[SCHEDULE 13D/A] Keros Therapeutics, Inc. SEC Filing

Rhea-AI Filing Summary

ADAR1 Capital Management and related entities report beneficial ownership of 5,389,264 shares (13.27%) of Keros Therapeutics (KROS). The Schedule 13D/A (Amendment No.4) states ADAR1 issued an August 21, 2025 press release and open letter criticizing the Board's refusal to engage on strategy, capital allocation and Board refreshment and said it will seek to elect new directors at the next annual meeting if the Board continues to refuse engagement. The filing notes no transactions in the past 60 days, the reporting persons no longer hold previously reported long and short put positions, and the ownership percentage is based on 40,615,414 shares outstanding as of July 31, 2025.

Positive

• Transparent disclosure of aggregated beneficial ownership totaling 5,389,264 shares representing 13.27% of outstanding common stock
• Public escalation (August 21 press release and open letter) provides clear, documentable communication of ADAR1's concerns and intentions
• No share transactions in the past 60 days, indicating the disclosed stake was not recently increased

Negative

• Governance conflict risk: ADAR1 stated it will seek to elect new directors if the Board refuses engagement, creating potential for a contested proxy
• Potential shareholder uncertainty: Public criticism of strategy and capital allocation may increase near-term volatility in the issuer's stock
• Previously reported derivatives removed: ADAR1 no longer holds certain long and short puts, altering the composition of reported exposure

Insights

Financial Analyst

TL;DR: A 13.27% position plus a public letter signals a material, potentially activist stake with clear governance demands.

The filing discloses a sizable 13.27% beneficial ownership by ADAR1-related parties and a public escalation via an August 21 press release. That combination is a classic precursor to a proxy contest or negotiated engagement. The absence of share transactions in the past 60 days indicates the stake is presently stable rather than being built incrementally in public markets. Removal of prior long and short put positions simplifies the reported exposure to straight equity ownership. For investors, this raises governance-driven event risk and potential for near-term shareholder activism-related volatility.

Corporate Governance Expert

TL;DR: The reporter publicly demands Board engagement and threatens director elections, creating a governance dispute that may change board composition.

The Schedule 13D/A explicitly states ADAR1 criticized the Board and will seek to elect new directors if engagement is refused. That is a formal and public escalation that can force the company into negotiations or a contested proxy. The filing clarifies who holds voting and dispositive power and which entities hold the shares, improving transparency for shareholders and the company’s governance advisers. The company and its Board will need to consider response strategies and disclosure to shareholders.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)

Keros Therapeutics, Inc.

(Name of Issuer)

Common Stock, $0.0001 par value per share

(Title of Class of Securities)

492327101

(CUSIP Number)

Daniel Schneeberger
3503 Wild Cherry Drive, Building 9,
Austin, TX, 78738
(512) 254-3790

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

08/21/2025

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

CUSIP No. 492327101

1

Name of reporting person

ADAR1 Capital Management, LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

TEXAS

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 5,389,264.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 5,389,264.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

5,389,264.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

13.27 %

14

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person:

The amounts reported in boxes 7, 9 and 11 include (i) 4,391,237 shares of Common Stock held by ADAR1 Partners, LP, (ii) 743,358 shares of Common Stock held by Spearhead Insurance Solutions IDF, LLC and (iii) 254,669 shares of Common Stock held by ADAR1 SPV I, LP as of August 21, 2025. As the investment manager of ADAR1 Partners, LP and ADAR1 SPV I, LP and as the sub-advisor of Spearhead Insurance Solutions IDF, LLC, ADAR1 Capital Management, LLC may be deemed to indirectly beneficially own securities held by ADAR1 Partners, LP, ADAR1 SPV I, LP and Spearhead Insurance Solutions IDF, LLC. Amounts reported do not include shares underlying certain swap arrangements as disclosed in the Schedule 13D. The percentage in box 13 is based on 40,615,414 shares of Common Stock of the Issuer outstanding as of July 31, 2025, reported in the Issuer's Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2025, filed with the SEC on August 6, 2025.

SCHEDULE 13D

CUSIP No. 492327101

1

Name of reporting person

ADAR1 Capital Management GP, LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

TEXAS

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 4,645,906.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 4,645,906.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

4,645,906.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

11.44 %

14

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person:

The amounts reported in boxes 7, 9 and 11 include (i) 4,391,237 shares of Common Stock held by ADAR1 Partners, LP and (ii) 254,669 shares of Common Stock held by ADAR1 SPV I, LP as of August 21, 2025. As the general partner of ADAR1 Partners, LP and ADAR1 SPV I, LP, ADAR1 Capital Management GP, LLC may be deemed to indirectly beneficially own securities held by ADAR1 Partners, LP and ADAR1 SPV I, LP. Amounts reported do not include shares underlying certain swap arrangements as disclosed in the Schedule 13D. The percentage in box 13 is based on 40,615,414 shares of Common Stock of the Issuer outstanding as of July 31, 2025, reported in the Issuer's Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2025, filed with the SEC on August 6, 2025.

