As of November 6, 2026, 4 holders' latest Schedule 13D or 13G filings report owning 5% or more of AdvanSix Inc. The largest reported stake is BlackRock, Inc.'s, at 7.1%. 10 filings are on record since October 30, 2025 (Schedule 13G/A, April 24, 2026).
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Key facts
- · Reporting person: American Century Investment Management, Inc. · Sole voting: 1,363,346 · Shared voting: 0 · Sole dispositive: 1,363,346 · Shared dispositive: 0 · SCHEDULE 13G, 2026-08-14
- · Reporting person: Dimensional Fund Advisors LP · Sole voting: 1,380,649 · Shared voting: 0 · Sole dispositive: 1,407,349 · Shared dispositive: 0 · SCHEDULE 13G, 2026-07-14
- · Reporting person: CastleKnight Master Fund LP · Sole voting: 0 · Shared voting: 1,666,382 · Sole dispositive: 0 · Shared dispositive: 1,666,382 · SCHEDULE 13G, 2026-05-14
- · Reporting person: BlackRock, Inc. · Sole voting: 1,891,978 · Shared voting: 0 · Sole dispositive: 1,919,001 · Shared dispositive: 0 · SCHEDULE 13G/A, 2026-04-24
- · Holder: The Vanguard Group · Percent: 0% · SCHEDULE 13G/A
AdvanSix Inc. has 10 Schedule 13D or 13G filings on record since 2025-10-30. 4 holders' latest filing reports 5% or more of common stock. Each figure below is the holder's own, as filed, with the filing linked.
Holders
| Holder | Percent | Shares | Latest | Event date |
|---|---|---|---|---|
| BlackRock, Inc. | 7.1% | 1,919,001 | SCHEDULE 13G/A, 2026-04-24 | 2026-03-31 |
| CastleKnight Master Fund LP | 6.2% | 1,666,382 | SCHEDULE 13G, 2026-05-14 | 2026-05-07 |
| Dimensional Fund Advisors LP | 5.2% | 1,407,349 | SCHEDULE 13G, 2026-07-14 | 2026-06-30 |
| American Century Investment Management, Inc. | 5.1% | 1,363,346 | SCHEDULE 13G, 2026-08-14 | 2026-06-30 |
| Victory Capital Management, Inc. | 0.51% | 137,620 | SCHEDULE 13G/A, 2026-02-11 | 2025-09-30 |
| The Vanguard Group | 0% | 0 | SCHEDULE 13G/A, 2026-03-26 | 2026-03-13 |
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More on AdvanSix Inc. and the records around it.
AdvanSix Inc. elsewhere on the record
- Leadership changes Apr 2026
- Who owns it
Companies that share a holder
- CastleKnight Master Fund LP also filed stake reports on 17 other companies: Suja Life, Inc. (Aug 2026), Advantage Solutions Inc. (Aug 2026), HAIN CELESTIAL GROUP INC (Aug 2026)
- Victory Capital Management, Inc. also filed stake reports on 41 other companies: Angel Oak Mortgage REIT, Inc. (Nov 2026), Bowhead Specialty Holdings Inc. (Jul 2026), Dole plc (Jul 2026)
- American Century Investment Management, Inc. also filed stake reports on 83 other companies: Visteon Corporation (Oct 2026), MarineMax, Inc. (Sep 2026), Allegiant Travel Company (Aug 2026)
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Voting and dispositive power, as filed
| Reporting person | Sole voting | Shared voting | Sole dispositive | Shared dispositive | Filing |
|---|---|---|---|---|---|
| BlackRock, Inc. | 1,891,978 | 0 | 1,919,001 | 0 | SCHEDULE 13G/A, 2026-04-24 |
| CastleKnight Master Fund LP | 0 | 1,666,382 | 0 | 1,666,382 | SCHEDULE 13G, 2026-05-14 |
| CastleKnight Fund GP LLC | 0 | 1,666,382 | 0 | 1,666,382 | SCHEDULE 13G, 2026-05-14 |
| CastleKnight Management LP | 0 | 1,666,382 | 0 | 1,666,382 | SCHEDULE 13G, 2026-05-14 |
| CastleKnight Management GP LLC | 0 | 1,666,382 | 0 | 1,666,382 | SCHEDULE 13G, 2026-05-14 |
| Weitman Capital LLC | 0 | 1,666,382 | 0 | 1,666,382 | SCHEDULE 13G, 2026-05-14 |
| Aaron Weitman | 0 | 1,666,382 | 0 | 1,666,382 | SCHEDULE 13G, 2026-05-14 |
| Dimensional Fund Advisors LP | 1,380,649 | 0 | 1,407,349 | 0 | SCHEDULE 13G, 2026-07-14 |
| American Century Investment Management, Inc. | 1,363,346 | 0 | 1,363,346 | 0 | SCHEDULE 13G, 2026-08-14 |
| American Century Companies, Inc. | 1,363,346 | 0 | 1,363,346 | 0 | SCHEDULE 13G, 2026-08-14 |
| Stowers Institute for Medical Research | 1,363,346 | 0 | 1,363,346 | 0 | SCHEDULE 13G, 2026-08-14 |
The latest filing identifies AdvanSix Inc. by CUSIP 00773T101 and gives its principal executive office as 300 Kimball Drive, Suite 101, Parsippany, NJ 07054 (SCHEDULE 13G, 2026-08-14).
