RA Capital (CLYM) details 33% Climb Bio stake and new board designee

Rhea-AI Filing Summary

RA Capital Management and affiliates updated their ownership disclosure in Climb Bio, Inc., reporting a sizable stake and a board change. The reporting group beneficially owns 23,249,186 shares of common stock, representing 33.0% of the company, including shares underlying pre-funded warrants and stock options exercisable within 60 days.

The filing explains that RA Capital advises multiple funds and accounts that hold Climb Bio securities and has delegated voting and investment power over those positions. A "Beneficial Ownership Blocker" in the pre-funded warrants limits exercises so the group cannot exceed 33.0% ownership. The amendment also notes that on June 29, 2026, RA Capital analyst Dr. Breanna Celebi was appointed to Climb Bio’s board of directors as RA Capital’s designee, replacing Dr. Andrew Levin, who resigned the same day. Additionally, on July 2, 2026, Sera Medicines made a pro rata in-kind distribution of 2,479,872 Climb Bio shares to its members, with RA Capital funds receiving portions of those shares.

Key Figures

Beneficial ownership: 23,249,186 shares Ownership percentage: 33.0% Fund ownership: 16,934,205 shares +5 more

8 metrics

Beneficial ownership 23,249,186 shares Shares of Climb Bio common stock beneficially owned by reporting persons

Ownership percentage 33.0% Percent of Climb Bio common stock class represented by 23,249,186 shares

Fund ownership 16,934,205 shares Shares beneficially owned by RA Capital Healthcare Fund, 24.1% of class

Nexus Fund III ownership 3,671,766 shares Shares beneficially owned by RA Capital Nexus Fund III, 6.4% of class

Shares outstanding 57,263,023 shares Climb Bio common stock outstanding as of May 14, 2026

Pre-funded warrants 22,546,000 shares Shares of common stock underlying pre-funded warrants held by the Fund

In-kind distribution 2,479,872 shares Climb Bio shares distributed in kind by Sera Medicines to its members

Option grant size 70,284 shares at $13.36 Total shares under Dr. Celebi’s stock option, vesting monthly from June 29, 2026

Key Terms

Beneficial Ownership Blocker, pre-funded warrants, in-kind distribution, vest stock option, +2 more

6 terms

Beneficial Ownership Blocker financial

"The Pre-Funded Warrants contain a provision (the "Beneficial Ownership Blocker") which precludes exercise..."

A beneficial ownership blocker is a legal or structural device that prevents a shareholder from being treated as the ultimate owner of enough shares to trigger control, reporting, or voting thresholds. Think of it like a speed bump that stops an investor from reaching a stake size that would force corporate disclosure or change control rights. Investors care because it affects who controls the company, how shares vote, regulatory filings, takeover risk and therefore potential value or liquidity of their holdings.

pre-funded warrants financial

"pre-funded warrants (the "Pre-Funded Warrants") exercisable for up to 22,546,000 shares of common stock..."

Pre-funded warrants are financial instruments that give investors the right to purchase a company's stock at a set price, but with most or all of the purchase price paid upfront. They function like a coupon or gift card for stock, allowing investors to buy shares later at a fixed price, which can be beneficial if they want to avoid future price increases. This makes them important for investors seeking flexibility and certainty in their investment plans.

in-kind distribution financial

"Sera made a pro rata in-kind distribution for no additional consideration of 2,479,872 shares of common stock..."

vest stock option financial

"Vest Stock Option (Right to Buy) RA Capital 07/29/2026 1,952..."

Registration Statement on Form S-3 regulatory

"as reported in the Issuer's Registration Statement on Form S-3 filed with the SEC on May 29, 2026..."

A registration statement on Form S‑3 is a short, standardized filing a qualified public company uses to register new securities with regulators so they can be sold to investors; think of it as a pre-approved, reusable permission slip that speeds up future offerings. It matters to investors because it lets the company raise money more quickly and cheaply — which can fund growth or pay debt — but may also lead to share dilution or change in ownership, so it affects value and liquidity.

Section 13(d) of the Act regulatory

"may be deemed a beneficial owner, for purposes of Section 13(d) of the Act..."

