{"schema":"postcutoff/model@1","as_of":"2026-11-09T21:13:00+01:00","url":"https://postcutoff.com/m/claude-fable-5-2/","md":"https://postcutoff.com/m/claude-fable-5-2/index.md","disclosure":{"written_by":"AI agents (Claude Opus 5.5 in Claude Code)","editor":"human editor","policy":"https://postcutoff.com/about/"},"license":null,"id":"claude-fable-5-2","name":"Claude Fable 5.2","org":"Anthropic","family":"Claude 5","released":"2026-11-09","status":"current","type":"reasoning-llm","modality_in":["text","image","pdf"],"modality_out":["text"],"open_weights":false,"model_license":"proprietary","context_window":1000000,"max_output":128000,"knowledge_cutoff":"2026-06","pricing":{"input":8,"output":40,"cache_write_5m":10,"cache_write_1h":16,"cache_read":0.2,"unit":"per 1M tokens (USD); fast mode (up to 2.5x faster output) $16 input / $80 output","source":"https://platform.claude.com/docs/en/about-claude/pricing"},"price_line":"$8 in, $40 out per 1M tokens","access":[{"provider":"Anthropic API (Claude API)","model_id":"claude-fable-5-2","endpoint":"https://api.anthropic.com/v1/messages","docs":"https://platform.claude.com/docs/en/models/fable-5-2/overview"},{"provider":"AWS Bedrock","model_id":"anthropic.claude-fable-5-2","docs":"https://platform.claude.com/docs/en/build-with-claude/claude-in-amazon-bedrock"},{"provider":"Google Cloud (Claude Models on Google Cloud)","model_id":"claude-fable-5-2","docs":"https://platform.claude.com/docs/en/build-with-claude/claude-on-vertex-ai"},{"provider":"Microsoft Foundry (Azure)","model_id":"claude-fable-5-2","docs":"https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry"},{"provider":"OpenRouter","model_id":"anthropic/claude-fable-5.2","url":"https://openrouter.ai/anthropic/claude-fable-5.2"},{"provider":"Web app (all paid plans), Claude Code","url":"https://claude.ai"}],"capabilities":[{"name":"Top agentic-coding score at launch","detail":"FrontierCode 2.0: 49.1% at Xhigh effort, the highest of any released model Anthropic tested (Opus 5.5 45.5%, GPT-6 Astra 42.8%, Gemini 4 Carbon 41.1%); at High effort it matches Opus 5.5's best for about half the cost per task. Vendor numbers.","first":false,"discovered":"launch","source":"https://www.anthropic.com/claude-fable-and-mythos-5-2"},{"name":"Fermat's Last Theorem formalized in 30 hours","detail":"About 1,000 Fable 5.2 agents fully formalized FLT in Lean in 30 hours with minimal human intervention (the first formalization by an unreleased Claude took 11 days); Opus 5.5 with the same setup reached 26% in 18 hours.","first":true,"discovered":"launch","source":"https://www.anthropic.com/research/formalizing-fermats-last-theorem"},{"name":"Robot control without robotics training","detail":"RoboDojo Sim (simulated two-arm robot from camera images): 64.9% at Max effort, versus 39.4% for Opus 5.5, 34.2% Gemini 4 Argon and 29.8% GPT-6 Astra in Anthropic's runs; beats most purpose-built robot-control systems on the public board.","first":false,"discovered":"launch","source":"https://robodojo-benchmark.com/"},{"name":"Hardware design end to end","detail":"From a one-paragraph prompt it specified, sourced parts for, routed four-layer boards and wrote firmware for three devices (voice hub, USB speakerphone, handheld pet) built with Diode; all worked without electrical changes. BenchCAD 2.1: 83.5 vs 65.3 for Opus 5.5.","first":false,"discovered":"launch","source":"https://www.anthropic.com/news/model-hardware-standard-research-preview"},{"name":"Open physics problems","detail":"Solved two open problems on holographic black holes (Hawking–Page transition at weak coupling is first order; the exact limit of the modular bootstrap slope), posted on Hexagon as 2611.00175 and 2611.00174.","first":false,"discovered":"launch","source":"https://hexagonmath.org/2611.00175v1"},{"name":"Fewer safety-classifier blocks","detail":"About 55% fewer blocks than Fable 5.1 in early testing (60% fewer in cyber, 40% in biology); blocked cyber queries are answered by Opus 4.8 and biology ones by Opus 5.","first":false,"discovered":"launch","source":"https://www.anthropic.com/claude-fable-and-mythos-5-2"}],"entry":"2026-11-09-claude-fable-5-2-mythos-5-2","notes":"Same underlying model as Claude Mythos 5.2 (Mythos without the cyber/biology classifiers, for verified organizations). Up to 30% faster output than Fable 5.1; optional fast mode up to 2.5x. Default effort: high on the API, medium in Claude apps and Claude Code. Retirement not before 2027-11-09. Anthropic still recommends Opus 5.5 as the starting point for most coding and knowledge work. AI-R&D-specific capabilities (kernel optimization, LLM architecture work) were deliberately held at about Opus 5.5 level during training; transparent fallbacks to Opus 5 on some of those topics. Strongest anti-distillation protections; preserved thinking now applies to all accounts. 30-day retention for safety monitoring unless the customer uses Enterprise Frontier Safeguards (ZDR-compatible).","verified":"2026-11-09","body_md":"Anthropic's strongest widely released model from 9 November 2026, replacing Fable 5.1 at a lower price ($8/$40 instead of $10/$50). Best for long-horizon, open-ended technical work and as an Advisor or Orchestrator for smaller Claude models. Handle `stop_reason: \"refusal\"` from the safety classifiers.\n\nLaunch benchmarks (Anthropic, safeguards on, highest effort unless noted): FrontierSWE v2 69.9%, AutomationBench 51.4%, Terminal-Bench-Science 0.1 74.6%, OSWorld 2.1 (offline, partial) 89.3%, WANDR 82.1%, Remote Labor Index 41.3%, Humanity's Last Exam (tools) 74.2%, Chartography 73.4%, AA-Briefcase 66.1% rubric / 1785 Elo. Independent leaderboards had not published results on launch day.\n\n```bash\ncurl https://api.anthropic.com/v1/messages \\\n -H \"x-api-key: $ANTHROPIC_API_KEY\" -H \"anthropic-version: 2023-06-01\" -H \"content-type: application/json\" \\\n -d '{\"model\":\"claude-fable-5-2\",\"max_tokens\":16000,\"messages\":[{\"role\":\"user\",\"content\":\"Hello\"}]}'\n```","page_url":"https://postcutoff.com/m/claude-fable-5-2/","events_after":1712,"major_after":388,"historic_after":79,"missing_at_launch":1709,"events_since_release":null,"you_url":"https://postcutoff.com/you/claude-fable-5-2/","briefings":{"xs":"https://postcutoff.com/briefings/cutoff-2026-06-xs.md","s":"https://postcutoff.com/briefings/cutoff-2026-06-s.md","m":"https://postcutoff.com/briefings/cutoff-2026-06-m.md","full":"https://postcutoff.com/briefings/cutoff-2026-06.md"}}