{"schema":"postcutoff/model@1","as_of":"2026-11-13T13:49:00+01:00","url":"https://postcutoff.com/m/claude-mythos-5-1/","md":"https://postcutoff.com/m/claude-mythos-5-1/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-mythos-5-1","name":"Claude Mythos 5.1","org":"Anthropic","family":"Claude 5","released":"2026-09-01","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":10,"output":50,"cache_read":0.25,"unit":"per 1M tokens (USD); Batch API 50% off","source":"https://platform.claude.com/docs/en/about-claude/pricing"},"price_line":"$10 in, $50 out per 1M tokens","access":[{"provider":"Anthropic API (Claude API)","model_id":"claude-mythos-5-1","endpoint":"https://api.anthropic.com/v1/messages","docs":"https://platform.claude.com/docs/en/models/mythos-5-1/overview"}],"capabilities":[{"name":"Frontier cyber-defense model","detail":"Offered only to Project Glasswing participants for defensive cybersecurity. It has the same capabilities as Fable 5.1, with safeguards that depend on the access program.","first":false,"discovered":"launch","source":"https://www.anthropic.com/claude-fable-and-mythos-5-1"},{"name":"Scientific discovery","detail":"Shares Fable 5.1's launch results, e.g. protein designs with about 10x higher binding affinity than competition winners.","first":false,"discovered":"launch","source":"https://www.anthropic.com/claude-fable-and-mythos-5-1"}],"entry":null,"notes":"Superseded on 2026-11-09 by Claude Mythos 5.2 (see claude-mythos-5-2). Invitation-only (Project Glasswing, defensive cybersecurity). Same capabilities/pricing as Claude Fable 5.1; not offered on Claude Platform on AWS. Cloud ids not listed publicly; contact Anthropic/AWS/Google account team. Successor to claude-mythos-5 and claude-mythos-preview (deprecated 2026-06-09).","verified":"2026-11-09","body_md":"Same model as Claude Fable 5.1 offered to approved Project Glasswing participants (https://anthropic.com/glasswing). Unlike Fable 5.1 it does not run the preserved-thinking history-editing check. If your org is not in Glasswing, use `claude-fable-5-1`.\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-mythos-5-1\",\"max_tokens\":16000,\"messages\":[{\"role\":\"user\",\"content\":\"Hello\"}]}'\n```\n\nSources:\n- Model page: https://platform.claude.com/docs/en/models/mythos-5-1/overview\n- Announcement: https://www.anthropic.com/claude-fable-and-mythos-5-1\n- Pricing: https://platform.claude.com/docs/en/about-claude/pricing\n- Models overview: https://platform.claude.com/docs/en/about-claude/models/overview\n- Deprecations: https://platform.claude.com/docs/en/about-claude/model-deprecations","page_url":"https://postcutoff.com/m/claude-mythos-5-1/","events_after":1795,"major_after":409,"historic_after":81,"missing_at_launch":191,"events_since_release":null,"you_url":"https://postcutoff.com/you/claude-mythos-5-1/","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"}}