Atlas Venture Fund X, L.P.
CIK 1628098 · last filed 2024-01-25
Atlas Venture Fund X, L.P. is a corporate insider who has filed 67 SEC Form 4 insider transactions across 6 companies since 2018. The most recent filing, for IRON, was dated Sep 4, 2026. Across all open-market trades the lifetime net is −$46.3M, making them a net seller over the disclosed history. Current disclosed insider exposure totals $765.8M across reported positions. The firm reports its address in Cambridge, MA. 29 SEC filings were submitted jointly with ATLAS VENTURE ASSOCIATES X, L.P.
"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.
Charts
Trading activity, where the exposure sits, and each trade against the stock price.
Filer Profile
10TH FLOOR
CAMBRIDGE, MA 02139
Holdings By Company
| Symbol | Role | Shares | Price | Disclosed Exposure | Lifetime OM Net | Filings | Latest Filed |
|---|---|---|---|---|---|---|---|
| IRON | 10%+ Owner | 2,105,846 | $63.49 | $133.70M | -$91.33M | 1 | 2024-01-25 |
| Generation Bio Co. (GBIO) Delisted | 10%+ Owner | 827,888 | $5.34 | $4.42M | $0 | 4 | 2021-09-21 |
| KYMR | 10%+ Owner | 5,763,012 | $104.13 | $600.10M | $0 | 2 | 2021-05-18 |
| Dianthus Therapeutics, Inc. /DE/ (MGTA) Delisted | 10%+ Owner | 196,775 | $11.19 | $2.20M | $0 | 2 | 2021-02-16 |
| REPL | 10%+ Owner | 2,486,296 | $12.86 | $31.97M | $0 | 4 | 2020-09-17 |
| Tectonic Therapeutic, Inc. (AVRO) Delisted | 10%+ Owner | 396,373 | $16.80 | $6.66M | $45.00M | 2 | 2019-07-29 |
Recent Filings
67 filings| Filed | Symbol | Action | Net Shares | Net $ | Link |
|---|---|---|---|---|---|
| 2026-09-04 | IRON | Notice (144) | −2,212 | -$175.6K | EDGAR |
| 2026-09-03 | IRON | Notice (144) | −6,822 | -$546.1K | EDGAR |
| 2026-06-29 | KYMR | Notice (144) | −66,177 | -$7.16M | EDGAR |
| 2026-06-26 | KYMR | Notice (144) | −410,427 | -$47.80M | EDGAR |
| 2026-06-25 | KYMR | Notice (144) | −480,992 | -$48.04M | EDGAR |
| 2026-06-24 | KYMR | Notice (144) | −118,178 | -$11.61M | EDGAR |
| 2026-06-23 | KYMR | Notice (144) | −1,235 | -$122.8K | EDGAR |
| 2026-06-22 | KYMR | Notice (144) | −243,976 | -$22.06M | EDGAR |
| 2026-06-18 | KYMR | Notice (144) | −100,928 | -$9.07M | EDGAR |
| 2026-06-17 | KYMR | Notice (144) | −92,169 | -$8.06M | EDGAR |
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.