Timeline
| Filed | Holder | Percent | Filing |
|---|---|---|---|
| 2025-10-30 | Victory Capital Management, Inc. | 8.12% | SCHEDULE 13G/A |
| 2026-01-08 | BlackRock, Inc. | 11.9% | SCHEDULE 13G/A |
| 2026-01-21 | Dimensional Fund Advisors LP | 4.8% | SCHEDULE 13G/A |
| 2026-01-30 | The Vanguard Group | 6.35% | SCHEDULE 13G/A |
| 2026-02-11 | Victory Capital Management, Inc. | 0.51% | SCHEDULE 13G/A |
| 2026-03-26 | The Vanguard Group | 0% | SCHEDULE 13G/A |
| 2026-04-24 | BlackRock, Inc. | 7.1% | SCHEDULE 13G/A |
| 2026-05-14 | CastleKnight Master Fund LP | 6.2% | SCHEDULE 13G |
| 2026-07-14 | Dimensional Fund Advisors LP | 5.2% | SCHEDULE 13G |
| 2026-08-14 | American Century Investment Management, Inc. | 5.1% | SCHEDULE 13G |
Questions about who owns AdvanSix Inc.
Who owns AdvanSix Inc.?
On this page, 4 holders' latest ownership filings report 5% or more of AdvanSix Inc.: BlackRock, Inc. (7.1%, Schedule 13G/A, filed 2026-04-24), CastleKnight Master Fund LP (6.2%, Schedule 13G, filed 2026-05-14), Dimensional Fund Advisors LP (5.2%, Schedule 13G, filed 2026-07-14) and American Century Investment Management, Inc. (5.1%, Schedule 13G, filed 2026-08-14).
Who are the largest shareholders of AdvanSix Inc.?
By the share each holder's latest filing reports, the largest holders of AdvanSix Inc. on this page are BlackRock, Inc. (7.1%), CastleKnight Master Fund LP (6.2%) and Dimensional Fund Advisors LP (5.2%).
When did BlackRock, Inc. buy into AdvanSix Inc.?
The filings give report dates, not purchase dates. The earliest filing from BlackRock, Inc. on this page is the Schedule 13G/A, filed 2026-01-08, reporting 11.9%; its latest, Schedule 13G/A filed 2026-04-24, reports 7.1%. That earliest filing is itself an amendment, which updates an earlier report.
Is this an audit or a full list?
Neither. The ownership list on this page covers only Schedule 13D and 13G filings, which holders make once they own 5% or more of a class of shares (an amendment can report a stake that has since fallen below 5%); 10 such filings are shown here. It is not an audit and not a full cap table: holders who never reached 5% are not listed, and a stake can change after its latest filing.
Also on the record for AdvanSix Inc.
| Date | Record | Figure | Our page | Source |
|---|---|---|---|---|
| April 13, 2026 | Leadership change: Patrick C. Day appointed, Chief Financial Officer | — | Leadership changes | Source |
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Where this comes from
Anyone who comes to own more than 5% of a class of a listed company's voting shares has to tell the SEC. A holder who may seek to change or influence the company files Schedule 13D, and has to say in Item 4, "Purpose of Transaction", what it intends to do. A holder with no such intent, such as many index and passive funds, may file the shorter Schedule 13G. Both are amended when the stake changes, including when it falls below 5%.
Every row here is one of those filings, linked to the filing itself. Percentages and share counts are exactly as the holder filed them, for the holder the filing names; an amendment showing a lower figure is shown as filed. Item 4 text is quoted word for word. Where a 13D's Item 4 contains a sentence stating a definite intent to influence the company, that sentence is marked and quoted; the page does not describe the holder or its motives beyond the words it filed. Nothing here is investment advice.