SCHEDULE 13D/A Filed 2026-06-09 Event 2026-06-05 SEC 0001104659-26-071942 →

Fairmount Funds Management LLC → Jade Biosciences, Inc. JBIO

Stake: 19.99% Shares: 14,069,494 CUSIP: 008064206 Class: Common Stock, $0.0001 par value per share

Composite Decision Signal · WATCH (DEVELOPING SETUP) Conviction Score: 63/100 · Filer 90d Win Rate: 60% · Hist. 90d Edge: +13.7%

Filer track record (10 filings): 60% 90d win rate, +13.7% 90d edge
High conviction ownership stake (20.0%)
Material 8-K governance/transaction event (Item 5.02 / 1.01 / 2.01) within ±30d
Held by 1 tracked 13F institutional manager
8 NPORT-P mutual funds holding CUSIP
Elevated short days-to-cover (10.9 DTC)

Item 4 — Purpose of Transaction

Not extracted from this filing — typically because it's an amendment (13D/A) and Item 4 is unchanged from the parent filing. Read the raw SEC filing →

Cross-References

Insider Activity (last 365d)

1 transaction

1 buys · 0 sales · 0 awards/exercises

Issuer Cluster

6 13D/G filings on this issuer

5 other filings besides this one

Filer Track Record

22 filings by this filer

21 other filings in the data moat

Short Interest · settle 2026-10-15

DTC 10.87

11,210,801 shares short · -7.5% vs prior

Institutional Consensus · 2025-12-31

Held by elite portfolio managers

1 holder · $8.62M

Point72 Asset Mgmt

Post-Filing Returns · since 2026-06-05 on JBIO

+1 day

0.0%

+5 days

0.0%

+30 days

0.0%

+60 days

—

+90 days

—

+180 days

—

Anchor price 22.45 on closest trading day on/after 2026-06-05. Source: Yahoo Finance daily adj_close (split + dividend adjusted).

Form 4 Insider Transactions · last 365d

Date	Insider	Role	Type	Shares	Price	Value
2026-06-25	Eisner Mark	director	Award	47,675	$21.81	$1.04M

Other 13D/G Filings on Jade Biosciences, Inc.

Filed	Form	Filer	Stake	Shares
2025-04-30	SCHEDULE	Atlas Venture Fund XII, L.P.	20.00%	51,406	view →
2025-04-30	SCHEDULE	RA CAPITAL MANAGEMENT, L.P.	4.10%	1,324,954	view →
2024-06-20	SC	RA CAPITAL MANAGEMENT, L.P.	—	—	view →
2024-02-20	SC	Sofinnova Venture Partners X, L.P.	—	—	view →
2022-07-20	SC	Atlas Venture Fund XII, L.P.	—	—	view →

Other Filings by Fairmount Funds Management LLC

Filed	Form	Issuer	Stake	Shares
2026-10-15	SCHEDULE 13D	Alaunos Therapeutics, Inc.	19.99%	858,789	view →
2026-10-09	SCHEDULE 13D/A	SPYRE THERAPEUTICS, INC.	9.99%	9,354,200	view →
2026-09-11	SCHEDULE 13D	Korsana Biosciences, Inc.	19.99%	9,103,729	view →
2026-09-03	SCHEDULE 13D/A	Apogee Therapeutics, Inc.	—	0	view →
2026-07-20	SCHEDULE 13D/A	Crescent Biopharma, Inc.	—	6,593,385	view →
2026-07-01	SCHEDULE 13D/A	ORUKA THERAPEUTICS, INC. ORKA	19.50%	14,553,895	view →
2026-06-23	SCHEDULE 13D/A	SPYRE THERAPEUTICS, INC. SYRE	—	8,835,440	view →
2026-06-23	SCHEDULE 13D/A	Apogee Therapeutics, Inc. APGE	9.99%	6,713,519	view →
2026-05-13	SCHEDULE 13D/A	Viridian Therapeutics, Inc.\DE VRDN	—	17,201,800	view →
2026-01-22	SCHEDULE	Cogent Biosciences, Inc. COGT	9.90%	16,261,918	view →
2026-01-22	SCHEDULE	Apogee Therapeutics, Inc. APGE	9.99%	6,047,027	view →
2025-10-14	SCHEDULE	Apogee Therapeutics, Inc. APGE	9.99%	5,776,881	view →
2025-09-15	SCHEDULE	Dianthus Therapeutics, Inc. /DE/ DNTH	9.90%	4,052,052	view →
2025-03-10	SCHEDULE	Oruka Therapeutics, Inc. ORKA	19.99%	8,511,824	view →
2024-04-01	SC	Cogent Biosciences, Inc. COGT	—	—	view →
2024-04-01	SC	Dianthus Therapeutics, Inc. /DE/ DNTH	—	—	view →
2024-04-01	SC	Viridian Therapeutics, Inc.\DE VRDN	—	—	view →
2024-04-01	SC	Apogee Therapeutics, Inc. APGE	—	—	view →
2023-12-11	SC	Spyre Therapeutics, Inc. SYRE	—	—	view →
2023-06-13	SC	Cogent Biosciences, Inc. COGT	—	—	view →

Showing 20 of 21

Want this depth on every filing the moment it hits SEC EDGAR?

Free $0 (48h-delayed alerts) · Individual $49/mo (real-time) · Team & API $199/mo · Enterprise.

See pricing →