Claude sonnet 4.6 prefill error

[ghar1821]

I tried using the A1 agent with sonnet 4.6 model, but only got 400 error. The message is something along the line of "this model does not support assistant message prefill".

Most likely related to this: https://www.reddit.com/r/LLMDevs/comments/1r0ih5p/opus_removes_lastassistantturn_prefill_you_can_no/