IANAL but it seems plausible they could argue that the 50% was for the original concept and all the work he had done on it up to that point. Or are they really arguing that they threw all that away and started with nothing after he left? I agree with those saying that ideas don't make a company, but startup companies don't suddenly become worth a billion real dollars to GM without ideas. If what GM is buying is largely IP, and that IP is largely based on the departed co-founder's ideas, then his claims seem reasonable to me.

Edit: reading further I guess they are arguing that none of his IP is in what GM is buying. So I guess that will be the real point of contention.

I don't think this is true. Unless said contract specifically says that your 50% of the share is contingent upon a list of explicitly spelled out contributions, you would actually be entitled to the 50% even if you did nothing.

I don't think one month of work should be worth 50% of the company, but it looks like he did actually do work. And he never got compensated for it.

The issue is (assuming what Jeremy says is true) that he was forced out after 1 month with no say in the matter, no agreement & no buyout of stock.

So while 1 month probably shouldn't be worth 50% of the company, you also can't just decide that you don't want your co-founder to have a stake in your company any more, and push them out.

At the end of that 1 month, they had both done equal work (about a month's worth) and had equal share (50% each). It sounds like (according to Jeremy's story) he still owns that because no one agreed to a formal change in ownership.

Yes, but what if, for example, the work that he had done prior to beginning that one month's involvement in Cruise was the majority of the IP that GM wants to buy? Would you still interpret it the same way? I have no idea whose IP is in there, at all. Just pointing out that simply stating he did "a month's work" could be quite disingenuous.

Claim 27 of this response enumerates the (claimed) consideration.

Yes, I know. I was only pointing out that the issue is more complicated than having an agreement that lays out a 50/50 split.