This is one of the things I dislike about managed agents.
Is it the best DX? yes.
Is it now much, much more usable because it's bring your own sandbox? yes (most startups now have Sandbox credits and want to use them).
But if something like this happens, I'm responsible to my users, not Anthropic.
I think limiting yourself to one LLM provider is a bad idea at this point.
YC startups also can't use it because they have 2M to spend on OAI and the lock-in is too strong.
If you're building agents, look at LangChain DeepAgents. It's the best platform that looks better than anything I have seen so far, but managed DeepAgents are still behind a waitlist so I have. been unable to test.