Citadel bought Leopold Aschenbrenner's stock book. Two outlets say he kept part of it, and a filing due Monday settles it.

Update, July 30, 1 p.m. ET: This piece published Thursday morning under a headline saying nobody had named the buyer. Bloomberg and Reuters named it a few hours later, and the article below has been rewritten around the answer. The filing calendar still runs, and the first date in it now carries more weight than it did at 10 a.m.

The name arrived well ahead of the paperwork, which is the reverse of how this usually goes. Bloomberg reported Thursday that Ken Griffin's Citadel bought the bulk of the AI stocks held by Leopold Aschenbrenner's Situational Awareness. Reuters had the same story and the same word. A representative for Citadel declined to comment, and the price has stayed private.

So there's a name. What it bought is still a range, and the range is the part I find genuinely interesting, because the SEC calendar is about to narrow it for us.

Three accounts, one word apart

At mid-morning, CNBC's David Faber described the trade as the entire public equities book, the long positions and the short ones together, moved in one block to a single buyer. Bloomberg's version is tighter on both ends. It says Citadel took the bulk of the stock positions, and it says Situational Awareness still holds public stock. Reuters put bulk in its headline as well.

Everyone agrees on the shape: a leveraged fund emptied out under pressure from its lenders, with prime brokers at Bank of America, Goldman Sachs and JPMorgan Chase marketing the holdings before Thursday's open. They disagree on the remainder. Bulk leaves something behind, and whatever got left behind is the part carrying hard reporting deadlines. Four dates matter, and the first is Monday.

Monday, Aug. 3: a Form 4 on a microcap

Start with the smallest position, because it has the fastest clock. On June 29 the fund disclosed 19.9% of SharonAI Holdings (SHAZ), a two-year-old GPU cloud company in New York with 30 employees and a market value under $2 billion. A Form 4 filed July 2 shows it exercised 3.7 million pre-funded warrants on June 30 at a hundredth of a cent each, leaving 5,396,127 shares.

One field on that Form 4 matters more than the rest, and it's a checkbox. The fund ticked "10% owner," which puts it inside Section 16 of the Exchange Act, and against SharonAI's current 35,183,961 shares outstanding those 5,396,127 shares work out to about 15%, so it stays inside. Section 16 gives a 10% owner two business days from the trade date to report a sale on a Form 4. The deadline is hard, and a filing on the third business day is simply late. A Thursday trade means Monday, Aug. 3. EDGAR accepts filings until 10 p.m. Eastern, so the window closes Monday night.

A Form 4 names the seller and gives a price. It leaves the buyer out. Even so, it's the document that settles which of Thursday's two accounts is closer to right. SharonAI trades about 2.4 million shares a day, so a 15% stake in a company that size behaves more like a private holding than a liquid line a block desk clears in an afternoon. A filing Monday night means the stake went with everything else, and Faber's "entire book" holds up. A quiet Monday points the other way, toward bulk, and toward a remainder that'll have to be described eventually.

Thursday, Aug. 6: Citadel's own deadline

This is the date that puts Citadel's name on a document instead of in a news story. Anyone who crosses 5% of a company's stock owes the SEC a Schedule 13D or 13G, and since February 2024 both are due within five business days. Counting from Thursday, that lands on Aug. 6.

Whether it fires depends on the sizes Citadel took. A firm that absorbed a book this size and spread it thin can sit under 5% everywhere, in which case Aug. 6 passes quietly. A firm that took Aschenbrenner's largest stakes intact crosses the line and files, giving its address, its structure and the exact size of the position. The rules reward speed elsewhere too. A 13D amendment is now due within two business days, tightened from a standard that used to say "promptly," which in practice meant whenever counsel got to it.

Worth separating two companies with the same name here, because people mix them up constantly. The Citadel in this story is Griffin's hedge fund, which files quarterly holdings reports under Citadel Advisors LLC. Citadel Securities, the firm that handles a large share of US retail stock orders, is a separate business. Reports on Thursday pointed at the hedge fund.

Friday, Aug. 14: a portrait of a dead portfolio

Quarterly holdings reports run 45 days behind the quarter, so Situational Awareness's June 30 filing is due Aug. 14. It'll be a complete account of what the firm owned five weeks before it sold.

