Key points
- Citadel filed four ownership disclosures on the same day
- The largest is in a quantum-computing company that went public in June
- A 13G shows ownership, not what the firm plans to do
A batch of new filings turned up on our hedge fund tracker on Oct. 6. Citadel put out four of them at once, all the same kind of form. Each one reports holdings as of June 30, 2026, so these are newly filed disclosures, not necessarily new purchases. What caught my eye is that one of them is a quantum-computing company.
The form is a Schedule 13G, an ownership disclosure available to certain investors reporting more than 5% of a registered share class. The largest of the four is in Quantinuum (QNT), the quantum-computing company that went public on Nasdaq in June. Citadel Advisors, the asset-management side of Ken Griffin's firm, reported 2,299,997 shares, or 7.0% of Quantinuum's Class A common stock. Those reported shares would be worth about $105 million at the Oct. 6 closing price of $45.59. Counting Citadel Securities too, the filing attributes 2,403,427 shares, or 7.3%, to Griffin.
Honeywell built Quantinuum in 2021 by merging its own quantum hardware group with a software company, Cambridge Quantum, and Honeywell still owns part of it. The company runs trapped-ion quantum computers.
The same day, Citadel reported three more, all small. It held 5.9% of rare-earth company REalloys (ALOY), shares that would be worth about $33 million at the Oct. 6 close. Citadel Advisors also reported 9.85% of Eco Wave Power (WAVE), a wave-energy company, including shares issuable through warrants. Those warrants carry an ownership limit on exercise. The smallest, 6.0% of Starfighters Space (FJET), a small space company, would be worth about $5 million at the Oct. 6 close.
Is this Ken Griffin's fund, or the market maker?
This is the part I always check first on a Citadel filing, because the name covers two very different businesses. There's Citadel Advisors, the hedge fund, and there is Citadel Securities, the market maker that handles a big share of US trading. A market maker holds stock all day as part of moving other people's orders, so its name on a filing does not automatically mean the firm is making an investment call on the company.
Quantinuum's filing separates the two businesses. Citadel Advisors reported 7.0% of the Class A shares, while Citadel Securities reported 0.3%. That shows which business reported most of the position, but doesn't tell us whether it's hedged or part of a broader trade.
A 13G is also the passive version of the form. An investor who wants to push a company to change files a 13D instead. If you want the difference in plain terms, I wrote about 13D versus 13G a while back.
What does a 13G not tell you?
Quite a bit. The filing gives the share count and the percentage as of the date it was triggered. It doesn't say why Citadel bought, what it paid, whether the shares are a plain investment or part of some other trade the firm is running, or whether it still holds the same amount today. A multi-manager firm like Citadel can hold a name for reasons that have little to do with liking the company.
So I read a filing like this as a fact about ownership on one date, not a tip. If you want the longer version of that caution, here's why copying hedge fund filings is harder than it looks. You can also follow the primary documents yourself on Quantinuum's stock page.
