Obsidian Therapeutics, Inc. received a Schedule 13G from RA Capital Management, L.P. and related entities reporting a beneficial ownership of 5,957,103 shares of common stock. This represents 9.7% of Obsidian’s 61,727,211 shares outstanding as of August 3, 2026.
The reported position is held across several RA Capital-advised funds: 4,951,187 shares are directly held by RA Capital Healthcare Fund, L.P., 849,673 shares by RA Capital Nexus Fund II, L.P., and 156,243 shares by RA Capital Nexus Fund IV, L.P. RA Capital has been delegated sole voting and dispositive power over these shares, while the individual funds and managers, including Peter Kolchinsky and Rajeev Shah, disclaim beneficial ownership except for Section 13(d) reporting purposes.
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Key Figures
Shares beneficially owned:5,957,103 sharesOwnership percentage:9.7 %Shares outstanding:61,727,211 shares+4 more
7 metrics
Shares beneficially owned5,957,103 sharesTotal Obsidian common stock reported by RA Capital and related reporting persons
Ownership percentage9.7 %Percent of Obsidian common stock class beneficially owned by each main reporting person
Shares outstanding61,727,211 sharesObsidian common stock outstanding as of August 3, 2026
RA Capital Healthcare Fund holdings4,951,187 sharesObsidian shares directly held by RA Capital Healthcare Fund, L.P.
Nexus Fund II holdings849,673 sharesObsidian shares directly held by RA Capital Nexus Fund II, L.P.
Nexus Fund IV holdings156,243 sharesObsidian shares directly held by RA Capital Nexus Fund IV, L.P.
Shared voting power5,957,103 sharesShares over which RA Capital and principals report shared voting power
Key Terms
beneficial ownership, shared voting power, shared dispositive power, Section 13(d) of the Act, +1 more
5 terms
beneficial ownershipfinancial
"Row 9 of each Reporting Person's cover page sets forth the aggregate number of shares of common stock ... beneficially owned"
Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.
shared voting powerfinancial
"Shared Voting Power 5,957,103.00"
Shared voting power occurs when two or more parties jointly have the right to vote or decide how a block of company shares is cast, like co-owners who must agree before moving a piece of furniture. Investors care because who controls voting rights affects board elections, major corporate decisions and takeover outcomes, and shared control can alter regulatory disclosures and the practical influence any holder has over a company’s direction and value.
shared dispositive powerfinancial
"Shared Dispositive Power 5,957,103.00"
Section 13(d) of the Actregulatory
"may be deemed a beneficial owner, for purposes of Section 13(d) of the Act"
Schedule 13Gregulatory
"The Reporting Persons expressly disclaim status as a "group" for purposes of this"
A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.
FAQ
What ownership stake in Obsidian Therapeutics (OBX) does RA Capital report?
RA Capital and related entities report beneficial ownership of 5,957,103 shares of Obsidian Therapeutics common stock, representing 9.7% of the outstanding shares based on 61,727,211 shares outstanding as of August 3, 2026.
How are RA Capital’s Obsidian Therapeutics (OBX) shares allocated among its funds?
The filing states that 4,951,187 shares are held by RA Capital Healthcare Fund, L.P., 849,673 shares by RA Capital Nexus Fund II, L.P., and 156,243 shares by RA Capital Nexus Fund IV, L.P., all with voting and dispositive power delegated to RA Capital.
What percentage of Obsidian Therapeutics (OBX) does each RA Capital reporting person beneficially own?
RA Capital Management, L.P., Peter Kolchinsky, and Rajeev Shah each report 5,957,103 shares beneficially owned, equal to 9.7% of Obsidian’s common stock, with shared voting and dispositive power over these shares.
How many Obsidian Therapeutics (OBX) shares were outstanding for the ownership calculation?
The reported ownership percentages are based on 61,727,211 shares of Obsidian Therapeutics common stock outstanding as of August 3, 2026, as referenced from the company’s Form 8-K filed with the SEC on that date.
Who has voting and dispositive power over RA Capital’s Obsidian Therapeutics (OBX) shares?
The funds delegated to RA Capital the sole power to vote and dispose of all portfolio securities, including Obsidian shares. The funds disclaim beneficial ownership because they have divested voting and investment power and cannot revoke this delegation on less than 61 days’ notice.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
Obsidian Therapeutics, Inc.
