Verification Report

September 12, 2026 release refresh

Updated for Claude Code v2.1.263–v2.1.269 (September 6–11). npm checked on September 12, 2026 KST: latest/next=2.1.269, stable=2.1.236. Keep latest-feature evaluation separate from a team's stable-channel rollout.

• Plugins: claude plugin eval produces JSON and HTML evaluation reports; install, uninstall, update, enable, and disable accept --json. --plugin-dir can point to a parent directory containing multiple plugins.
• Commands and settings: /output-style [name] works over Remote Control and in cloud/headless sessions. maxEffortLevel caps effort globally or per model under modelSettings. bashEditDiffEnabled adds file-edit diffs to Bash results.
• Recovery and compatibility: 2.1.266 fixes forced gateway sign-in; 2.1.268 fixes HTTP 400s on Anthropic-compatible endpoints introduced in 2.1.265. /goal retries with backoff or pauses with a reason after API, network, or usage-limit failures.
• Permissions and operations: fixes cover symlink deny/ask rules, Bash tee write boundaries, and secrets in MCP/plugin errors. WebFetch has a default 300-second deadline. /ultrareview --post posts the PR comment directly when findings arrive.

Sources: official changelog, npm dist-tags.

This refresh compares official release text with npm channels. It does not claim local CLI execution or live feature testing. Tables below retain prior dated checks; the channel values above supersede them.

The English locale should behave as a first-class locale for supported content and as unavailable for unsupported books.

Expected Behavior

• /en renders the English home page.
• /en lists only English-localized handbooks.
• /en/books/claude-code-advanced renders English content.
• /en/books/claude-code-command-master renders English content.
• /en/books/codex-advanced does not fall back to Korean content.
• The preview chapter API receives a locale parameter.
• Sitemap generation includes English URLs only for English pages.

Local Checks

Run the focused handbook checks after changing locale routing or content availability:

yarn workspace handbook typecheck
yarn workspace handbook lint
yarn workspace handbook build
yarn workspace handbook test:e2e

If an E2E test fails, inspect whether it is asserting Korean-only copy or a route that is now locale-specific.

Content Checks

• Every English page has English frontmatter.
• Internal links use /en/books/....
• Korean-only books are not registered in content/books/en/meta.json; translated books are.
• The home catalog uses localized availability from the MDX source.
• Language links appear only when the same page exists in more than one locale.
• Claude Code content uses the 2026-09-05 check baseline: v2.1.261 (latest and next) and v2.1.236 (stable) from npm dist-tags, plus the official changelog through v2.1.261 and the Claude Fable 5.1 overview, what's-new, migration guide, and announcement.
• The v2.1.252~261 refresh covers Fable 5.1 as the default Fable model (released 2026-09-01, minimum v2.1.255, default from v2.1.257), gateway sessions staying on Fable 5, the category-based classifier fallback table (biology to Opus 5, cybersecurity to Opus 4.8, switchModelsOnFlag), Fable 5.1 Messages API breaking changes and additive features, $0.25/MTok cache reads, the /effort session-only s key, no default-effort hold on Opus 5 and Fable 5.1, CLAUDE_CODE_SUBAGENT_MODEL_FORCE, the v2.1.260 picker/prompt-cache/[1m] fixes, 1M auto-compact timing, and the Mythos 5.1 access distinction. Fast mode stays Opus 5/4.8 only.
• The v2.1.239~247 refresh covers loop usage statistics, managed model/cache controls, Auto-mode rules, partial subagent continuation, headless recovery, feedback drafts, and security hardening.
• The v2.1.221~237 refresh covers interactive fork/background spawn defaults, cross-session messaging and session mentions, self-hosted runners, GitLab MR workflows, ANTHROPIC_DEFAULT_MODEL, the Concise output style, newer-model Task/Todo defaults, and trust/sandbox/OAuth/Remote hardening.
• The v2.1.206~v2.1.220 refresh covers Opus 5, the /fork and /subtask split, session/concurrency/depth limits for subagents, strict network allowlisting, optional filesystem isolation, DirectoryAdded, headless MCP validation errors, and nested subagent stream forwarding.
• The v2.1.181~v2.1.205 refresh covers Sonnet 5, org default model labeling, sandbox credentials, destructive-command sandbox auto-approval, Windows PowerShell sandbox fixes, MCP login/logout, MCP idle timeout, model restrictions, deprecated-model warnings, nested-agent/background stability, Korean paste handling, and non-interactive fallback fixes. v2.1.198–201 add background-by-default subagents, Claude in Chrome GA, the /dataviz skill, the default permission mode "Manual" (v2.1.200), and removal of the mid-conversation system role on Sonnet 5 sessions (v2.1.201).
• v2.1.202–205 add advisory workflow sizing and OTel attributes, the fast single-pass /review split, MCP root updates, background/Agent View reliability, headless hook streaming, the full /doctor checkup and /checkup alias, Auto-mode transcript protection, and JSON Schema fixes.
• The v2.1.170 content remains valid for Fable 5 and Agent View, while the current Opus alias and default high-capability path move to Opus 5 in v2.1.219. Historical Opus 4.8 guidance is retained only where a version pin or compatibility path is explicit.
• Background sessions, dynamic workflows, and the command surface were rechecked against current docs.
• Fable-specific details include 30-day data retention, ZDR unavailability, always-on adaptive thinking, DISABLE_PROMPT_CACHING_FABLE, classifier fallback, and availability fallback chains.
• Fable 5 redeployment: suspended 2026-06-12 under US export controls, restored globally 2026-07-01 with an improved safety classifier; plan usage is up to 50% of weekly limits through 2026-07-07 then usage credits. Mythos 5 (no classifiers) is Project Glasswing invitation-only and not selectable via /model.
• Recent operating notes include /cd session relocation, --safe-mode, bundled skill/workflow disabling, self-hosted runner post-session hooks, and the v2.1.170 transcript persistence fix.

Source Baseline

• Claude Code Changelog: https://code.claude.com/docs/en/changelog
• Model configuration: https://code.claude.com/docs/en/model-config
• Commands: https://code.claude.com/docs/en/commands
• Subagents: https://code.claude.com/docs/en/sub-agents
• Hooks: https://code.claude.com/docs/en/hooks
• Sandboxing: https://code.claude.com/docs/en/sandboxing
• Agent View: https://code.claude.com/docs/en/agent-view
• Sonnet 5 announcement: https://www.anthropic.com/news/claude-sonnet-5
• Claude Fable 5.1 overview: https://platform.claude.com/docs/en/models/fable-5-1/overview
• What's new in Claude Fable 5.1: https://platform.claude.com/docs/en/models/fable-5-1/whats-new-fable-5-1
• Migrating to Claude Fable 5.1: https://platform.claude.com/docs/en/models/fable-5-1/migration-guide
• Fable 5.1 and Mythos 5.1 announcement: https://www.anthropic.com/claude-fable-and-mythos-5-1
• Fast mode: https://code.claude.com/docs/en/fast-mode
• Claude Fable 5 and Claude Mythos 5: https://platform.claude.com/docs/en/about-claude/models/introducing-claude-fable-5-and-claude-mythos-5
• Fable 5 redeployment statement: https://www.anthropic.com/news/redeploying-fable-5
• Claude models overview: https://platform.claude.com/docs/en/about-claude/models/overview
• Opus 4.8 announcement: https://www.anthropic.com/news/claude-opus-4-8
• npm package: https://www.npmjs.com/package/@anthropic-ai/claude-code

Residual Risk

The English locale now has multiple localized handbooks. Shared pages such as About and Graph have English UI labels, but deeper editorial polish should be handled as a separate content pass.