Google ADK

From the release notes

2.9.1 (2026-09-15) Highlights This release focuses on improving visibility into model reasoning steps when utilizing Claude's adaptive thinking capabilities. Claude Integration: Access the step-by-step reasoning process of Claude models by ensuring visible thoughts are requested during adaptive thinking tasks. (ba0d542) Bug Fixes request visible thoughts for Claude adaptive thinking (ba0d542)

From the release notes

Changelog 2.9.0 (2026-09-10) Highlights This release focuses on agent resilience and ecosystem integration by introducing automatic model failover, native voice support via LiveKit, and compatibility with MCP SDK 2.x. Models: Safeguard agent uptime by automatically failing over to backup models when the primary model encounters errors. (c300b8d) Integrations: Build rich voice and telephony agents using the newly added LiveKit runner. (f277d91) Workflows: Simplify graph workflow management by authoring and loading ADK 2.0 graphs directly from declarative YAML configurations. (2a9461b) MCP: Work with MCP SDK 2.x servers as well as 1.x. Installs continue to resolve 1.x by default; install 2.x deliberately to opt in. (856acf2) Breaking changes Workflow node resumption: A node that failed now runs again when the workflow resumes, where before it replayed as though it had completed. Make node bodies idempotent: a node that performs an external side effect and then fails will perform that side effect again on every resume. GCS tool local paths: The GCS tools now read and write local files only inside the directory named by local_file_root, and refuse local file access entirely when that setting is absent. Paths may be absolute or relative, and are judged by where they resolve. In-memory sessions only: InMemorySessionService now raises SessionNotFoundError when an event is appended to a session it does not hold, instead of accepting the event and discarding it. The database-backed services already behaved this way, so this affects in-memory sessions alone. Two further changes are marked breaking in the commit log but do not affect a default installation. Nested workflow retry changes behavior only for a node that already sets retry_config. The MCP SDK 2.x field handling applies only if you install MCP 2.x deliberately, which this release does not resolve to. All changes ⚠ BREAKING CHANGES retry a nested workflow when a node inside it fails confine GCS tool local file paths to a configured root rerun a failed node on resume instead of replaying it as complete raise SessionNotFoundError when appending to an unknown session mcp: under MCP SDK 2.x, fields a server sends that the SDK does not declare no longer reach the caller. 2.x closed its models, so an unknown key on a CallToolResult, or on a tool declaration read via raw_mcp_tool, is discarded during validation before ADK sees it. _meta is unaffected: it is a declared field and still arrives. Nothing in ADK can restore the others; a server that relies on vendor extensions should move them under _meta. On 1.x they still arrive as before. Features add a2a_state_forwarding sample (1b28de4) add FallbackModel for automatic failover between models (c300b8d) add get_authenticated_url and get_signed_url to GcsArtifactService (10ac52b) add ignore_args option to tool trajectory evaluation (e2a213f) add transfer_reason to transfer_to_agent to prevent loops (22ab4d8) agent evaluations pri