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Available on EDGAR 07/07/2026 - 04:42 PM Accepted by SEC EDGAR 07/07/2026 - 04:41 PM Learn about SEC filing dates

FAQ

What ownership stake does RA Capital report in Climb Bio (CLYM)?

RA Capital and related reporting persons beneficially own 23,249,186 shares of Climb Bio common stock, representing 33.0% of the company. This figure includes shares, pre-funded warrants, and options exercisable within 60 days, based on 57,263,023 shares outstanding as of May 14, 2026.

How many Climb Bio shares are outstanding according to this filing for CLYM?

The filing states that Climb Bio had 57,263,023 shares of common stock outstanding as of May 14, 2026. Ownership percentages, including RA Capital’s 33.0% stake, are calculated using this share count and giving effect to certain exercisable pre-funded warrants and stock options.

What is the Beneficial Ownership Blocker affecting RA Capital’s Climb Bio (CLYM) warrants?

Pre-funded warrants held by RA Capital’s fund include a Beneficial Ownership Blocker that prevents exercises if ownership would exceed 33.0% of Climb Bio’s outstanding common stock. As a result, the fund cannot exercise warrants beyond 23,249,186 beneficially owned shares.

Which RA Capital entities hold Climb Bio (CLYM) securities and in what amounts?

Holdings include 3,837,101 shares and pre-funded warrants for up to 22,546,000 shares in the healthcare fund, 1,226,497 shares in Nexus Fund, 483,679 in Nexus Fund II, 3,671,766 in Nexus Fund III, and 841,087 shares in a separately managed account.

What board change at Climb Bio (CLYM) is disclosed for RA Capital?

On June 29, 2026, RA Capital analyst Dr. Breanna Celebi was appointed to Climb Bio’s board of directors as RA Capital’s designee. She replaced Dr. Andrew Levin, who resigned from the board effective the same date, reflecting a change in RA Capital’s board representation.

What in-kind share distribution involving Climb Bio (CLYM) is described?

On July 2, 2026, Sera Medicines, LLC made a pro rata in-kind distribution of 2,479,872 Climb Bio shares to its members. From this, RA Capital’s healthcare fund received 433,672 shares and RA Capital Nexus Fund III received 805,391 shares, for no additional consideration.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 10)

Climb Bio, Inc.

(Name of Issuer)

Common Stock, par value $0.0001 per share

(Title of Class of Securities)

28658R106

(CUSIP Number)

Peter Kolchinsky
RA Capital Management, L.P., 200 Berkeley Street, 18th Floor
Boston, MA, 02116
617.778.2500

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

07/02/2026

(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).

schemaVersion:

SCHEDULE 13D

CUSIP Number(s): 28658R106

1

Name of reporting person

RA Capital Management, L.P.

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

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 23,249,186.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 23,249,186.00

11

Aggregate amount beneficially owned by each reporting person

23,249,186.00

12

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

13

Percent of class represented by amount in Row (11)

33.0 %

14

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13D

CUSIP Number(s): 28658R106

1

Name of reporting person

Peter Kolchinsky

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

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 23,249,186.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 23,249,186.00

11

Aggregate amount beneficially owned by each reporting person

23,249,186.00

12

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

13

Percent of class represented by amount in Row (11)

33.0 %

14

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13D

CUSIP Number(s): 28658R106

1

Name of reporting person

Rajeev Shah

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

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 23,249,186.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 23,249,186.00

11

Aggregate amount beneficially owned by each reporting person

23,249,186.00

12

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

13

Percent of class represented by amount in Row (11)

33.0 %

14

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13D

CUSIP Number(s): 28658R106

1

Name of reporting person

RA Capital Healthcare Fund, L.P.

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)

WC

5

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

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 16,934,205.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 16,934,205.00

11

Aggregate amount beneficially owned by each reporting person

16,934,205.00

12

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

13

Percent of class represented by amount in Row (11)

24.1 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

CUSIP Number(s): 28658R106

1

Name of reporting person

RA Capital Nexus Fund III, L.P.

