Supplemental Prospectus (Form 424B3)

Filed Pursuant to Rule 424(b)(3)

Registration No. 333-290108

PROSPECTUS SUPPLEMENT

(To Prospectus dated September 15, 2025)

ImageneBio, Inc.

2,508,337 Shares of Common Stock

This prospectus supplement supplements the prospectus dated September 15, 2025 (the "Prospectus"), which forms a part of our registration statement on Form S-1 (No. 333-290108 ). This prospectus supplement is being filed to update and supplement the information in the Prospectus with certain information contained in our Current Reports on Form 8-K, filed with the Securities and Exchange Commission on October 10, 2025, October 22, 2025 and October 29, 2025 (collectively, the "Current Reports"). Accordingly, we have attached the Current Reports in relevant part to this prospectus supplement.

The Prospectus and this prospectus supplement relate to the proposed offer and resale or other disposition from time to time by the selling stockholders identified in this prospectus of 2,508,337 shares of common stock, par value $0.001 per share, (the "Common Stock") of ImageneBio, Inc.

Our Common Stock is listed on the Nasdaq Capital Market under the ticker symbol "IMA." On October 29, 2025, the last reported sales price of our Common Stock was $8.79 per share.

This prospectus supplement should be read in conjunction with the Prospectus, including any amendments or supplements to it, which is to be delivered with this prospectus supplement. This prospectus supplement is qualified by reference to the Prospectus, including any amendments or supplements thereto, except to the extent that the information provided by this prospectus supplement supersedes information contained in the Prospectus.

This prospectus supplement is not complete without, and may not be delivered or used except in conjunction with, the Prospectus, including any amendments or supplements to it.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described in the section titled "Risk Factors" beginning on page 6 of the Prospectus, and under similar headings in any amendments or supplements to the Prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities, or passed upon the accuracy or adequacy of this prospectus supplement. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is October 30, 2025

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): October 10, 2025

IMAGENEBIO, INC.

(Exact name of registrant as specified in its charter)

Delaware		001-40287		81-1697316
(State or other jurisdiction of incorporation)		(Commission File Number)		(I.R.S. Employer Identification No.)

12526 High Bluff Drive, Suite 345
San Diego, California		92130
(Address of principal executive offices)		(Zip Code)

Registrant's telephone number, including area code: (858) 345-6265

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, $0.001 par value		IMA		The Nasdaq Capital Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☒

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 13(a) of the Exchange Act. ☐

Item 5.02

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

On October 10, 2025, Jotin Marango, M.D., Ph.D., our Chief Financial Officer and principal financial officer, provided notice of his resignation, effective October 20, 2025. Dr. Marango's resignation was not due to any disagreement with the Company. We plan to conduct a search for Dr. Marango's replacement.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

				IMAGENEBIO, INC.
Date: October 10, 2025				By:		/s/ Kristin Yarema
						Kristin Yarema, Ph.D.
						Chief Executive Officer

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): October 21, 2025

IMAGENEBIO, INC.

(Exact name of registrant as specified in its charter)

Delaware		001-40287		81-1697316
(State or other jurisdiction of incorporation)		(Commission File Number)		(I.R.S. Employer Identification No.)

12526 High Bluff Drive, Suite 345
San Diego, California		92130
(Address of principal executive offices)		(Zip Code)

Registrant's telephone number, including area code: (858) 345-6265

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, $0.001 par value		IMA		The Nasdaq Capital Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☒

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 13(a) of the Exchange Act. ☐

Item 5.02

Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

(c)

On October 21, 2025, the board of directors of ImageneBio, Inc. (the "Company") appointed Kristin Yarema, Ph.D., the Company's Chief Executive Officer, as the Company's interim principal financial officer, effective immediately.

Dr. Yarema's biographical information is set forth under the section titled "Management" in the Company's registration statement on Form S-1 (File No. 333-290108), filed with the Securities and Exchange Commission on September 8, 2025, and is incorporated herein by reference.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

				IMAGENEBIO, INC.
Date: October 22, 2025				By:		/s/ Kristin Yarema
						Kristin Yarema, Ph.D.
						Chief Executive Officer

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d)

of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): October 23, 2025

IMAGENEBIO, INC.

(Exact name of registrant as specified in its charter)

Delaware		001-40287		81-1697316
(State or other jurisdiction of incorporation)		(Commission File Number)		(I.R.S. Employer Identification No.)

12526 High Bluff Drive, Suite 345
San Diego, California		92130
(Address of principal executive offices)		(Zip Code)

Registrant's telephone number, including area code: (858) 345-6265

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐	Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐	Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐	Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐	Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common Stock, $0.001 par value		IMA		The Nasdaq Capital Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☒

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 13(a) of the Exchange Act. ☐

Item 1.01

Entry into a Material Definitive Agreement.

On October 23, 2025, we provided written notice (the "Notice") of our election to (i) not have that certain transition services agreement, dated July 25, 2025 (the "Agreement") with Miragene Inc., an exempted company with limited liability incorporated and existing under the laws of the Cayman Islands ("Miragene"), automatically renew under the current service terms and (ii) extend the term for six months following the end of the initial term for a subset of the original services, including services related to chemistry, manufacturing and controls, translational sciences research and support (the "Miragene Extension Services"). The total fees payable to Miragene for the Miragene Extension Services are $200,000.

Item 1.02

Termination of a Material Definitive Agreement.

To the extent required by Item 1.02 of Form 8-K, the information contained in Item 1.01 is incorporated by reference herein.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

				IMAGENEBIO, INC.
Date: October 29, 2025				By:		/s/ Kristin Yarema
						Kristin Yarema, Ph.D.
						Chief Executive Officer