Claude Platform release notes - Claude Platform Docs Claude Platform Docs Messages Managed Agents Admin Resources Best practices Models & pricing CLI, SDKs, and libraries Claude API skill Release notes API reference English Console Log in Search Ctrl K Release notes Overview Migration guides Migrating to Managed Agents Console Release notes Claude Platform release notes Subscribe Copy page Updates to the Claude Platform, including the Claude API, client SDKs, and the Claude Console. Subscribe Copy page The Claude Platform release notes list changes to the Claude API, the client SDKs, and the Claude Console, newest first. For release notes on Claude Apps, see the Release notes for Claude Apps in the Claude Help Center . For updates to Claude Code, see the complete CHANGELOG.md in the claude-code repository. September 22, 2026 We've launched Claude Opus 5.5 ( claude-opus-5-5 ), a model for long-running agentic coding and knowledge work. It has a 1M token context window by default, 128k max output tokens, and always-on adaptive thinking , at $4 / $20 USD per MTok (Claude Opus 5 is $5 / $25). Claude Opus 5.5 is available on the Claude API, Claude in Amazon Bedrock , Claude Platform on AWS , Claude on Google Cloud , and Claude in Microsoft Foundry . See What's new in Claude Opus 5.5 for capabilities, API changes, and migration guidance. On Claude Opus 5.5, thinking can't be disabled: thinking: {"type": "disabled"} and thinking: {"type": "enabled", ...} return a 400 error. Omit the thinking field and control thinking depth with the effort parameter . tool_choice types any and tool also return a 400 error, as on Claude Fable 5.1; use auto with strict tool use . On the Claude API and Google Cloud, computer use on this model requires the computer_toolset_20260801 toolset and the earlier computer_20251124 tool returns a 400 error; on Amazon Bedrock, computer_20251124 keeps working. See the migration guide . Fast mode (research preview) is available for Claude Opus 5.5 on the Claude API. Tools can now be defined inside a mid-conversation system message , in beta on the Claude API with the inline-tools-2026-09-15 beta header. A tool_addition block can carry the tool's full definition ( tool: {"type": "tool_definition", "definition": {...}} ), so you can add a tool, change its schema, or move a server tool to a newer version without editing tools or invalidating the prompt cache. The same header covers adding and removing tools by reference. With the MCP connector's mcp-client-2026-09-15 beta header as well, the definition can be an MCP toolset, and a response records each server's fetched tool list in an mcp_tool_listing block, which pins that list when you send it back. September 18, 2026 The Compliance API local session endpoints now also return transcripts of Claude in Chrome sessions ( product_surface value claude_in_chrome ), in beta for Claude Enterprise organizations, with your existing Compliance Access Key and the read:compliance_user_data scope. See Sessions on users' machines . September 14, 2026 The Messages API can now compact a conversation on demand on the Claude API, in beta with the compact-2026-09-04 beta header. Send the top-level compaction parameter, and the API returns a signed compaction block that summarizes the messages you sent. On later requests, send that block first, in place of those messages. You choose when to compact, the request can run in the background, and you can keep recent turns word for word after the summary. On models with preserved thinking, the thinking in those kept turns can stay valid. With the thinking-binding-controls-2026-08-01 beta header, the input_transformations response field gains a second entry type, thinking_mismatch_allowed . It names a thinking block that failed the prefix check on a request where the API doesn't enforce that check: on Claude Fable 5.1, for example, a request from an account created before August 31, 2026, with prefix_mismatch_behavior unset. The block still reaches the model unchanged. Log these entries to find history edits in production traffic before you opt into enforcement. See Set the mismatch behavior and read input_transformations . September 10, 2026 Claude Managed Agents permission policies now include auto : the server evaluates each agent or MCP tool call and runs it, denies it, or pauses for your approval. agent.tool_use and agent.mcp_tool_use events report how each call was evaluated in an evaluation field alongside evaluated_permission . See Let the server evaluate each call with auto . Version 1.32.0 of the ant CLI adds ant beta:sessions connect , which attaches your terminal to a Claude Managed Agents session. You can follow the session live, send messages, and allow or deny tool calls that are waiting for approval. Pass --web to serve the Claude Console's session viewer locally and open the session there instead. See Connect to a Managed Agents session from your terminal . September 3, 2026 Version 1.30.0 of the ant CLI adds ant apply , which creates and updates agents, environments, skills, memory stores, and deployments from files in your repository. Describe each resource in a file, run ant apply , and approve the plan it prints. Commit the claude-lock.json lockfile it writes so that later runs, on your machine or in CI, update the same resources instead of creating new ones. See Manage resources as code with ant apply . Per-message effort changes, in beta, are also available on Google Cloud for Claude Fable 5.1, Claude Mythos 5.1, and Claude Opus 5, with the same mid-conversation-output-config-2026-07-01 beta header. September 1, 2026 We've launched Claude Fable 5.1 ( claude-fable-5-1 ), the successor to Claude Fable 5 for long-running agentic coding, knowledge work, and research, alongside Claude Mythos 5.1 ( claude-mythos-5-1 ) for Project Glasswing participants. Both models support a 1M token context window b