I tried creating a workflow in Claude 1.9255.2 (1dc8f7) 2026-05-27T01:57:20.000Z

and got

API Error: 400 messages.3.content.11: `thinking` or `redacted_thinking` blocks in the latest assistant message cannot be modified. These blocks must remain as they were in the original response.

Tried again in

Claude 1.9659.1 (193bcb) 2026-05-28T16:22:15.000Z also but may need a new chat