Cursor has no AI services, they do not develop their own frontier models. I see no reason to understand why $10bn for Cursor's services is an advantage xAI versus say a $10bn deal with Anthropic, OpenAI or Google.
Those other companies wouldn't also toss in a purchase option.
But I agree that it's hard to articulate what Cursor services you could blow this much money on.
Maybe it is all just an option! Or maybe they get a bunch of IP either way?
It's true that Cursor doesn't have their own frontier models, but they are training their own models. They just aren't at frontier level yet. The $60B/$10B deal looks like a bet that this is a capital/GPU constraint rather than a capability one.