Comparable stake leader
SymBiosis Capital Partners, LLC
SEC ownership of Generation Bio Co.
Top holders, 13D/G large-stake signals, insider positions, and transaction flow tied to CIK 0001733294.
Disclosed value leader
SymBiosis Capital Partners, LLC
Comparable rows
6/25
Latest evidence
31 Mar 2026
- SEC evidence covered
- 13D/G, 13F, and 3/4/5
- Largest SEC-reported holder
- SymBiosis Capital Partners, LLC
- Latest 13D/G holder
- SymBiosis Capital Partners, LLC
- Latest parsed evidence date
- 31 Mar 2026
- CIK
- 0001733294
- Location
- Cambridge, MA
Ownership snapshot
2 signals
Issuer
2 identity fields
Ownership snapshot
Top shareholders of Generation Bio Co. (13F + 13D/G + 3/4/5)
Grouped by holder across the latest SEC ownership disclosures. Start with comparable ownership when available, then verify the linked 13F, 13D/G, or 3/4/5 evidence.
Comparable stake leader
SymBiosis Capital Partner...
Disclosed value leader
SymBiosis Capital Partner...
Comparable rows
6/25
Latest evidence
31 Mar 2026
13D/G
13F
3/4/5
Lead comparable stake: 6.3%
19 rows are not safely comparable across share classes.
13D/G row: SymBiosis Capital Partners, LLC
Showing 1-8 of 25 holder rows.
Quick read
SymBiosis Capital Partners, LLC leads the comparable SEC ownership view at 6.3%.
6 of 25 rows have a safely comparable ownership percentage. Use this as a filing-backed starting point, then open the detailed table for source links, reporting role, position value, share count, and filing date.
Comparable ownership
Top 5
SymBiosis Capital Partners, LLC
6.3%
RENAISSANCE TECHNOLOGIES LLC
4.3%
FMR LLC
3.5%
PRICE T ROWE ASSOCIATES INC /MD/
3.1%
BlackRock, Inc.
1.7%
Ownership % is shown only when SEC disclosures are safely comparable across share classes.
Detailed SEC evidence table Showing 1-8 of 25 holder rows
| Holder | Evidence | Ownership % | Position | 12M Net Δ | As of |
|---|---|---|---|---|---|
| SymBiosis Capital Partners, LLC |
13D/G
|
6.3%
|
$2,582,018
421,926 shares
|
$0 | 30 Sep 2025 |
| RENAISSANCE TECHNOLOGIES LLC |
13D/G
|
4.3%
|
$1,576,125
287,614 shares
|
-$310,437 | 31 Dec 2025 |
| FMR LLC |
13D/G
|
3.5%
|
$750,600
2,345,624 shares
|
-$729,735 | 30 Jun 2025 |
| PRICE T ROWE ASSOCIATES INC /MD/ |
13D/G
T. Rowe Price Associates, Inc.
|
3.1%
|
$1,148,833
209,641 shares
|
-$2,011,971 | 31 Dec 2025 |
| BlackRock, Inc. |
13D/G
|
1.7%
|
$414,737
1,152,047 shares
|
$0 | 30 Jun 2025 |
| Accent Capital Management, LLC |
13F
Company
|
0%
|
$53,260
61 shares
|
— | 31 Mar 2026 |
| ATLAS VENTURE ASSOCIATES X, L.P. |
3/4/5
10%+ Owner
|
—
class O/S missing
|
$1,161
608 shares
|
— | 27 Sep 2021 |
| Matthew Stanton |
3/4/5
CHIEF SCIENTIFIC OFFICER
|
—
mixed-class rows
|
$1,372,339
423,028 shares
mixed-class rows
|
— | 10 Jan 2025 |
How to read this table
Rows are grouped by holder and ranked first by SEC-reported ownership % when it is safely comparable, then by disclosed holdings value. — indicates unavailable or non-comparable values; "mixed-class rows" means the latest filing spans non-comparable classes.
