Opus 5.5 Progress Updates: Stop Silent Agent Turns

Claude Opus 5.5 shipped on September 22 and most of the chatter has been about price: $4/$20 per million tokens, cheaper than Opus 5, and on par with Fable 5.1 on most agentic work. The complaint showing up in GitHub issues and dev threads since then is quieter, literally. Agent UIs that used to stream a line like "Tests fail in auth.py, reading it now" between tool calls have gone silent. No error, no 400. The spinner just sits there for thirty seconds while the agent works.

The cause is a response-shape change. On Opus 5 the short notes Claude writes between tool calls came back as text blocks. On Opus 5.5 (and Fable 5.1) they come back as progress-update thinking blocks, and at the default thinking.display of "omitted" their text is empty. Your code still works. Your users just can't see anything.