(Name of Issuer)
Common Stock, par value $0.001 per share
(Title of Class of Securities)
67448A106
(CUSIP Number)
08/03/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
67448A106
1
Names of Reporting Persons
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
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
5,957,103.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
5,957,103.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
5,957,103.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
9.7 %
12
Type of Reporting Person (See Instructions)
IA, PN
SCHEDULE 13G
CUSIP Number(s):
67448A106
1
Names of Reporting Persons
Peter Kolchinsky
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
5,957,103.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
5,957,103.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
5,957,103.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
9.7 %
12
Type of Reporting Person (See Instructions)
HC, IN
SCHEDULE 13G
CUSIP Number(s):
67448A106
1
Names of Reporting Persons
Rajeev Shah
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
5,957,103.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
5,957,103.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
5,957,103.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
9.7 %
12
Type of Reporting Person (See Instructions)
HC, IN
SCHEDULE 13G
CUSIP Number(s):
67448A106
1
Names of Reporting Persons
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
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
4,951,187.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
4,951,187.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
4,951,187.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
8.0 %
12
Type of Reporting Person (See Instructions)
PN
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
Obsidian Therapeutics, Inc.
(b)
Address of issuer's principal executive offices:
1030 Massachusetts Avenue, Cambridge, MA, 02138.
Item 2.
(a)
Name of person filing:
The names of the persons filing this report (collectively, the "Reporting Persons") are:
RA Capital Management, L.P. ("RA Capital")
Peter Kolchinsky ("Dr. Kolchinsky")
Rajeev Shah ("Mr. Shah")
RA Capital Healthcare Fund, L.P. (the "Fund")
The Reporting Persons expressly disclaim status as a "group" for purposes of this Schedule 13G.
(b)
Address or principal business office or, if none, residence:
The address of the principal business office of each of the Reporting Persons is:
c/o RA Capital Management, L.P., 200 Berkeley Street, 18th Floor, Boston MA 02116
(c)
Citizenship:
RA Capital and the Fund are Delaware limited partnerships.
Dr. Kolchinsky and Mr. Shah are United States citizens.
(d)
Title of class of securities:
Common Stock, par value $0.001 per share
(e)
CUSIP Number(s):
67448A106
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.
Ownership
(a)
Amount beneficially owned:
Row 9 of each Reporting Person's cover page to this Schedule 13G sets forth the aggregate number of shares of common stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
The Reporting Persons' beneficial ownership of the Issuer's common stock consists of (i) 4,951,187 shares of common stock directly held by the Fund; (ii) 849,673 shares of common stock directly held by the RA Capital Nexus Fund II, L.P. (the "Nexus Fund II"); and (iii) 156,243 shares of common stock directly held by the RA Capital Nexus Fund IV, L.P. (the "Nexus Fund IV").
RA Capital Healthcare Fund GP, LLC is the general partner of the Fund, RA Capital Nexus Fund II GP, LLC is the general partner of the Nexus Fund II and RA Capital Nexus Fund IV GP, LLC is the general partner of the Nexus Fund IV. 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 each of the Fund, the Nexus Fund II and the Nexus Fund IV 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 II or the Nexus Fund IV. Each of the Fund, the Nexus Fund II and the Nexus Fund IV has delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in its portfolio, including the shares of the Issuer's common stock reported herein. Because each of the Fund, the Nexus Fund II and the Nexus Fund IV has divested itself of voting and investment power over the reported securities it holds and may not revoke that delegation on less than 61 days' notice, each of the Fund, the Nexus Fund II and the Nexus Fund IV disclaims beneficial ownership of the securities it holds for purposes of Section 13(d) of the Act and therefore disclaims 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 13G other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13G 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)
Percent of class:
Row 11 of each Reporting Person's cover page to this Schedule 13G sets forth the percentages of shares of common stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. Such percentage is based upon 61,727,211 shares of common stock outstanding as of August 3, 2026, as reported in the Issuer's Current Report on Form 8-K filed with the Securities and Exchange Commission (the "SEC") on August 3, 2026.
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
Row 5 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
(ii) Shared power to vote or to direct the vote:
Row 6 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
(iii) Sole power to dispose or to direct the disposition of:
Row 7 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
(iv) Shared power to dispose or to direct the disposition of:
Row 8 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
Item 5.
Ownership of 5 Percent or Less of a Class.
Not Applicable
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
Not Applicable
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
Not Applicable
Item 8.
Identification and Classification of Members of the Group.
Not Applicable
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.
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:
08/10/2026
Peter Kolchinsky
Signature:
/s/ Peter Kolchinsky
Name/Title:
Peter Kolchinsky
Date:
08/10/2026
Rajeev Shah
Signature:
/s/ Rajeev Shah
Name/Title:
Rajeev Shah
Date:
08/10/2026
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
