Claude Code — September 2026 Releases
27 releases in September 2026.
What's new in Claude Code, September 2026
Claude Code adds new default models, a /diff panel and AGENTS.md support
Claude Code's September 2026 releases changed the default models, added a side-by-side /diff panel and made AGENTS.md readable as project instructions. Twenty-seven releases shipped, from v2.1.257 to v2.1.286.
Model defaults moved three times: Claude Fable 5.1 (v2.1.257), Claude Opus 5.5 (v2.1.280) and Claude Sonnet 5.5 (v2.1.284), each with 1M context. Day to day, fullscreen mode gained a /diff panel for uncommitted changes, /cost and the status line now show a likely cause for prompt-cache misses, and ctrl+enter sends all queued messages at once. In projects with no CLAUDE.md, AGENTS.md is read instead. Plugin work included claude plugin eval and claude plugin configure.
Administrators got managed settings such as managedMcpServers, deniedModels, availableModelsMatch and allowedProviders, plus many Claude apps gateway options. Several releases fixed regressions affecting proxy and gateway setups, macOS 12 launch and session resume.
- Defaults changed: Claude Fable 5.1 (v2.1.257), Claude Opus 5.5 (v2.1.280) and Claude Sonnet 5.5 (v2.1.284), each with 1M context
- /diff opens a panel beside the conversation in fullscreen mode showing uncommitted changes (v2.1.260)
- AGENTS.md is read as project instructions when a project has no CLAUDE.md (v2.1.277)
- Send-now key (ctrl+enter or ctrl+x ctrl+s) interrupts the turn and sends all queued messages (v2.1.275)
- claude plugin eval runs a plugin's eval suite and produces scored JSON and HTML reports (v2.1.269)
- Managed settings deniedModels, availableModelsMatch and allowedProviders restrict which models and providers can be used (v2.1.283, v2.1.285)
Upgrading from v2.1.252? See every change through v2.1.286.
- v2.1.286 (September 30, 2026) — Claude Code 2.1.286 makes permission requests clearer when multiple stack up, and fixes critical issues where login credentials weren't properly refre
- v2.1.285 (September 29, 2026) — Claude Code 2.1.285 makes it easier to launch the desktop app directly from your terminal and gives you more control over plugin configuration right a
- v2.1.284 (September 28, 2026) — Claude Code 2.1.284 now uses the faster Claude Sonnet 5.5 model by default, giving you improved performance with a massive 1M context window. We've al
- v2.1.283 (September 25, 2026) — Claude Code 2.1.283 makes it easier to manage which AI models your team can use, with new controls to lock in specific versions and block others—keepi
- v2.1.282 (September 24, 2026) — Claude Code 2.1.282 makes reading easier with smarter text formatting in wide terminals, while giving you better visibility into what telemetry settin
- v2.1.281 (September 23, 2026) — Claude Code 2.1.281 brings improved desktop security controls and cross-account AWS access, making it easier to manage permissions and work across dif
- v2.1.280 (September 22, 2026) — Claude Code 2.1.280 brings Claude Opus 5.5 as your new default model with a massive 1M context window and faster processing, plus improved mouse contr
- v2.1.278 (September 19, 2026) — Claude Code 2.1.278 now runs auto mode more efficiently by defaulting to server-side processing, which means no extra charges for most users. We've al
- v2.1.277 (September 18, 2026) — Claude Code 2.1.277 now reads AGENTS.md as project instructions when CLAUDE.md isn't present, making it easier to configure your setup. We've also imp
- v2.1.276 (September 18, 2026) — Claude Code 2.1.276 fixes a critical issue that was causing all requests to fail when using proxy or gateway setups. We've resolved the input tag erro
- v2.1.275 (September 17, 2026) — Claude Code 2.1.275 streamlines authentication with account confirmation before saving credentials and adds a quick send-now key to interrupt and disp
- v2.1.274 (September 16, 2026) — Claude Code 2.1.274 now alerts you when memory is running critically low with clear steps to free up space or safely restart. We've also fixed a frust
- v2.1.273 (September 15, 2026) — Claude Code 2.1.273 now automatically reconnects when MCP servers disconnect and notifies you if it can't recover, plus you can fork remote-control se
- v2.1.272 (September 14, 2026) — - Bug fixes and reliability improvements
- v2.1.271 (September 14, 2026) — Claude Code 2.1.271 brings faster remote coding sessions with a new fast mode that lets you speed up your work in cloud and self-hosted environments.
- v2.1.270 (September 12, 2026) — Claude Code 2.1.270 fixes an annoying bug where git commands would unexpectedly ask for permission during long sessions. We've also made several under
- v2.1.269 (September 11, 2026) — Claude Code 2.1.269 now lets you evaluate plugins with reproducible, scored results and gives you more control over how output appears across differen
- v2.1.268 (September 10, 2026) — Claude Code 2.1.268 brings unified pricing across your Claude apps gateway with automatic rate matching, plus new security safeguards that warn you ab
- v2.1.267 (September 9, 2026) — Claude Code 2.1.267 gives you new control over resource usage with effort level limits across all providers, plus better ways to fine-tune your prompt
- v2.1.266 (September 8, 2026) — Claude Code 2.1.266 resolves a critical authentication issue that broke proxy and gateway setups in the previous version. We've restored the proper be
- v2.1.265 (September 8, 2026) — Claude Code 2.1.265 now lets you point to entire plugin folders that automatically load child plugins and pick up changes in real-time, plus adds smar
- v2.1.263 (September 6, 2026) — - Bug fixes and reliability improvements
- v2.1.261 (September 4, 2026) — - Added an "Organi
- v2.1.260 (September 3, 2026) — Claude Code 2.1.260 now shows your uncommitted changes in a side-by-side diff panel, making it easier to review edits as they happen. We've also impro
- v2.1.259 (September 2, 2026) — - Added managedMcpServers managed setting: organi
- v2.1.258 (September 1, 2026) — Claude Code 2.1.258 fixes critical issues that were preventing the app from launching on older Mac systems and resolving remote session failures. Thes
- v2.1.257 (September 1, 2026) — Claude Code 2.1.257 now includes Claude Fable 5.1 as the default model with expanded context and improved pricing, plus new customizable time format s