[Form 4] Jade Biosciences, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Insiders and affiliated funds purchased equity in Jade Biosciences (JBIO). On 10/06/2025, affiliated investors acquired 1,333,126 shares of common stock at $9.14 per share and received 855,047 pre-funded warrants exercisable into the same number of shares (exercise price $0.0001); the underlying common shares for the warrants are tied to an effective price of $9.1399. After the transactions, the reported beneficial ownership stakes include 1,897,677 shares attributed indirectly to Fairmount Healthcare Fund II L.P. and 2,655,817 shares indirectly attributed to Fairmount Healthcare Co-Invest IV L.P.

The filing notes the securities were purchased in a private placement and relies on Rule 16b-3(d)(1) exemption. Fairmount Funds Management LLC is the manager for the two funds, and Tomas Kiselak and Peter Harwin are identified as managers; they disclaim beneficial ownership except for pecuniary interests. The pre-funded warrants have no expiration and include a 9.99% beneficial ownership cap on exercise.

Positive

• Material equity infusion: Acquisition of 1,333,126 shares and 855,047 pre-funded warrants provides capital via private placement at $9.14 (or equivalent).
• Pre-funded warrants are exercisable with no expiration, allowing flexible conversion timing for holders.

Negative

• Director-affiliate overlap: A board member (Tomas Kiselak) is also a managing member of the reporting manager, which could raise governance scrutiny.
• Exercise cap: Pre-funded warrants include a 9.99% ownership limit that may delay or restrict conversion timing and affect dilution expectations.

Insights

Investor Relations Analyst

Significant insider-aligned private placement increases affiliated ownership.

The transaction increases the affiliated funds' indirect stake by several million shares via a mix of common stock and pre-funded warrants, resulting in reported indirect holdings of 1,897,677 and 2,655,817 shares respectively. The use of pre-funded warrants allows immediate economic exposure while limiting voting dilution until exercise.

Risks include the 9.99% ownership cap on warrant exercise which can affect timing of conversion. Watch for any future exercises or resale activity in the weeks to months after 10/06/2025.

Corporate Governance Specialist

Manager and director overlap creates potential governance attention.

Fairmount Funds Management LLC manages the two reporting funds and two individuals—Tomas Kiselak and Peter Harwin—are identified as managers; Mr. Kiselak also serves on the issuer's board. The filing disclaims beneficial ownership except for pecuniary interests, which is standard language but highlights a director-affiliate link.

Investors may monitor related-party disclosures and any board actions where these interests intersect, especially in the near term after the private placement closing on 10/06/2025.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Fairmount Funds Management LLC

(Last) (First) (Middle)

200 BARR HARBOR DRIVE

SUITE 400

(Street)

WEST CONSHOHOCKEN PA 19428

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Jade Biosciences, Inc. [ JBIO ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

3. Date of Earliest Transaction (Month/Day/Year)
10/06/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

	Form filed by One Reporting Person
X	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	10/06/2025		A(1)		1,333,126	A	$9.14	1,897,677	I	By Fairmount Healthcare Fund II L.P.(2)
Common Stock								2,655,817	I	By Fairmount Healthcare Co-Invest IV L.P.(2)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Pre-Funded Warrant (Right to Buy)	$0.0001	10/06/2025		A(1)		855,047		(3)	(3)	Common Stock	855,047	$9.1399	855,047	I	By Fairmount Healthcare Fund II L.P.(2)

1. Name and Address of Reporting Person^*

Fairmount Funds Management LLC

(Last) (First) (Middle)

200 BARR HARBOR DRIVE

SUITE 400

(Street)

WEST CONSHOHOCKEN PA 19428

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

Fairmount Healthcare Fund II L.P.

(Last) (First) (Middle)

200 BARR HARBOR DRIVE

SUITE 400

(Street)

WEST CONSHOHOCKEN PA 19428

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

Fairmount Healthcare Co-Invest IV L.P.

(Last) (First) (Middle)

200 BARR HARBOR DRIVE

SUITE 400

(Street)

WEST CONSHOHOCKEN PA 19428

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

Kiselak Tomas

(Last) (First) (Middle)

200 BARR HARBOR DRIVE

SUITE 400

(Street)

WEST CONSHOHOCKEN PA 19428

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

1. Name and Address of Reporting Person^*

Harwin Peter Evan

(Last) (First) (Middle)

200 BARR HARBOR DRIVE

SUITE 400

(Street)

WEST CONSHOHOCKEN PA 19428

(City) (State) (Zip)

Relationship of Reporting Person(s) to Issuer

X	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

Explanation of Responses:

1. The shares of Common Stock and Pre-Funded Warrants were purchased from the Issuer in a private placement, which transaction is exempt from Section 16(b) in accordance with Rule 16b-3(d)(1) promulgated under the Securities Exchange Act of 1934, as amended.

2. Fairmount Funds Management LLC ("Fairmount") is the investment manager for Fairmount Healthcare Fund II L.P. and Fairmount Healthcare Co-Invest IV L.P. The managers of Fairmount are Peter Harwin and Tomas Kiselak. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

3. The Pre-Funded Warrants have no expiration date and are exercisable at any time after the date of issuance. A holder of Pre-Funded Warrants may not exercise the Pre-Funded Warrant if the holder, together with its affiliates, would beneficially own more than 9.99% of the number of outstanding shares of common stock of the Issuer immediately after giving effect to such exercise.

Remarks:

Fairmount may be deemed a director by deputization of Issuer by virtue of the fact that Tomas Kiselak serves on the board of directors of the Issuer and is also a Managing Member of Fairmount.

	/s/ Tomas Kiselak, Managing Member of Fairmount Funds Management LLC	10/08/2025
	/s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Fund II, L.P.	10/08/2025
	/s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Co-Invest IV, L.P.	10/08/2025
	/s/ Tomas Kiselak	10/08/2025
	/s/ Peter Harwin	10/08/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
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FAQ

What did Jade Biosciences insiders buy on 10/06/2025 (JBIO)?

Affiliated funds purchased 1,333,126 shares of common stock at $9.14 and received 855,047 pre-funded warrants exercisable into common stock; the transaction closed on 10/06/2025.

Who filed the Form 4 for JBIO and what is their relationship to the company?

The filing lists Fairmount Funds Management LLC, Fairmount Healthcare Fund II L.P., Fairmount Healthcare Co-Invest IV L.P., and individuals Tomas Kiselak and Peter Harwin; Mr. Kiselak serves on the issuer's board.

What are the terms of the pre-funded warrants reported for JBIO?

The pre-funded warrants were issued with an exercise price of $0.0001, have no expiration date, and include a limit that prevents exercise if the holder would own more than 9.99% after conversion.

Was the transaction a public offering or private placement for JBIO?

The shares and pre-funded warrants were purchased in a private placement, and the filing cites the Rule 16b-3(d)(1) exemption.

How many shares are reported beneficially owned after the transaction?

Reported indirect beneficial ownership includes 1,897,677 shares for Fairmount Healthcare Fund II L.P. and 2,655,817 shares for Fairmount Healthcare Co-Invest IV L.P.