That fund, his venture firm Hydrazine Capital’s fourth fund, was launched in March, and sometime before the end of June got a check from one of Silicon Valley’s more noteworthy limited partners, the University of Michigan’s $17.9 billion endowment, which has also invested directly in OpenAI and in OpenAI’s corporate venture fund, according to public filings and documents obtained by Fortune via a Freedom of Information Act request. That check is the second investment the University of Michigan has made into Altman’s venture capital firm.

The documents are notable for two reasons. First, they offer the first confirmation that Altman’s personal venture firm is investing institutional capital in addition to his own or that of his brothers and friends. Second, they go to show that the CEO of one of the hottest AI companies around has been fundraising outside his day job.

“We have a longstanding relationship with Sam and Hydrazine IV. Hydrazine IV is a small fund in which the University of Michigan is the only outside investor, and this is an extension of our ongoing investment strategies,” Dan Feder, senior managing director of investments at the University of Michigan’s endowment, told Fortune. It’s unclear the fund’s exact size or focus. Feder, OpenAI, Altman, and Hydrazine declined to share more details of the fund or didn’t respond to requests for comment. 

In a statement to Fortune, an OpenAI spokeswoman said that Altman “is fully focused on his role as CEO of OpenAI and spends only a small fraction of his time investing. He maintains transparency with the board about his occasional investments and adheres to a process for managing potential conflicts of interest.”

The University of Michigan, which over the years has collectively invested billions into funds including those managed by Sequoia Capital, Andreessen Horowitz, Accel, General Catalyst, and Y Combinator, has written two of its largest-ever venture capital fund checks into Hydrazine funds: a $105 million check into Hydrazine’s second fund and, most recently, the $75 million into Hydrazine’s fourth fund, according to a list of all the endowment’s venture capital fund investments that was provided to Fortune. The endowment has also invested $18.7 million in an investment vehicle called Apollo Projects that Altman and his brothers set up a few years ago, records show. Altman is listed as director on all of the Hydrazine funds’ disclosure documents.

Comparatively, the endowment has written a $62 million check into General Catalyst Group IX, a nearly $1.4 billion fund, according to endowment records; a $50 million check into 8VC Fund V, a $880 million fund; and a $15.3 million check into Andreessen Horowitz Fund V, a $1.5 billion fund. A review of the endowment’s venture capital investment history found that the endowment rarely writes individual checks over $50 million to individual venture capital funds, although it has done so a handful of times to firms including Y Combinator, Chengwei Evergreen Capital, and Eclipse Ventures.

Altman’s individual venture investments surfaced as an item of speculation last month amid Altman’s sudden termination, then later reinstatement, at OpenAI in November. Initially, OpenAI’s board claimed that Altman “was not consistently candid” with the board.

Altman this summer addressed his personal investing in an interview with The Information, saying he is mindful of conflicts of interest that may arise from his investments. “Generally, I think the approach to conflict of interest is just avoid things that are directly an issue with the company you’re running and disclose everything,” Altman said at the time.

Altman, a former president of Silicon Valley incubator Y Combinator before he started running OpenAI full-time, has been an investor for a long time. He set up Hydrazine Capital in 2012 with his brother and the cofounder and CEO of Lattice, Jack Altman, though it’s unclear whether Jack Altman is still an investor. Partner Ryan Cohen is also an investor at Hydrazine and Apollo Projects, according to LinkedIn. He did not respond to a request for comment.

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Clarification, Dec. 19, 2023: An earlier version of this story referred to registration materials, rather than disclosure materials.