company. As to certain factual matters, we have relied upon a certificate of an officer of the Company and have not independently verified such matters.

Our opinion is expressed only with respect to the General Corporation Law of the State of Delaware. We express no opinion to the extent that any other laws are applicable to the subject matter hereof and express no opinion and provide no assurance as to compliance with any federal or state law, rule or regulation.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the Shares, when sold and issued in accordance with the Plans, the Registration Statement and the related prospectuses, will be validly issued, fully paid and nonassessable (except as to shares issued pursuant to deferred payment arrangements, which will be fully paid and nonassessable when such deferred payments are made in full).

Our opinion is limited to the matters expressly set forth in this letter, and no opinion has been or should be implied, or may be inferred, beyond the matters expressly stated. This opinion speaks only as to law and facts in effect or existing as of the date hereof, and we have no obligation or responsibility to update or supplement this letter to reflect any facts or circumstances that may hereafter come to our attention or any changes in law that may hereafter occur.

Cooley LLP 1299 Pennsylvania Ave., Washington DC 20004

t: (212) 842-7800 f: (202) 842-7899 cooley.com

Page Two

May 7, 2026

We consent to the filing of this opinion as an exhibit to the Registration Statement. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act of 1933, as amended, or the rules and regulations of the Commission thereunder.

Cooley LLP 1299 Pennsylvania Ave., Washington DC 20004

t: (212) 842-7800 f: (202) 842-7899 cooley.com

Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the Registration Statement on Form S-8 of our report dated March 12, 2026, with respect to the financial statements of IN8bio, Inc. as of December 31, 2025 and 2024, and for the years then ended, which report is included in the Annual Report on Form 10-K of IN8bio, Inc. for the year ended December 31, 2025 filed with the Securities and Exchange Commission. Our audit report includes an explanatory paragraph relating to IN8bio, Inc.’s ability to continue as a going concern.

/s/ CohnReznick LLP

New York, New York

May 7, 2026