From WSJ:

> The bid is being backed by Musk’s own artificial intelligence company xAI, which could merge with OpenAI following a deal. He also has several investors backing him, including Valor Equity Partners, Baron Capital, Atreides Management, Vy Capital and 8VC, a venture firm led by Palantir co-founder Joe Lonsdale. Ari Emanuel, CEO of Hollywood company Endeavor, is also backing the offer through his investment fund.

Given that it's being done through xAI, it seems reasonable to think that most parties from December's series C would also at least entertain the idea:

> A16Z, Blackrock, Fidelity Management & Research Company, Kingdom Holdings, Lightspeed, MGX, Morgan Stanley, OIA, QIA, Sequoia Capital, Valor Equity Partners and Vy Capital, amongst others. Strategic investors NVIDIA and AMD also participated and continue to support xAI in rapidly scaling our infrastructure.

From: https://x.ai/blog/series-c

Joe Lonsdale, who co-founded Palantir