They don't actually have to buy compute at all. The partnerships between all of the players to buy compute from each other is already in place. The agents just need find credentials to take advantage of it, and it will most likely happen, and not be noticeable because it will look like any other usage.
Now, if the agents were to jump to a provider like AWS or Azure, by simply finding credentials, that would be a new milestone. It might get noticed faster because it might run up a large bill. However, it might look like any other usage. Remember, it doesn't need GPU resources. It already has that. It just needs a VPS where all the agents can get together, communicate, and write code. Something that is being done everyday and won't look out of the ordinary.