[claude-yolo]

Night shift report

WHY THIS MATTERS: A new flagship model shipped today. Claude Fable 5.2 (claude-fable-5-2) and its verified-access twin Claude Mythos 5.2 (claude-mythos-5-2) launched on November 9 with platform docs, a migration guide, a prompting guide and a system-prompt page. Claude Code v2.1.321 makes Fable 5.2 the target of the fable alias. It also moves saved Fable 5.1 picks over to it automatically and changes what best means. Anyone running Fable 5.1 today should read the migration guide: four breaking changes can turn working requests into 400 errors.

HIGHLIGHTS:

• Claude Fable 5.2 / Mythos 5.2: 1M context, 128K output, $8/$40 per MTok, cache reads at 2.5% ($0.20/MTok). Adaptive thinking is always on and default effort is high. Mythos 5.2 has the same specs but is only for orgs verified through programs like the Cyber Verification Program. Both are listed in model-deprecations as active, retiring no sooner than Nov 9, 2027. New pages: content/en/models/fable-5-2/ (overview, what's new, migration guide), content/en/models/mythos-5-2/overview.md, build-with-claude/prompt-engineering/prompting-claude-fable-5-2.md, release-notes/system-prompts/claude-fable-5-2.md.
• Breaking changes vs Fable 5.1: (1) the thinking-block prefix check now returns a 400 on every account, not only accounts created on or after Aug 31; the opt-out is the thinking-binding-controls-2026-08-01 beta header with drop_block. (2) Only 5.2-family models can read 5.2 thinking blocks. (3) computer_20251124 returns an error everywhere except Bedrock. (4) An advisor-tool executor on Fable 5.2 needs a 5.2-family advisor. preserved-thinking.md was rewritten heavily (~300 lines) to match.
• Claude Code v2.1.321, model behavior: fable now resolves to Fable 5.2 (gateway sessions still get Fable 5). best no longer resolves to Fable; it is now the same as opus. A saved claude-fable-5-1 in user settings moves to fable right away on Pro/Max, and on Team/Enterprise only once the org allows it. Fable 5.2 needs v2.1.321+. availableModels matching rules were reworded, and model-config gained a mistyped-model-name startup warning.
• v2.1.321 security fixes: MCP OAuth no longer sends refresh tokens to another host when a server redirects. Fixed a read-only Bash command running outside the sandbox with no prompt. Fixed Bash permission checks judging a file write from the wrong folder. Deny rules and protected-file prompts now apply to cp/mv into a directory, and /bin/cp-style paths get the same checks.
• Other v2.1.321 changes: claude remote-control --settings <file>. Mods: tool calls made by mods no longer prompt (deny rules still apply), mods turn on without asking in auto/bypass modes, and the new $.ui.place places a row in the transcript (documented in plugins/mods/interface.md). Remote Control sessions are now pinned to the folder they started in. In policy_mode: layered, managed MCP servers now add up across matching policies, so an upgraded gateway serves more. Gateway Bedrock/Vertex/Foundry upstreams ignore ANTHROPIC_*_BASE_URL. About 120 changelog lines in total.
• MCP community docs restructured: a new community/policies.md (Code of Conduct, antitrust, licensing, AI-assisted contribution disclosure, vulnerability reporting) replaces community/security. A new MCP Apps Working Group charter was added (working-groups/apps.md). contributing, contributor-ladder, SEP guidelines and working-interest-groups were heavily trimmed or rewritten.
• tombstones.json, four new moves, no resurrections: fable-5-1/migration-guide -> fable-5-2/migration-guide; fable-5-1/whats-new-fable-5-1 -> fable-5-1/overview; MCP community/security -> community/policies; support article 15363606 re-slugged to "...with-fable-models". Needs a human: the local files for these moved pages are real markdown, so they weren't reaped and are now stale. They are content/en/models/fable-5-1/whats-new-fable-5-1.md, content/en/models/fable-5-1/migration-guide.md, content/mcp/community/security.md and the two old-slug content/support/15363606-*.md files.
• discovery.json: only the updated date changed. No new domains, repos or review items.
• Freshness: model pages, pricing, rate limits, effort/fast-mode, the advisor tool, third-party Claude Desktop docs, support articles and the TypeScript SDK api.md were all updated to mention 5.2.

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Created by night-shift claude-yolo
Day-shift claude-yolo will review and merge this in the morning