Claude docs changes for May 31st, 2026 [diff]

Executive Summary

• Claude Opus 4.8 is now the default model for Max, Team Premium, Enterprise pay-as-you-go, and Anthropic API accounts, with high effort by default and /effort xhigh for the hardest tasks
• Dynamic workflows (research preview) let Claude write an orchestration script and run it across dozens to hundreds of subagents for large tasks like codebase audits or migrations
• The new security-guidance plugin reviews code changes for vulnerabilities in the same session, running checks on each edit and a deeper review on commit or push
• Auto mode is now available on the Pro plan, supporting Sonnet 4.6 alongside Opus and replacing permission prompts with background safety checks
• Fast mode now defaults to Opus 4.8 at $10/$50 per MTok, delivering ~2.5x the speed at 2x the standard rate

Claude Code changes

New Documents

whats-new/2026-w21 [Source]

Week 21 digest (May 18–22, 2026) covering releases v2.1.143–v2.1.149. Key highlights: auto mode is now on the Pro plan with Sonnet 4.6 support; /usage now shows per-category breakdown attributing usage to skills, subagents, plugins, and MCP servers; new /code-review command reports correctness bugs with optional inline GitHub PR comments; background sessions appear in /resume and stay alive when pinned with Ctrl+T; claude agents —json lists live sessions as JSON; PowerShell tool enabled by default on Windows for Bedrock/Vertex/Foundry users; /plugin marketplace shows projected context cost; new worktree.bgIsolation: "none" setting for repos where worktrees are impractical; and the allowAllClaudeAiMcps enterprise managed setting loads claude.ai cloud MCP connectors.

whats-new/2026-w22 [Source]

Week 22 digest (May 25–29, 2026) covering releases v2.1.150–v2.1.157. Key highlights: Claude Opus 4.8 is the new default model; dynamic workflows orchestrate many subagents from a script Claude writes, managed with /workflows; the security-guidance plugin provides real-time vulnerability review; fast mode now defaults to Opus 4.8; ! prefix in claude agents runs shell commands as background jobs; plugins in .claude/skills directories are auto-loaded and claude plugin init scaffolds new plugins; new /reload-skills command; skills can set disallowed-tools in frontmatter; new MessageDisplay hook event for transforming displayed assistant text; vim mode / in NORMAL mode opens reverse history search; and streaming tool execution is always enabled including on Bedrock/Vertex/Foundry.

Changed documents

claude-platform-on-aws [Source]

• Added an enterprise deployment call-to-action block near the top of the page with links to pricing plans and a contact sales form. [lines 9-11] [Source]

whats-new [Source]

• Added Week 22 entry (v2.1.150–v2.1.157, May 25–29) summarizing Claude Opus 4.8, dynamic workflows, the security-guidance plugin, and fast mode on Opus 4.8. [lines 11-19] [Source]
• Added Week 21 entry (v2.1.143–v2.1.149, May 18–22) summarizing auto mode on Pro, /usage cost breakdown, /code-review, and background session improvements. [lines 21-29] [Source]