Claude Sonnet 5.5 Rejects Disabled Thinking

This is a small parameter change with outsized migration risk for production agent stacks.

• –`between_tools` is the lowest thinking mode and works at low, medium, and high effort.
• –It fails at xhigh or max effort, where adaptive thinking must be used instead.
• –Tool-driven applications may now receive progress updates inside `thinking` blocks.
• –Existing integrations should update configuration before switching model IDs to avoid runtime failures.