Tesla isn't that profitable, but SpaceX is likely generating boatloads of cash. From what I can tell Starlink alone has a free positive cash flow of about $2 billion. I'm not sure what the launch business is worth, but it's likely a lot given the absence of domestic competition.

I have a suspicion the reason Musk wanted to combine SpaceX and X.ai is the latter gives him losses to write off against all that cash from the former plus a chance for a big AI payoff.