Company: IOBT
Filing Date: 2025-04-07
Form Type: S-8
Source: 0001193125-25-074645
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Company: IO Biotech, Inc.
Filing Date: 2025-04-07
Form: S-8
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As filed with the Securities and Exchange Commission on April 7, 2025 Registration No. 333- UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 IO BIOTECH, INC. (Exact name of registrant as specified in its charter)

| Delaware                        |     | 87-0909276         |
| (State or other jurisdiction of 
 incorporation or organization)  |     | -I.R.S. Employer   
 Identification No. |

Ole Maaløes Vej 3 DK-2200Copenhagen N Denmark (Address of principal executive offices) IO BIOTECH, INC. 2021 EQUITY AND INCENTIVE PLAN (Full title of the plan) Corporation Trust Company Corporation Trust Center 1209 N Orange Street Wilmington, DE 19801 (800) 677-3394 (Name, address and telephone number, including area code, of agent for service) Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-acceleratedfiler, a 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-2of the Exchange Act.

| Large accelerated filer |     | ☐ |     | Accelerated filer         |     | ☐ |
| Non-accelerated filer   |     | ☒ |     | Smaller reporting company |     | ☒ |
|                         |     |   |     | 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 7(a)(2)(B) of the Securities Act. ☐

EXPLANATORY NOTE This Registration Statement is being filed by IO Biotech, Inc. (the “Registrant”) for the purpose of registering an additional 2,635,236 shares of the Registrant’s Common Stock, par value $0.001 per share (the “Common Stock”), that were reserved for issuance under the IO Biotech, Inc. 2021 Equity and Incentive Plan. This Registration Statement on Form S-8hereby incorporates by reference