Forms 3/4/5 flow
Insider trading overview
Insider buy and sell flow is broadly balanced over the last 12 months. No Buy or Sell transactions have been reported since 03 Jun 2025.
Buys
$0
Insiders: 0
Sells
$0
Insiders: 0
Net
$0
Shares: 0
Window
Last 12 months
4 rolling buckets
Buy value
Sell value
Shares: 0
Shares: 0
| Window (months) | Buy shares | Sell shares | Buy value | Sell value | Net value |
|---|---|---|---|---|---|
| 0-3 | 0 | 0 | $0 | $0 | $0 |
| 3-6 | 0 | 0 | $0 | $0 | $0 |
| 6-9 | 0 | 0 | $0 | $0 | $0 |
| 9-12 | 0 | 0 | $0 | $0 | $0 |
Reporting owners
Insider holders from Forms 3/4/5
Showing 1-20 of 20 reporting-owner rows connected to Generation Bio Co.. Open a relationship link for the CIK-to-CIK filing trail.
Rows
20
Largest Forms 3/4/5 holder
Matthew Stanton
Net 12M change
$0
Latest report
09 Feb 2026
Recent insider transactions for Generation Bio Co.
Showing up to 300 recent insider transactions from the last 12 months.
| Insider | Symbol | Class | Transaction | % | SEC-reported value | SEC-reported price | Shares | Shares owned | Date | Ownership |
|---|---|---|---|---|---|---|---|---|---|---|
| Atlas Venture Fund X, L.P. | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -116,753 | 0 | 09 Feb 2026 | See footnote | ||
| Atlas Venture Fund X, L.P. | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -711,193 | 0 | 09 Feb 2026 | Direct | ||
| Catherine Stehman-Breen | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -4,752 | 0 | 09 Feb 2026 | Direct | ||
| Catherine Stehman-Breen | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -20,120 | 0 | 09 Feb 2026 | Direct | ||
| Charles A. Rowland Jr. | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -53,475 | 0 | 09 Feb 2026 | Direct | ||
| Charles A. Rowland Jr. | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -24,366 | 0 | 09 Feb 2026 | Direct | ||
| Jason P. Rhodes | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -827,946 | 0 | 09 Feb 2026 | See Footnote | ||
| Jason P. Rhodes | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -20,120 | 0 | 09 Feb 2026 | Direct | ||
| Anthony G. Quinn | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -7,283 | 0 | 09 Feb 2026 | By Quinn Family Irrevocable Trust of 2021 | ||
| Anthony G. Quinn | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -29,928 | 0 | 09 Feb 2026 | Direct | ||
| Anthony G. Quinn | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -20,120 | 0 | 09 Feb 2026 | Direct | ||
| Donald William Nicholson | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -21,357 | 0 | 09 Feb 2026 | Direct | ||
| Donald William Nicholson | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -20,120 | 0 | 09 Feb 2026 | Direct | ||
| Geoff Mcdonough | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -27,500 | 0 | 09 Feb 2026 | By 2020 Trust | ||
| Geoff Mcdonough | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -22,646 | 0 | 09 Feb 2026 | By 2018 Trust | ||
| Geoff Mcdonough | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -138,492 | 0 | 09 Feb 2026 | Direct | ||
| Geoff Mcdonough | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -264,213 | 0 | 09 Feb 2026 | Direct | ||
| Jeffrey M. Jonas | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -24,366 | 0 | 09 Feb 2026 | Direct | ||
| Yalonda Howze | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -3,759 | 0 | 09 Feb 2026 | Direct | ||
| Yalonda Howze | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -55,325 | 0 | 09 Feb 2026 | Direct | ||
