Atlas Venture Associates X, LLC

CIK 1742765 · last filed 2026-02-09

Atlas Venture Associates X, LLC is a corporate insider who has filed 7 SEC Form 4 insider transactions across 4 companies since 2018. The most recent filing, for GBIO, was dated Feb 9, 2026. Across all open-market trades the lifetime net is −$113.2M, making them a net seller over the disclosed history. Current disclosed insider exposure totals $826.1M across reported positions.

"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

$826.12M

Companies

4

Total Filings

7

Lifetime Open-Market Net

-$113.15M

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
Generation Bio Co. (GBIO) Delisted	10%+ Owner	0	$5.34	$0	-$14.05M	3	2026-02-09
IRON	10%+ Owner	2,235,846	$81.21	$181.57M	-$76.18M	2	2024-01-12
KYMR	10%+ Owner	5,879,854	$109.62	$644.55M	-$22.93M	1	2023-01-13
Tectonic Therapeutic, Inc. (AVRO) Delisted	10%+ Owner	396,373	$16.80	$6.66M	$0	1	2018-06-25

Recent Filings

7 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
2026-02-09	Generation Bio Co. (GBIO) Delisted	U	−4,967,676	$0	EDGAR
2024-01-12	IRON	Sell (S)	−300,000	-$19.20M	EDGAR
2023-09-18	IRON	Sell (S)	−1,072,347	-$56.98M	EDGAR
2023-01-13	KYMR	Sell (S)	−758,844	-$22.93M	EDGAR
2021-09-24	Generation Bio Co. (GBIO) Delisted	Sell (S)	−539,992	-$14.05M	EDGAR
2020-06-18	Generation Bio Co. (GBIO) Delisted	Conv (C)	+60,240,192	$0	EDGAR
2018-06-25	Tectonic Therapeutic, Inc. (AVRO) Delisted	Conv (C)	+14,269,434	$0	EDGAR

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.