anthropic-sdk-python v1.9.0 released — between_tools and claude-sonnet-5-5
anthropic-sdk-python v1.9.0 released on 2026-09-28 with API updates, diagnostics GA, a new model entry, streaming tool-call option, bug fixes and documentation changes.
What changed
Added between_tools thinking type; claude-sonnet-5-5 model; include_inherited and source on workspace rate limits; cache diagnostics GA; optional streaming tool calls.
Why it matters
Improves debugging and experimentation for developers working with agents, messages, and streaming tool integrations.
Who should care
DevelopersResearchers
Worth trying
Yes — Try if you need claude-sonnet-5-5 or streaming diagnostics.