| Ronald Harold Wilfred Cooper | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -950 | 0 | 09 Feb 2026 | Direct | ||
| Ronald Harold Wilfred Cooper | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -16,420 | 0 | 09 Feb 2026 | Direct | ||
| Kevin John Conway | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -2,072 | 0 | 09 Feb 2026 | Direct | ||
| Kevin John Conway | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -56,045 | 0 | 09 Feb 2026 | Direct | ||
| Gustav Christensen | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -13,142 | 0 | 09 Feb 2026 | Direct | ||
| Gustav Christensen | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -20,120 | 0 | 09 Feb 2026 | Direct | ||
| Dannielle Appelhans | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -736 | 0 | 09 Feb 2026 | By Spouse | ||
| Dannielle Appelhans | GBIO | Common Stock | Disposition pursuant to a tender of shares in a change of control transaction | -100% | -1,263 | 0 | 09 Feb 2026 | Direct | ||
| Dannielle Appelhans | GBIO | Stock Option (right to buy) | Disposed to Issuer | -100% | -15,340 | 0 | 09 Feb 2026 | Direct | ||
| Kevin John Conway | GBIO | Common Stock | Tax liability | -3.36% | -72 | 2,072 | 02 Feb 2026 | Direct | ||
| Kevin John Conway | GBIO | Common Stock | Options Exercise | 12.3% | 235 | 2,144 | 02 Feb 2026 | Direct | ||
| Kevin John Conway | GBIO | Restricted Stock Units | Options Exercise | -100% | -235 | 0 | 02 Feb 2026 | Direct | ||
| Yalonda Howze | GBIO | Common Stock | Tax liability | -11.6% | -495 | 3,759 | 02 Feb 2026 | Direct | ||
| Yalonda Howze | GBIO | Common Stock | Options Exercise | 64.8% | 1,673 | 4,254 | 02 Feb 2026 | Direct | ||
| Yalonda Howze | GBIO | Restricted Stock Units | Options Exercise | -100% | -1,673 | 0 | 02 Feb 2026 | Direct | ||
| Geoff Mcdonough | GBIO | Common Stock | Tax liability | -0.4% | -550 | 138,492 | 02 Feb 2026 | Direct | ||
| Geoff Mcdonough | GBIO | Common Stock | Options Exercise | 1.15% | 1,582 | 139,042 | 02 Feb 2026 | Direct | ||
| Geoff Mcdonough | GBIO | Restricted Stock Units | Options Exercise | -100% | -1,582 | 0 | 02 Feb 2026 | Direct | ||
| Kevin John Conway | GBIO | Common Stock | Tax liability | -0.88% | -17 | 1,909 | 15 Jan 2026 | Direct | ||
| Kevin John Conway | GBIO | Common Stock | Options Exercise | 3.16% | 59 | 1,926 | 15 Jan 2026 | Direct | ||
| Kevin John Conway | GBIO | Restricted Stock Units | Options Exercise | -20.1% | -59 | 235 | 15 Jan 2026 | Direct | ||
| Geoff Mcdonough | GBIO | Common Stock | Tax liability | -0.1% | -137 | 137,460 | 15 Jan 2026 | Direct | ||
| Geoff Mcdonough | GBIO | Common Stock | Options Exercise | 0.29% | 395 | 137,597 | 15 Jan 2026 | Direct | ||
| Geoff Mcdonough | GBIO | Restricted Stock Units | Options Exercise | 33.3% | 395 | 1,582 | 15 Jan 2026 | Direct | ||
| Yalonda Howze | GBIO | Common Stock | Tax liability | -3.69% | -99 | 2,581 | 15 Jan 2026 | Direct | ||
| Yalonda Howze | GBIO | Common Stock | Options Exercise | 14.3% | 335 | 2,680 | 15 Jan 2026 | Direct | ||
| Yalonda Howze | GBIO | Restricted Stock Units | Options Exercise | -16.7% | -335 | 1,673 | 15 Jan 2026 | Direct | ||
| Geoff Mcdonough | GBIO | Common Stock | Tax liability | -0.21% | -293 | 137,202 | 31 Oct 2025 | Direct | ||
| Geoff Mcdonough | GBIO | Common Stock | Options Exercise | 0.48% | 659 | 137,495 | 31 Oct 2025 | Direct | ||
| Geoff Mcdonough | GBIO | Restricted Stock Units | Options Exercise | -25% | -659 | 1,977 | 31 Oct 2025 | Direct |
* marks a reported price that did not pass the local price check.