39 releases from to
Everything Anthropic shipped in September 2026, collected from official Anthropic sources. Each entry is dated and links to the page it came from.
Anthropic launched Claude Fable 5.1 and Mythos 5.1, advanced models for coding and knowledge work. They also released Claude Opus 5.5 and Claude Sonnet 5.5, with enhanced capabilities. Cache Diagnostics moved to general availability, and Admin API methods exited beta.
Summary generated from the releases listed below.
September 2026 was Anthropic's busiest month of the 12 months to then: 39 releases, about 3.6× its monthly average of 11. That was 26 releases more than August 2026. Most were Developer Tools (17), followed by API (9) and Infrastructure (5).
Releases
39
+26 vs August 2026
Rank of 12 months
1st
Average 10.8 a month
Most shipped
Developer Tools
17 releases
Launched Claude Sonnet 5.5, a faster, lower-cost complement to Claude Opus 5.5 in the Claude 5.5 family.
Source: Claude Help Center Release NotesLaunch of Claude Opus 5.5 (claude-opus-5-5) for long-running agentic coding and knowledge work. Features 1M token context window, 128k max output tokens, and adaptive thinking. Available on multiple platforms.
Source: Claude Platform Release NotesLaunched Claude Fable 5.1 and Claude Mythos 5.1, world's most advanced models for coding and knowledge work.
Source: Claude Help Center Release NotesNewest first. Each entry links to the official page it came from.
Admin API methods for organization info, members, invites, workspaces, API keys, rate limits, service accounts, workload identity federation, customer-managed encryption keys, and compliance settings are out of beta. Deprecation of Claude Sonnet 4.5 with retirement on November 3…
Admin API methods for organization management exit beta in SDKs. Deprecated Claude Sonnet 4.5 with retirement scheduled for November 30, 2026.
Deprecation of Claude Sonnet 4.5 model (claude-sonnet-4-5-20250929) with retirement on Claude API scheduled for November 30, 2026. Recommended migration to Claude Sonnet 5.5.
In Python SDK 1.10.0, TypeScript SDK 0.130.0, C# SDK 12.52.0, Go SDK 1.77.0, Java SDK 2.67.0, PHP SDK 0.53.0, Ruby SDK 1.75.0, and version 1.37.0 of the ant CLI, the Admin API methods for organization info, members, invites, workspaces, API keys, rate limits, service accounts, w…
Admin API methods for organization management move out of beta. Available under client.organization and ant organization.
Admin API methods for organization management moved out of beta for multiple SDKs and CLI tools.
Launched Claude Sonnet 5.5, a faster, lower-cost complement to Claude Opus 5.5 in the Claude 5.5 family.
You can now submit plugins to the Claude directory through a new developer portal, track them through review, and see usage analytics once they’re live.
The Compliance API local session endpoints are out of beta for Claude for Microsoft 365 sessions in Excel, PowerPoint, Word, and Outlook ( product_surface values beginning with office_agents ).
Compliance API activity feed changes to remove file names and document titles from activity objects
Cache diagnostics feature moved out of beta on Claude API with new diagnostics object implementation. Compliance API local session endpoints expanded to include Chrome sessions.
Anthropic resumed billing for refusals that arrive before any output in the bio, frontier_llm and reasoning_extraction categories, on all platforms. The Compliance API local session endpoints for Claude for Microsoft 365 sessions are out of beta.
Resumed billing for refusals that arrive before any output when stop_details.category is "bio", "frontier_llm", or "reasoning_extraction". Refusals billed under this change are charged like any other request.
Cache diagnostics beta removal and new diagnostics field implementation on Claude API.
Cache diagnostics feature moved out of beta with new diagnostics object requirements
Cache diagnostics exited beta on Claude API and no longer requires beta header.
Launch of Claude Opus 5.5 (claude-opus-5-5) for long-running agentic coding and knowledge work. Features 1M token context window, 128k max output tokens, and adaptive thinking. Available on multiple platforms.
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 eval…
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.
Compliance API local session endpoint updates and activity feed changes for Claude for Microsoft 365.
Cache diagnostics response format updated to always include diagnostics field. Compliance API Activity Feed now omits file names and titles for privacy compliance.
Enhanced cache diagnostics response structure for requests with beta header. Added consistent diagnostics field.
For cache diagnostics, a response to a request that sends the cache-diagnosis-2026-04-07 beta header now always includes the diagnostics field. The field is null when the request did not include the diagnostics object. Previously the field was omitted in that case.
Cache diagnostics changes: diagnostics field always included in responses. Fingerprint stored only when diagnostics object is included.
Cache diagnostics beta update with inline-tools-2026-09-15 header for defining tools in mid-conversation system messages.
You can now ask for a design, deck, or document in any conversation with Claude, including in Claude Code and the Artifacts tab, and edit it with Claude or directly as you work. Claude Design works inside your conversations with all of its features, including on-canvas editing a…
Rolled out Claude Cowork experience making all features available in any conversation with cross-platform support for Pro/Max plans.
Launched Salesforce plugin with 37 pre-built sales skills for managing accounts, opportunities, and pipeline through Claude.
Messages API compaction beta with compact-2026-09-04 header and thinking-binding-controls-2026-08-01 beta features.
Messages API introduced conversation compaction feature via beta header. Added support for mid-conversation tool definitions and MCP toolset integration.
Introduced smart reports analyzing team Claude usage patterns, costs, and friction points for Enterprise plans.
Updated permission policies for Claude Managed Agents with new networking restrictions and tool usage controls.
Claude Managed Agents permission policies now include auto evaluation for agent/tool calls
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 ses…
Cache diagnostics fingerprint changes and request fingerprint storage updates for Claude API.
ant CLI version 1.30.0 with apply command for resource management and deployment.
ant CLI v1.30.0 adds ant apply for managing resources as code
New ant CLI commands for managing resources as code with repository integration
Launched Claude Fable 5.1 and Claude Mythos 5.1, world's most advanced models for coding and knowledge work.
Anthropic releases per month, for September 2026 and the 11 months before it. A taller bar means more releases that month; the dated entries for each month are on its own page.
26 of the companies we track shipped in September 2026; Anthropic ranks 1st by number of releases.
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