Fairmount Funds Management LLC - 09 Jun 2026 Form 4 Insider Report for Jade Biosciences, Inc. (JBIO)

Reporting relationship: Director, 10%+ Owner
Issuer ticker: JBIO
Reported as of: 09 Jun 2026
Net transaction value: $0
SEC form: 4
Accepted by SEC: 11 Jun 2026, 16:37:08 UTC
Prior SEC filing: 03 Jun 2026
Next SEC filing: 23 Jun 2026
Source filing: View source filing
Reporting owner signature: /s/ Tomas Kiselak, Managing Member of Fairmount Funds Management LLC

Key filing fact

Fairmount Funds Management LLC filed Form 4 for Jade Biosciences, Inc. (JBIO) on 11 Jun 2026.

Key facts

This page summarizes Fairmount Funds Management LLC's Form 4 filing for Jade Biosciences, Inc. (JBIO).
1 reported transaction and 5 derivative rows are listed below.
Accepted by SEC: 11 Jun 2026, 16:37.

Change

Previous filing in this sequence was filed on 03 Jun 2026.
Current net transaction value: $0.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (5)

CIK 0001802528 Primary reporting owner

Fairmount Funds Management LLC

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Tomas Kiselak, Managing Member of Fairmount Funds Management LLC
Signature date: 11 Jun 2026

CIK 0001769651

Fairmount Healthcare Fund II L.P.

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Fund II L.P.
Signature date: 11 Jun 2026

CIK 0002042283

Fairmount Healthcare Co-Invest IV L.P.

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Co-Invest IV L.P.
Signature date: 11 Jun 2026

CIK 0001830177

Kiselak Tomas

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Tomas Kiselak
Signature date: 11 Jun 2026

CIK 0001663607

Harwin Peter Evan

Relationship: Director, 10%+ Owner
Address: 200 BARR HARBOR DRIVE, SUITE 400, WEST CONSHOHOCKEN
Signature: /s/ Peter Harwin
Signature date: 11 Jun 2026

Reported derivative securities

Options, warrants, convertible securities, or similar derivative positions disclosed in the filing.

JBIO transaction Derivative

Stock Option (Right to Buy)

Award

Transaction value
Shares: +34,843
Change %
Price: $0.000000^*
Shares after: 34,843
Date: 09 Jun 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 34,843
Exercise price: $15.22
Footnotes: F1, F2

JBIO transaction Derivative

Stock Option (Right to Buy)

Award

Transaction value
Shares: +34,843
Change %
Price: $0.000000^*
Shares after: 34,843
Date: 09 Jun 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 34,843
Exercise price: $15.22
Footnotes: F1, F2

JBIO transaction Derivative

Stock Option (Right to Buy)

Award

Transaction value
Shares: +34,843
Change %
Price: $0.000000^*
Shares after: 34,843
Date: 09 Jun 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 34,843
Exercise price: $15.22
Footnotes: F1, F2

JBIO transaction Derivative

Stock Option (Right to Buy)

Award

Transaction value
Shares: +34,843
Change %
Price: $0.000000^*
Shares after: 34,843
Date: 09 Jun 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 34,843
Exercise price: $15.22
Footnotes: F1, F2

JBIO transaction Derivative

Stock Option (Right to Buy)

Award

Transaction value
Shares: +34,843
Change %
Price: $0.000000^*
Shares after: 34,843
Date: 09 Jun 2026
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 34,843
Exercise price: $15.22
Footnotes: F1, F2

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Explanation of responses 2 footnotes

Footnote F1

This option represents a right to purchase shares of the Issuer's common stock, which vests in full on the earlier of (i) June 9, 2027 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to Tomas Kiselak's continued service to the Issuer.

Footnote F2

Fairmount Funds Management LLC ("Fairmount") is the investment manager for Fairmount Healthcare Fund II LP ("Fund II") and Fairmount Healthcare Co-Invest IV L.P. ("Co-Invest"). Peter Harwin and Tomas Kiselak are the managers of Fairmount. Under Mr. Kiselak's arrangement with Fairmount, Mr. Kiselak holds the option for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). Mr. Kiselak is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

SEC remarks

Fairmount, Fairmount Healthcare Fund II L.P. and Fairmount Healthcare Co-Invest IV L.P. may each be deemed a director by deputization of the 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.