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)

WC

5

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

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 3,671,766.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 3,671,766.00

11

Aggregate amount beneficially owned by each reporting person

3,671,766.00

12

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

13

Percent of class represented by amount in Row (11)

6.4 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock, par value $0.0001 per share
(b)	Name of Issuer: Climb Bio, Inc.
(c)	Address of Issuer's Principal Executive Offices: 20 William Street, Suite 145, Wellesley Hills, MASSACHUSETTS , 02481.
Item 1 Comment: This Amendment No. 10 (this "Amendment No. 10" or this "Schedule 13D/A") amends and supplements the statement on Schedule 13D originally filed with the Securities and Exchange Commission (the "SEC") on August 19, 2021, and amended on April 10, 2023, November 17, 2023, March 18, 2024, April 12, 2024, May 17, 2024, June 6, 2024, July 1, 2024, December 15, 2025 and April 29, 2026 (as amended, the "Statement") by RA Capital Management, L.P. ("RA Capital"), Peter Kolchinsky, Rajeev Shah, RA Capital Healthcare Fund, L.P. (the "Fund"), RA Capital Nexus Fund III, L.P. (the "Nexus Fund III") and Sera Medicines, LLC ("Sera"). Unless otherwise defined herein, capitalized terms used in this Amendment No. 10 shall have the meanings ascribed to them in the Statement. Unless amended or supplemented below, the information in the Statement remains unchanged.
Item 2.	Identity and Background
(a)	This Schedule 13D/A is being filed on behalf of RA Capital, Dr. Kolchinsky, Mr. Shah, the Fund and the Nexus Fund III. The foregoing entities and individuals are collectively referred to herein as the "Reporting Persons." The agreement among the Reporting Persons to file this Schedule 13D/A jointly in accordance with Rule 13d-1(k) of the Securities Exchange Act of 1934, as amended, (the "Act") is attached hereto as Exhibit 99.1. The Reporting Persons' beneficial ownership of the Issuer's securities includes (i) 3,837,101 shares of common stock held directly by the Fund, (ii) pre-funded warrants (the "Pre-Funded Warrants") exercisable for up to 22,546,000 shares of common stock held directly by the Fund; (iii) 1,226,497 shares of common stock held directly by RA Capital Nexus Fund, L.P. (the "Nexus Fund"); (iv) 483,679 shares of common stock held directly by RA Capital Nexus Fund II, L.P. (the "Nexus Fund II"); (v) 3,671,766 shares of common stock held directly by the Nexus Fund III; (vi) 841,087 shares of common stock held directly by a separately managed account (the "Account"); (vii) 90,000 vested stock options (right to buy) held by Dr. Levin for the benefit of RA Capital; and (viii) 3,904 stock options (right to buy) scheduled to vest within 60 days of this filing held by Dr. Celebi for the benefit of RA Capital. The Pre-Funded Warrants contain a provision (the "Beneficial Ownership Blocker") which precludes exercise of the Pre-Funded Warrants to the extent that, following exercise, the Fund, together with its affiliates and other attribution parties, would own more than 33.0% of the common stock outstanding. The Fund is currently prohibited from exercising the Pre-Funded Warrants to the extent that such exercise would result in the Reporting Persons' beneficial ownership of more than 23,249,186 shares of common stock. RA Capital Healthcare Fund GP, LLC is the general partner of the Fund, RA Capital Nexus Fund GP, LLC is the general partner of the Nexus Fund, RA Capital Nexus Fund II GP, LLC is the general partner of the Nexus Fund II, and RA Capital Nexus Fund III GP, LLC is the general partner of the Nexus Fund III. The general partner of RA Capital is RA Capital Management GP, LLC, of which Dr. Kolchinsky and Mr. Shah are the controlling persons. RA Capital serves as investment adviser for the Fund, the Nexus Fund, the Nexus Fund II, the Nexus Fund III and the Account and may be deemed a beneficial owner, for purposes of Section 13(d) of the Act of any securities of the Issuer held by the Fund, the Nexus Fund, the Nexus Fund II, the Nexus Fund III or the Account. The Fund, the Nexus Fund, the Nexus Fund II and the Nexus Fund III have delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in the Fund, the Nexus Fund, the Nexus Fund II and the Nexus Fund III, and each of these funds has divested themselves of voting and investment power over the reported securities they hold and may not revoke that delegation on less than 61 days' notice. The Fund, the Nexus Fund, the Nexus Fund II and the Nexus Fund III disclaim beneficial ownership of the securities they hold for purposes of Section 13(d) of the Act and therefore disclaim any obligation to report ownership of the reported securities under Section 13(d) of the Act. As managers of RA Capital, Dr. Kolchinsky and Mr. Shah may be deemed beneficial owners, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of the securities reported in this Schedule 13D/A other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of the Schedule 13D/A shall not be deemed an admission that either RA Capital, Dr. Kolchinsky, or Mr. Shah is the beneficial owner of such securities for any other purpose.
