Company: KROS
Filing Date: 2025-11-19
Form Type: SC TO-I/A
Source: 0001104659-25-113880
Chunk: 1

Company: Keros Therapeutics, Inc.
Filing Date: 2025-11-19
Form: SC TO-I/A
Chunk 1
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 provision(s) relied upon:

| ¨ | Rule 13e-4(i) (Cross-Border 
 Issuer Tender Offer)        |
| ¨ | Rule 14d-1(d) (Cross-Border 
 Third-Party Tender Offer)   |

<div align='center'>INTRODUCTION</div>

This Amendment No. 1
(this “Amendment”) amends and supplements the Tender Offer Statement on Schedule TO (the “Schedule TO”) originally
filed with the Securities and Exchange Commission on October 20, 2025 relating to the offer by Keros Therapeutics, Inc., a Delaware
corporation (the “Company”), to purchase for cash up to an aggregate of 10,950,165 shares of its common stock, par value $0.0001
per share, for an aggregate purchase price of up to $194.4 million, at a purchase price of $17.75 per share, less any applicable withholding
taxes and without interest, upon the terms and subject to the conditions set forth in the Offer to Purchase dated October 20, 2025
(the “Offer to Purchase”) and in the related Letter of Transmittal (the “Letter of Transmittal” and, together
with the Offer to Purchase, as they may be amended or supplemented from time to time, the “Tender Offer”), copies of which
were previously filed as Exhibits (a)(1)(A) and (a)(1)(B), respectively, to the Schedule TO.

This Amendment is intended
to satisfy the reporting requirements of Rule 13e-4(c)(4) under the Securities Exchange Act of 1934, as amended. Only those
items amended are reported in this Amendment. Except as specifically provided herein, the information contained in the Schedule TO remains
unchanged and this Amendment does not modify any of the information previously reported on the Schedule TO. This Amendment should be read
in conjunction with the Schedule TO and all of the exhibits thereto, including the Offer to Purchase and the Letter of Transmittal, as
each may be amended or supplemented from time to time.

ITEM 11. ADDITIONAL INFORMATION.

Item 11 of the Schedule TO
is hereby amended and supplemented by adding the following:

“On November 19,
2025, the Company issued a press release announcing the preliminary results of the Tender Offer, which expired at 5:00 p.m., New York
City time, on Tuesday, November 18, 202