# EDGAR Filing Document

**Accession Number:** 0001664710
**File Stem:** 0000902664-25-003804
**Filing Date:** 2025-8
**Character Count:** 18052
**Document Hash:** 84762d3c89117912035c300ff6535da1
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0000902664-25-003804.hdr.sgml**: 20250821

**ACCESSION NUMBER**: 0000902664-25-003804

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13D/A

**PUBLIC DOCUMENT COUNT**: 2

**FILED AS OF DATE**: 20250821

**DATE AS OF CHANGE**: 20250821

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Keros Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001664710
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 811173868
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-91484
- **FILM NUMBER:** 251241033

**BUSINESS ADDRESS:**
- **STREET 1:** 1050 WALTHAM STREET, SUITE 302
- **CITY:** LEXINGTON
- **STATE:** MA
- **ZIP:** 02421
- **BUSINESS PHONE:** 617-314-6297

**MAIL ADDRESS:**
- **STREET 1:** 1050 WALTHAM STREET, SUITE 302
- **CITY:** LEXINGTON
- **STATE:** MA
- **ZIP:** 02421
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** ADAR1 Capital Management, LLC
- **CENTRAL INDEX KEY:** 0001940272

**ORGANIZATION NAME:**
- **EIN:** 000000000
- **STATE OF INCORPORATION:** TX
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A

**BUSINESS ADDRESS:**
- **STREET 1:** 3503 WILD CHERRY DRIVE
- **STREET 2:** BUILDING 9
- **CITY:** AUSTIN
- **STATE:** TX
- **ZIP:** 78738
- **BUSINESS PHONE:** 512-254-3790

**MAIL ADDRESS:**
- **STREET 1:** 3503 WILD CHERRY DRIVE
- **STREET 2:** BUILDING 9
- **CITY:** AUSTIN
- **STATE:** TX
- **ZIP:** 78738

## Ex-99

**ADAR1 Sends Open Letter to Keros Board of Directors Urging the Board to Engage Constructively on Strategy, Capital Allocation and Board Refreshment**

**AUSTIN, TX, August 21, 2025 (PR Newswire)** — ADAR1 Capital Management, LLC (together with its affiliates, "ADAR1" or "we"), the largest stockholder of Keros Therapeutics (Nasdaq: KROS) ("Keros" or the "Company") with approximately 13.3% of the Company's outstanding shares, today released an open letter to Keros' Board of Directors (the "Board") expressing its disappointment with the Board's refusal to engage with ADAR1 on the Company's strategy, capital allocation priorities and Board refreshment.

The full text of the letter is below.

\* \* \*

Dear Members of the Board:

In July, we wrote to the Board privately to propose an in-person meeting to discuss our ideas to maximize stockholder value. We had hoped that the broad stockholder dissatisfaction evident in the results of the 2025 Annual Meeting would prompt the Board to adopt a more constructive and conciliatory approach to its engagement with investors.

Unfortunately, that hope was misplaced. Rather than welcoming the opportunity to engage with the Company's largest stockholder, Keros' management team and Board have repeatedly declined to interact with us directly and instead referred us to the Company's financial advisor.

As we have conveyed to you (and now to your financial advisor), we believe Keros is worth significantly more than the price at which its stock trades. Its valuation is supported, in our view, by the Company's large cash balance and the net present value of the Takeda partnership for elritercept, which we believe the Company should distribute to stockholders via CVR. Given the large and persistent undervaluation of the Company's stock, we would like to work collaboratively with the Board to unlock this value for all stockholders.

In furtherance of that goal, we reiterate our request to meet with the independent directors as soon as practicable. We are available to meet at the Company's headquarters in Lexington or any other location that is convenient for you.

Additionally, we are concerned by the lack of follow-through on the Company's June 9 announcement regarding the planned return of $375 million in excess capital. Shareholders have now waited for more than two months without any update on the timing or process for the return of capital. We urge the Company to promptly communicate a clear and detailed plan to return capital, specifically through the declaration of a special dividend.

Our strong preference is to work together with the Board to help reorient the Company's strategic direction into one that benefits all shareholders. However, should the Board continue to refuse our invitations to engage, we will seek to elect new directors at the next Annual Meeting – directors who will embrace their role as fiduciaries and are willing to at least hear the perspectives of stockholders. In the meantime, we caution the Board against making any changes to its composition or to the Company's strategy without first seeking input from its major stockholders, including ADAR1.

Keros has an opportunity to build significant long-term value for its investors, but doing so requires a Board that is willing to listen to and work constructively with its stockholders. We urge you to take this opportunity to engage with us in good faith.

Sincerely,

Daniel Schneeberger

ADAR1 Capital Management

**About ADAR1 Capital Management**<br> ADAR1 Capital Management is an SEC-registered investment manager based in Austin, Texas, focused on public and private equity investments in the life sciences and biotechnology sectors. The firm was founded in October 2018 by Dr. Daniel Schneeberger, who brings over 20 years of experience spanning scientific research, healthcare consulting, institutional investing, and executive leadership in the healthcare industry. He is supported by a team of experienced professionals with deep medical and scientific expertise and a strong track record of biopharmaceutical investing.

**Contact:**<br> info@adar1.com<br> 512-254-3790

### UNITED STATES 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**<br>3503 Wild Cherry Drive, Building 9<br>Austin TX 78738<br>(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)*

| **CUSIP No.** | **492327101** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**ADAR1 Capital Management, LLC** | Name of reporting person<br>**ADAR1 Capital Management, LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**TEXAS** | Citizenship or place of organization<br>**TEXAS** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**5389264.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**5389264.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**0.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**5389264.00** | Aggregate amount beneficially owned by each reporting person<br>**5389264.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[x] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[x] | |
| 13 | Percent of class represented by amount in Row (11)<br>**13.27%** | Percent of class represented by amount in Row (11)<br>**13.27%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

**Comment for 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.

| **CUSIP No.** | **492327101** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**ADAR1 Capital Management GP, LLC** | Name of reporting person<br>**ADAR1 Capital Management GP, LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**TEXAS** | Citizenship or place of organization<br>**TEXAS** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**4645906.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**4645906.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**0.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**4645906.00** | Aggregate amount beneficially owned by each reporting person<br>**4645906.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[x] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[x] | |
| 13 | Percent of class represented by amount in Row (11)<br>**11.44%** | Percent of class represented by amount in Row (11)<br>**11.44%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

**Comment for 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.

| **CUSIP No.** | **492327101** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Daniel Schneeberger** | Name of reporting person<br>**Daniel Schneeberger** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**TEXAS** | Citizenship or place of organization<br>**TEXAS** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**5389264.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**5389264.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**0.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**5389264.00** | Aggregate amount beneficially owned by each reporting person<br>**5389264.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[x] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[x] | |
| 13 | Percent of class represented by amount in Row (11)<br>**13.27%** | Percent of class represented by amount in Row (11)<br>**13.27%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

**Comment for 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.

**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, MA, 02421

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.

### 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.

**Reporting Person:** ADAR1 Capital Management, LLC

**Signature:** /s/ Daniel Schneeberger

**Name/Title:** Daniel Schneeberger, Manager

**Date:** 08/21/2025

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.

**Reporting Person:** ADAR1 Capital Management GP, LLC

**Signature:** /s/ Daniel Schneeberger

**Name/Title:** Daniel Schneeberger, Manager

**Date:** 08/21/2025

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.

**Reporting Person:** Daniel Schneeberger

**Signature:** /s/ Daniel Schneeberger

**Name/Title:** Daniel Schneeberger

**Date:** 08/21/2025