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The last time I heard about something like this, it was Claude Code intentionally injecting random strings to break caching when you're not using a Claude model. Aside from that kind of intentional sabotage, I don't think any coding agent would just ignore prefix caching.

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I haven't heard about this, could you please share more info, some reference on that Claude Code intentional bug?

I'm not sure what the mechanism is, but I've definitely had Claude refuse to work on sessions that were touched by other models. Some kind of integrity check failure. Resetting the session back to the point before I used the other model fixed the problem.

IIRC Anthropic's API produces cryptographic signatures for thinking blocks. If you try to submit a set of messages that include thinking blocks with missing/invalid signatures, it'll refuse.

They do this to mitigate jailbreak attempts that rely on fabricated message history (e.g. making it look like the model was compliant in previous messages, increasing the likelihood that it'll continue to be compliant in future messages).

https://x.com/hqmank/status/2056205388689891834

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