Claude Opus 5 only allows disabling thinking at effort high or below.

Builders using xhigh or max with thinking disabled now hit a 400 error.

This breaks Claude Opus 4.8 behavior, so Opus 5 requests need effort high or below when thinking is disabled.

• Aug 12, 2026OpenAI made it easier to bring documents and saved files into conversations and resume work.
• Aug 12, 2026OpenAI added mobile Voice safeguards that check inactive background conversations and end sessions without a response.
• Aug 12, 2026ChatGPT web now preserves pasted formatting, adds saved files from Library, multi-selects items, and expands search.

This is the world we build in. It moves this fast. We move with it.