Anthropic has released Claude Fable 5.2 and Claude Mythos 5.2, pairing record-high artificial intelligence benchmark results with a 20% API cost reduction to $8 per million input tokens and $40 per million output tokens. Built on a shared architecture, Fable 5.2 targets general enterprise software development and research, while Mythos 5.2 is reserved for vetted cyber and life-sciences researchers. The release intensifies competition with OpenAI and Google ahead of Anthropic's planned IPO.
Model launch and dual-tier safety structure
- ▪Claude Fable 5.2 and Claude Mythos 5.2 are built on the same underlying model, but Fable 5.2 includes classifiers that block high-risk cybersecurity and research biology tasks
- ▪Anthropic made Claude Fable 5.2 available on paid Claude plans, Claude Code, the Claude Platform, Amazon Web Services, Google Cloud, and Microsoft Azure
- ▪Anthropic launched Claude Fable 5.2 and Claude Mythos 5.2 on November 9, 2026, targeting coding, reasoning, and AI agent tasks
Demonstrated capabilities in math and OS development
- ▪Anthropic said during pre-release testing, 1,000 Fable 5.2 agents formalized the proof of Fermat's Last Theorem in Lean in 30 hours, compared to 26% completion in 18 hours by Opus 5.5
- ▪In a pre-release project, 1,000 Fable 5.2 subagents built an operating system over eight days that boots on a laptop, offers network access, and includes a Claude sidebar
Benchmark performance on coding and automation
- ▪Anthropic said Claude Fable 5.2 scored 51.4% at Max effort on Zapier's AutomationBench business automation test, behind Gemini 4 Carbon's score of 53.9%
- ▪Anthropic said Claude Fable 5.2 scored 49.1% at Xhigh effort on the FrontierCode 2.0 agentic coding benchmark, leading GPT-6 Astra at 42.8% and Gemini 4 Carbon at 41.1%
- ▪Anthropic said Claude Fable 5.2 scored 69.9% on FrontierSWE v2, outperforming GPT-6 Astra at 65.5% and Gemini 4 Carbon at 61.2%
API pricing and output speed improvements
- ▪Anthropic's Batch API pricing for Fable 5.2 and Mythos 5.2 halves input and output rates to $4 and $20 per million tokens, respectively
- ▪Anthropic said Claude Fable 5.2 and Mythos 5.2 generate token outputs up to 30% faster than Fable 5.1 and Mythos 5.1, their predecessors
- ▪Anthropic introduced an optional Fast mode for Fable 5.2 and Mythos 5.2 that increases token generation speed by up to 2.5 times at $16 input and $80 output per million tokens
- ▪Anthropic priced Claude Fable 5.2 and Claude Mythos 5.2 at $8 per million uncached input tokens and $40 per million output tokens, representing a 20% cost reduction over Fable 5.1 and Mythos 5.1, their predecessors
Access controls and fallbacks for restricted domains
- ▪When Fable 5.2 blocks a request due to safety guardrails, requests fall back to Opus 4.8 for cybersecurity and Opus 5 for biology queries
- ▪Anthropic restricted access to Claude Mythos 5.2 to vetted organizations through its Cyber Verification Program and Life Sciences Verification Program
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