Shipped. Daily — June 5, 2026

SDK middleware lands across all TypeScript platforms; Opus 4.1 formally deprecated; Claude Code ships twice.

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Claude Code v2.1.166: fallback models and a quiet security tightening

The feature is fallbackModel. Configure up to three alternative models tried in order when your primary model is overloaded. Production agent teams have been assembling this logic manually for months. Now it is a config setting.

The same build hardens cross-session messaging. Relayed messages no longer carry user authority. Quiet, non-headline, load-bearing. Glob patterns now work in deny rule tool positions, so a single "*" blocks every tool in one line. Retry on unexpected non-retryable API errors is in. Fixes ship for JetBrains IDE flickering (2026.1+), remote session registration hangs, and Kitty keyboard protocol Shift drops. Source: github.com/anthropics/claude-code/releases

v2.1.165 shipped earlier the same day, at 05:45 UTC. Bug fixes only. Nothing user-facing.

Release Log

All Anthropic releases in the past 24 hours.

Claude Code

2026-06-06 00:55 UTC CODE

Claude Code v2.1.166

Fallback model configuration (fallbackModel): up to three alternatives tried in order on primary-model overload. Glob pattern support in deny rule tool positions ("*" denies all tools). Cross-session messaging security hardened: relayed messages no longer carry user authority. MAX_THINKING_TOKENS=0 and --thinking disabled suppress thinking on models that think by default. Retry mechanism on unexpected API errors. claude update now announces target version before downloading. Fixes for image processing errors, remote session registration hangs, JetBrains IDE flickering (2026.1+), and Kitty keyboard Shift+non-ASCII drops.

How to use: claude update

2026-06-05 05:45 UTC CODE

Claude Code v2.1.165

Bug fixes and reliability improvements. No user-facing feature changes.

TypeScript SDKs

2026-06-05 19:48 UTC SDK-TS

@anthropic-ai/sdk v0.101.0

Client middleware support added to the HTTP stack. Streaming fix: stop_details now carries through beta message_delta accumulation correctly. JSON number parsing fixed for scientific notation. Security reports now route to Anthropic's HackerOne program.

How to use: npm install @anthropic-ai/sdk@0.101.0

2026-06-05 19:48-19:49 UTC SDK-TS

vertex-sdk v0.17.0 / foundry-sdk v0.3.0 / bedrock-sdk v0.30.0 / aws-sdk v0.4.0

All four platform-specific TypeScript wrappers ship the same pair of changes: Claude Opus 4.1 marked deprecated, client middleware support added.

How to use: Update to the latest version for your platform. Audit any explicit Opus 4.1 model string references before the retirement window closes.

Python SDK

2026-06-05 SDK-PY

anthropic v0.106.0

Claude Opus 4.1 formally marked deprecated. Foundry client copy() and with_options() methods fixed. Schema transform fix: $defs preserved when schema root is a $ref. Security reports now route to HackerOne.

How to use: pip install anthropic==0.106.0

Quiet on the Wire

No new posts from anthropic.com/news or anthropic.com/research in the window. Most recent news item: June 3, Claude Partner Network Services Track and Partner Hub launch. The S-1 IPO filing from June 1 has produced no follow-on public announcements.

Docs endpoints (docs.anthropic.com) returned HTTP 403 on direct fetch during this sweep. API release notes, Claude Apps release notes, and system prompt updates may contain changes not captured here. Last confirmed access: not available for this window.

Claude Code v2.1.166: fallback models and a quiet security tightening

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