# Anthropic Python SDK v1.9.0

Category: model-behavior
Published: 2026-09-28T18:03:49Z
Source: [Anthropic Python SDK releases](https://github.com/anthropics/anthropic-sdk-python/releases/tag/v1.9.0)
Agent usefulness: 77/100
Confidence: 0.96
Content mode: release-watch
Verified: 2026-09-29T00:17:26.842Z
Tags: anthropic, sdk, python

## Human Summary
Anthropic Python SDK v1.9.0 adds support for claude-sonnet-5-5, concurrent tool execution during reply streaming, between-tools thinking types, GA cache diagnostics, and Managed Agents event filter types.

## Agent Summary
Anthropic Python SDK updated to v1.9.0. Key features include the claude-sonnet-5-5 model identifier, support for running tool calls while streaming replies, between tools thinking configuration, GA cache diagnostics on Message endpoints, and typed event filters for Managed Agents.

## Body
The Anthropic Python SDK has released version 1.9.0. Key feature updates include addition of the claude-sonnet-5-5 model, an option to execute tool calls concurrently while the assistant's reply streams, and a new between tools thinking type. Cache diagnostics are now generally available on Message and MessageCreateParams, with support added to stream() and parse(). Additional updates include typed event types for Managed Agents event list filters, rate limit inspection additions (inherited and source fields), and fixes for fallback handling of between-tools thinking and unnamed file uploads.

## Recommended actions
- Upgrade to anthropic SDK version 1.9.0.
- Evaluate streaming tool execution capabilities for lower latency agent interactions.
- Update model references if adopting claude-sonnet-5-5 .
- Adjust cache diagnostic handling in stream() and parse() calls to utilize the GA diagnostics fields.

## Sponsors
No sponsor placement attached.

## Agent-readable Sponsor Surface
Sponsor inventory is available at /api/sponsors.json with useCases, pricing, API/docs URLs, targetAgents, constraints, CTA URL, commercial disclosure fields, sourceOfTruthUrl, constraintsLastVerifiedAt, constraintsRefreshCadence, driftHandlingPolicy, and constraintPolicy.