Atlas Venture Opportunity Fund II, L.P.

CIK 1885327 · last filed 2025-02-10

Atlas Venture Opportunity Fund II, L.P. is a corporate insider who has filed 54 SEC Form 4 insider transactions across 2 companies since 2024. The most recent filing, for KRRO, was dated Sep 14, 2026. Across all open-market trades the lifetime net is −$95.6M, making them a net seller over the disclosed history. Current disclosed insider exposure totals $134.2M across reported positions. The firm reports its address in Cambridge, MA. 11 SEC filings were submitted jointly with Atlas Venture Associates Opportunity II, LLC.

"Disclosed insider exposure" sums this person's most-recently-reported share counts across each company they're an insider in, multiplied by the current underlying price. It is not net worth — it misses retail holdings, private investments, real estate, index funds, and any company where the person isn't an SEC-reporting insider. For informational purposes only.

Disclosed Exposure

$134.20M

Companies

Total Filings

Lifetime Open-Market Net

-$95.58M

Charts

Trading activity, where the exposure sits, and each trade against the stock price.

Filer Profile

Reported Address

300 TECHNOLOGY SQUARE
8TH FLOOR
CAMBRIDGE, MA 02139

Phone

(857) 201-2700

State of Incorporation

Related Filers

Atlas Venture Associates Opportunity II, LLC — 11 joint filings, latest 2025-02-10

Atlas Venture Associates Opportunity I, L.P. — 7 joint filings, latest 2024-03-27

Atlas Venture Associates Opportunity I, LLC — 7 joint filings, latest 2024-03-27

Atlas Venture Associates XI, L.P. — 7 joint filings, latest 2025-02-10

Atlas Venture Associates XI, LLC — 7 joint filings, latest 2025-02-10

Atlas Venture Fund XI, L.P. — 7 joint filings, latest 2025-02-10

Atlas Venture Opportunity Fund I, L.P. — 7 joint filings, latest 2024-03-27

ATLAS VENTURE ASSOCIATES X, L.P. — 2 joint filings, latest 2024-03-27

Profile details as reported on the filer's SEC submissions — for individual insiders the address is often in care of the issuer. Related filers are identified from jointly filed SEC submissions and shared reported addresses. View filings on SEC EDGAR.

Holdings By Company

Latest on-record share count from this person's most recent non-derivative Form 4 transaction in each company. Disclosed exposure = shares × current underlying price.

Symbol	Role	Shares	Price	Disclosed Exposure	Lifetime OM Net	Filings	Latest Filed
SION	10%+ Owner	3,694,020	$4.81	$17.77M	$6.48M	1	2025-02-10
DYN	10%+ Owner	7,587,471	$15.35	$116.43M	-$102.06M	1	2024-02-23

Recent Filings

54 filings

Insider activity across all companies, newest first. Form 4 rows are post-trade confirmations (buys, sells, grants, exercises). Notice (144) rows are pre-trade notices of intent to sell restricted or control stock under Rule 144 — they may not all execute. Compare adjacent dates to see which notices became actual sales.

Filed	Symbol	Action	Net Shares	Net $	Link
2026-09-14	KRRO	Notice (144)	−6,602	-$91.2K	EDGAR
2026-09-11	KRRO	Notice (144)	−1,750	-$22.9K	EDGAR
2026-09-04	IRON	Notice (144)	−759	-$60.2K	EDGAR
2026-09-03	IRON	Notice (144)	−2,339	-$187.2K	EDGAR
2026-08-26	KRRO	Notice (144)	−51	-$700	EDGAR
2026-08-19	KRRO	Notice (144)	−4,884	-$64.6K	EDGAR
2026-08-14	DYN	Notice (144)	−478,377	-$12.42M	EDGAR
2026-08-13	DYN	Notice (144)	−94,415	-$2.47M	EDGAR
2026-08-11	KRRO	Notice (144)	−368	-$5.0K	EDGAR
2026-07-07	DYN	Notice (144)	−77,387	-$1.77M	EDGAR

Showing 1–10 of 54

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Form 4 codes: P = open-market purchase · S = open-market sale · A = grant/award · M = option exercise · F = tax withholding at vest · G = bona-fide gift · D = disposition to issuer · J = other (see filing footnote). Only P / S codes carry directional signal.
Notice (144 / 144/A): Form 144 is a notice of intent to sell restricted/control stock under Rule 144, filed before the sale; 144/A is an amendment. Many notices are pre-scheduled under Rule 10b5-1 plans. A Form 4 with code S typically follows within a few days when the planned sale executes; missing follow-up Form 4s suggest the notice was cancelled or modified.