{ "story_id": "e96c670c90c451a01ec13ec0e99206a7", "desk": "drm3", "revision": 2, "published_at": "2026-09-02T14:52:19.000Z", "content_hash": "2076bca8a9e1a542602407181feaae1ac33ba8158a63ed536cb9d03010755d21", "hash_basis": "sha256 over `headline\\ndek\\nprose`, plus `\\n` + the canonical citations JSON when any source is placed, plus `\\n#blog` for blogs", "basis": { "headline": "Anthropic Launches Claude Fable 5.1 to Block AI Distillation", "dek": "Anthropic releases Claude Fable 5.1 with new security locks to prevent rivals from distilling its reasoning.", "prose": "Anthropic released Claude Fable 5.1 and Claude Mythos 5.1 on September 1, 2026, describing them as the world's most advanced models for coding and knowledge work. [^1]\n\nAnthropic stated that new API accounts opened on or after August 31 can no longer manually edit Claude's prior context in multi-turn conversations while preserving the transcript of Claude's prior thinking. [^2]\n\nAnthropic reported that over 16 million Claude exchanges were traced to distillation campaigns run through roughly 24,000 fake accounts, with Moonshot AI accounting for 3.4 million exchanges. [^3]\n\nOn Terminal-Bench 4.0, Claude Fable 5.1 achieved 55.8%, surpassing Opus 5 at 52.3% and OpenAI's GPT-5.6 Sol at 37.3%. [^4]\n\nAnthropic claimed on September 1, 2026 that Claude Fable 5.1 and Claude Mythos 5.1 are the 'world's most advanced models for coding and knowledge work.' [^5]\n\nAnthropic said on September 1, 2026 that Claude Code users should see around 60 percent fewer cybersecurity false positives with Claude Fable 5.1's improved safeguards. [^6]\n\nAnthropic said on September 1, 2026 that Claude Fable 5.1 costs approximately 25 percent less than Fable 5 for typical workloads and up to 45 percent for highly agentic work due to reduced cache-read pricing, while base pricing remains the same. [^7]\n\nAnthropic stated that Fable 5.1 would cost an estimated 25% less than Fable 5 for typical token-billed workloads, with savings up to 45% for highly agentic work. [^8]\n\nAnthropic will add a watermark to outputs of models released after August 2, 2026, per the EU AI Act Code of Practice, and is rolling out a watermark detection API in private preview. [^9]\n\nAnthropic announced the release directly, positioning Fable 5.1 specifically around autonomous, multi-step work and Mythos 5.1 as the paired release for knowledge work. [^10]\n\nAnthropic kept list pricing for Fable 5.1 at $10 per million tokens for input, $50 per million tokens for output, and $12.5 per million tokens for cache write. [^11]\n\nAnthropic claims that Claude Mythos 5.1 reduces false positive security blocks by 60 percent compared to its predecessor while analyzing vulnerabilities without generating exploits. [^12]", "cited": "[{\"statement\":\"Anthropic released Claude Fable 5.1 and Claude Mythos 5.1 on September 1, 2026, describing them as the world's most advanced models for coding and knowledge work.\",\"source\":\"beincrypto.com\",\"instrument\":\"News\",\"claim_key\":null,\"published_at\":\"2026-09-01T18:24:03.000Z\",\"publisher_count\":1,\"sources\":[\"beincrypto.com\"]},{\"statement\":\"Anthropic stated that new API accounts opened on or after August 31 can no longer manually edit Claude's prior context in multi-turn conversations while preserving the transcript of Claude's prior thinking.\",\"source\":\"beincrypto.com\",\"instrument\":\"News\",\"claim_key\":null,\"published_at\":\"2026-09-01T18:24:03.000Z\",\"publisher_count\":1,\"sources\":[\"beincrypto.com\"]},{\"statement\":\"Anthropic reported that over 16 million Claude exchanges were traced to distillation campaigns run through roughly 24,000 fake accounts, with Moonshot AI accounting for 3.4 million 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will add a watermark to outputs of models released after August 2, 2026, per the EU AI Act Code of Practice, and is rolling out a watermark detection API in private preview.\",\"source\":\"The Hindu\",\"instrument\":\"News\",\"claim_key\":null,\"published_at\":\"2026-09-02T08:59:03.000Z\",\"publisher_count\":1,\"sources\":[\"The Hindu\"]},{\"statement\":\"Anthropic announced the release directly, positioning Fable 5.1 specifically around autonomous, multi-step work and Mythos 5.1 as the paired release for knowledge work.\",\"source\":\"latent.space\",\"instrument\":\"News\",\"claim_key\":null,\"published_at\":\"2026-09-02T07:46:08.000Z\",\"publisher_count\":1,\"sources\":[\"latent.space\"]},{\"statement\":\"Anthropic kept list pricing for Fable 5.1 at $10 per million tokens for input, $50 per million tokens for output, and $12.5 per million tokens for cache 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