That one is worth waiting for because of what the March 31 version already showed. It listed 42 positions worth $13.68 billion, with $8.46 billion of that in put options against Nvidia (NVDA), Oracle (ORCL), Broadcom (AVGO), AMD and a chip fund. The June 30 version covers the quarter in which the fund reached its peak, and it's the last full inventory anyone outside the firm will see of the book as it was actually built. The obligation also outlasts the portfolio. Once a manager crosses $100 million in reportable securities, the rule keeps it filing through the first three quarters of the following year, so Situational Awareness is on the hook into 2027, with quarterly filings from a firm whose public book sits mostly empty.

Monday, Nov. 16: where Citadel's side lands, and disappears

Citadel has to report these holdings too, on the same 45-day schedule. Its Sept. 30 filing is technically due Nov. 14, which falls on a Saturday, so the real deadline is Monday, Nov. 16. That document will contain the stakes it bought Thursday, assuming it still holds them in six weeks.

Finding them in there is another matter. Our own hedge fund tracker parsed Citadel's most recent quarterly report, filed May 15 for March 31 positions, into 12,857 separate positions worth $618.5 billion. Aschenbrenner's entire disclosed book, at $13.68 billion in March, would be about 2% of that. A few billion dollars of chip and power stocks arriving inside a filing that size is a rounding difference, and nothing in the form flags where a position came from. That's why the Aug. 6 date is the one to watch. A 5% threshold filing names a company and a date. A November 13F just lists what Citadel owns, alongside everything else it owns.

The complication hiding in the share count

The fund's largest disclosed stake was 12,410,060 Class A shares of Nebius Group (NBIS), reported May 27 as 5.6% of the company. That percentage rested on 220,406,311 shares outstanding as of March 31. Nebius has issued stock since. The count now sits near 251.7 million, and the same 12,410,060 shares come to roughly 4.9%. If that math held on the day of the sale, the fund had already drifted under the 5% line through dilution alone, and its exit falls outside the fast deadlines entirely. The amendment would instead be due 45 days after the quarter ends, which points to mid-November.

So the same 12.4 million shares are a reportable position or an invisible one, depending on arithmetic the issuer controls. That's filing-watching in one example.

What the calendar will still leave out

One category of position stays dark through all of it. Bets made by borrowing a stock and selling it sit outside every form listed here, and CNBC reported that positions against software companies including Adobe (ADBE) were part of what went wrong. That side of the book will stay a matter of reporting alone. The price is likely to stay private as well. A Form 4 would give a price for one microcap, while the terms of a multibillion-dollar block between two private firms stay between them. Situational Awareness also keeps its private holdings, the largest of which is a stake in Anthropic that the Financial Times valued at about $5 billion, and private stakes appear on none of these forms.

Four dated documents in three months is unusually fast for this corner of the market, where the normal answer to "who owns this" is a 13F that arrives six weeks after it stopped being true. We'll be reading each one as it lands. The first one's Monday night.

Our Citadel page tracks its filings as they hit EDGAR, and our Situational Awareness page does the same on the other side of the trade. The Nebius stock and filings page covers that stake specifically. We wrote up the sale itself and what the fund's last filing showed on Thursday morning. If you're new to reading these forms, our explainer on what a 13F does and doesn't tell you is the place to start, and our look at whether copying hedge fund disclosures actually works is worth reading before acting on any of it.

Sources

• Bloomberg, July 30, 2026: Citadel bought the bulk of Situational Awareness's AI stock positions; the fund has not sold all of its public stock and retains private stakes including Anthropic; a Citadel representative declined to comment. Reuters reported the same day that Citadel bought the bulk of the stock portfolio.
• CNBC, David Faber, July 30, 2026: the entire public equities book, longs and shorts, sold in one block trade to a single buyer; prime brokers at Bank of America, Goldman Sachs and JPMorgan Chase marketing the holdings before the open; bets against software including Adobe.
• SEC filings by Situational Awareness LP: Form 4 filed July 2, 2026 (10% owner box checked, 5,396,127 SharonAI shares held), Schedule 13G on SharonAI filed June 29, 2026, Schedule 13G on Nebius filed May 27, 2026, and Form 13F-HR filed May 18, 2026.
• SEC beneficial ownership amendments effective Feb. 5, 2024: initial Schedule 13D and 13G within five business days, 13D amendments within two business days, EDGAR cut-off extended to 10 p.m. ET. Section 16(a) and Rule 16a-3: Form 4 due within two business days of the trade date. Rule 13f-1: quarterly reports due 45 days after quarter end.
• Citadel Advisors LLC Form 13F-HR filed May 15, 2026, as parsed by our own fund tracker: 12,857 positions, $618.5 billion.