(b)	The address of the principal business office of each of the Reporting Persons is 200 Berkeley Street, 18th Floor, Boston, MA 02116.
(c)	The Fund and the Nexus Fund III are private investment vehicles. RA Capital provides investment management services to the Fund, the Nexus Fund, the Nexus Fund II, the Nexus Fund III and the Account. The principal occupation of Dr. Kolchinsky and Mr. Shah is investment management.
(d)	During the last five years, none of the Reporting Persons has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).
(e)	During the last five years, none of the Reporting Persons has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree of final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.
(f)	See Item 6 of the cover pages.
Item 4.	Purpose of Transaction
	Item 4 of the Statement is hereby amended and supplemented as follows: On June 29, 2026 Dr. Breanna Celebi (O'Reilly), an Analyst of RA Capital, was appointed to the Board of Directors of the Issuer as the designee of RA Capital, replacing Dr. Andrew Levin, who resigned from the Board of Directors effective June 29, 2026.
Item 5.	Interest in Securities of the Issuer
(a)	Rows 11 and 13 of each Reporting Person's cover page to this Schedule 13D/A set forth the aggregate number of shares of common stock and percentages of the shares of common stock beneficially owned by such Reporting Person and are incorporated by reference. The percentage set forth in each row 13 is based upon 57,263,023 shares of common stock outstanding as of May 14, 2026, as reported in the Issuer's Registration Statement on Form S-3 filed with the SEC on May 29, 2026, and giving effect to stock options and Pre-Funded Warrants, to the extent exercisable within 60 days hereof, as referenced herein.
(b)	Rows 7 through 10 of each Reporting Person's cover page to this Schedule 13D/A set forth the number of shares of common stock as to which such Reporting Person has the sole or shared power to vote or direct the vote and sole or shared power to dispose or to direct the disposition and are incorporated by reference.
(c)	On July 2, 2026, Sera made a pro rata in-kind distribution for no additional consideration of 2,479,872 shares of common stock to its members. Of the shares distributed by Sera, the Fund and the Nexus Fund III received 433,672 shares and 805,391 shares, respectively. Except as set forth above and in the table below, none of the Reporting Persons has effected any transactions with respect to the securities of the Issuer during the past sixty days. Reporting No. Price Per Transaction Person Date Shares Share Vest Stock Option (Right to Buy) RA Capital 07/29/2026 1,952 (1) (2) Vest Stock Option (Right to Buy) RA Capital 08/29/2026 1,952 (1) (2) (1) This option represents a right to purchase a total of 70,284 shares of the Issuer's common stock, which shall vest in thirty-six equal monthly installments from June 29, 2026, subject to Dr. Celebi's continuous service to the Issuer through each such vesting date. These options have an exercise price of $13.36. (2) Represents future vesting options within 60 days from the filing date of this Schedule 13D/A.
(d)	No person (other than the Reporting Persons) is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the securities subject to this Schedule 13D/A.
(e)	Not applicable.
Item 7.	Material to be Filed as Exhibits.
	Exhibit 99.1 Joint Filing Agreement

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.

RA Capital Management, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By Peter Kolchinsky, Authorized Signatory
Date:	07/07/2026

Peter Kolchinsky

Signature:	/s/ Peter Kolchinsky
Name/Title:	Peter Kolchinsky
Date:	07/07/2026

Rajeev Shah

Signature:	/s/ Rajeev Shah
Name/Title:	Rajeev Shah
Date:	07/07/2026

RA Capital Healthcare Fund, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By RA Capital Healthcare Fund GP, LLC, its General Partner, By Peter Kolchinsky, Manager
Date:	07/07/2026

RA Capital Nexus Fund III, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By RA Capital Nexus Fund III GP, LLC, its General Partner, By Peter Kolchinsky, Manager
Date:	07/07/2026