Company: KROS
Filing Date: 2025-05-19
Form Type: DEFA14A
Source: 0001104659-25-050243
Chunk: 0

Company: Keros Therapeutics, Inc.
Filing Date: 2025-05-19
Form: DEFA14A
Chunk 0
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<div align='center'>UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE

SECURITIES EXCHANGE ACT OF 1934</div>

Filed by the Registrant x

Filed by a Party other than the Registrant ¨

Check the appropriate box:

| ¨ | Preliminary Proxy Statement                                |
| ¨ | Confidential, for Use of the Commission Only (as permitted 
 by Rule 14a-6(e)(2))                                       |
| ¨ | Definitive Proxy Statement                                 |
| x | Definitive Additional Materials                            |
| ¨ | Soliciting Material Pursuant to §240.14a-12                |

<div align='center'>Keros Therapeutics, Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement if other than the Registrant)</div>

Payment of Filing Fee (Check the appropriate box):

| x | No fee required.                                            |
| ¨ | Fee paid previously with preliminary materials.             |
| ¨ | Fee computed on table in exhibit required by Item 25(b) per 
 Exchange Act Rule 14a-6(i)(1) and 0-11.                     |

<div align='center'>SUPPLEMENT TO PROXY STATEMENT FOR 2025 ANNUAL MEETING OF STOCKHOLDERS</div>

This proxy statement supplement (“Supplement”)
relates to the Notice of Annual Meeting of Stockholders and Proxy Statement (the “Proxy Statement”) that Keros Therapeutics, Inc.
(“we,” “us,” the “Company” or “Keros”) filed with the Securities and Exchange Commission
(the “SEC”) on April 23, 2025, and furnished to our stockholders in connection with the solicitation of proxies by our
Board of Directors (the “Board”) for the Company’s 2025 Annual Meeting of Stockholders (the “Annual Meeting”)
to be held on June 4, 2025, or at any adjournment or postponement thereof. This Supplement is being filed with the SEC and is being
made available to stockholders on or about May 19, 2025.

<div align='center'>Explanatory Note</div>

On May 8, 2025, ADAR1 Capital Management, LLC, ADAR1 Capital Management GP,