SCHEDULE 13D

CUSIP No. 492327101

1

Name of reporting person

Daniel Schneeberger

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

TEXAS

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 5,389,264.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 5,389,264.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

5,389,264.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

13.27 %

14

Type of Reporting Person (See Instructions)

IN

Comment for Type of Reporting Person:

The amounts reported in boxes 7, 9 and 11 include (i) 4,391,237 shares of Common Stock held by ADAR1 Partners, LP, (ii) 743,358 shares of Common Stock held by Spearhead Insurance Solutions IDF, LLC and (iii) 254,669 shares of Common Stock held by ADAR1 SPV I, LP as of August 21, 2025. As the manager of ADAR1 Capital Management, LLC and ADAR1 Capital Management GP, LLC, Mr. Schneeberger may be deemed to indirectly beneficially own securities held by ADAR1 Partners, LP, Spearhead Insurance Solutions IDF, LLC, and ADAR1 SPV I, LP. Amounts reported do not include shares underlying certain swap arrangements as disclosed in the Schedule 13D. The percentage in box 13 is based on 40,615,414 shares of Common Stock of the Issuer outstanding as of July 31, 2025, reported in the Issuer's Quarterly Report on Form 10-Q for the quarterly period ended June 30, 2025, filed with the SEC on August 6, 2025.

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, $0.0001 par value per share
(b)	Name of Issuer: Keros Therapeutics, Inc.
(c)	Address of Issuer's Principal Executive Offices: 1050 Waltham Street, Suite 302, Lexington, MASSACHUSETTS , 02421.
Item 1 Comment: This Amendment No. 4 ("Amendment No. 4") amends and supplements the statement on Schedule 13D filed with the Securities and Exchange Commission on April 11, 2025 (as amended from time to time, the "Schedule 13D"). Except as otherwise stated, the Schedule 13D remains unchanged. Capitalized terms used herein and not otherwise defined in this Amendment No. 4 have the meanings set forth in the Schedule 13D.
Item 4.	Purpose of Transaction
	On August 21, 2025, ADAR1 Capital Management issued a press release (the "August 21 Press Release"), including an open letter, expressing its disappointment with the Board's refusal to engage with ADAR1 Capital Management on the Issuer's strategy, capital allocation priorities and Board refreshment, and stating that it will seek to elect new directors at the next annual meeting of the Issuer's stockholders should the Board continue to refuse ADAR1 Capital Management's invitation to engage. The foregoing description of the August 21 Press Release does not purport to be complete and is qualified in its entirety by reference to the full text of the August 21 Press Release, which is attached hereto as Exhibit H and is incorporated herein by reference.
Item 5.	Interest in Securities of the Issuer
(a)	The information contained on the cover pages of this Amendment No. 4 is incorporated herein by reference.
(b)	The information contained on the cover pages of this Amendment No. 4 is incorporated herein by reference.
(c)	No transactions in the shares of Common Stock have been effected by the Reporting Persons during the past sixty (60) days.
Item 6.	Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer
	The Reporting Persons no longer hold the Long Puts and Short Puts previously reported in the Schedule 13D.
Item 7.	Material to be Filed as Exhibits.
	Exhibit H: August 21 Press Release

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

ADAR1 Capital Management, LLC

Signature:	/s/ Daniel Schneeberger
Name/Title:	Daniel Schneeberger, Manager
Date:	08/21/2025

ADAR1 Capital Management GP, LLC

Signature:	/s/ Daniel Schneeberger
Name/Title:	Daniel Schneeberger, Manager
Date:	08/21/2025

Daniel Schneeberger

Signature:	/s/ Daniel Schneeberger
Name/Title:	Daniel Schneeberger
Date:	08/21/2025

FAQ

How many KROS shares does ADAR1 beneficially own?

ADAR1-related reporting persons beneficially own 5,389,264 shares, equal to 13.27% of Keros Therapeutics outstanding common stock based on 40,615,414 shares.

What action did ADAR1 take on August 21, 2025 regarding KROS?

ADAR1 issued an August 21, 2025 press release and open letter expressing disappointment with the Board and stating it will seek to elect new directors if the Board refuses to engage.

Did the reporting persons trade KROS shares in the past 60 days?

No. The filing states no transactions in the shares of Common Stock were effected by the reporting persons during the past 60 days.

Are there any derivative positions reported by ADAR1 in this amendment?

The filing states the reporting persons no longer hold the Long Puts and Short Puts previously reported in the Schedule 13D.

What ownership entities are included in the ADAR1 total?

The reported total includes shares held by ADAR1 Partners, LP (4,391,237), Spearhead Insurance Solutions IDF, LLC (743,358), and ADAR1 SPV I, LP (254,669) as of August 21, 2025.