As part of their investment, Microsoft gained access to the full OpenAI codebase

While I don’t think Musk is saying OpenAI agreed to give them the source code but that because they’re hosted on Azure they have access to everything.

He clarified in a reply to the tweet: “ChatGPT is entirely housed within Microsoft Azure. When push comes to shove, they have everything, including the model weights.”

Microsoft is a pirate boat of lawyers.