AI news story

Anthropic Releases Claude Fable 5.1 and Claude Mythos 5.1: 52.6% on Terminal-Bench-Science and 75% Cheaper Cache Reads

Anthropic has released Claude Fable 5.1 and Claude Mythos 5.1, the same model behind two different safeguard layers. Fable 5.1 is generally available on the Claude API, AWS, Google Cloud, and Microsoft Foundry; Mythos 5.1 remains restricted to vetted

  • LLMs
  • Source: MarkTechPost
  • Published: 2026-09-01
  • Signal score: 4
  • 74 sources

Editor's take

Anthropic has introduced updated versions of its Claude models, Fable 5.1 and Mythos 5.1, with Fable now accessible via public APIs and cloud platforms, while Mythos remains restricted.

The significance lies in Fable 5.1's reported 52.6% score on the Terminal-Bench-Science benchmark, indicating improved scientific reasoning capabilities, and a 75% reduction in cache read costs. This move positions Anthropic to compete more effectively with models like OpenAI's GPT-4 in specialized domains, while the tiered release strategy suggests a controlled approach to deploying advanced, potentially more sensitive, AI functionalities.

Future developments to monitor include the performance of Fable 5.1 on a wider array of complex reasoning tasks and the specific criteria for vetting Mythos 5.1 access. The cost savings on cache reads could also signal a broader trend in LLM infrastructure optimization, impacting overall deployment economics for AI services.

Signal score: 4

This event was corroborated by 74 independent sources. The signal score weighs cross-source corroboration, recency, source weight and topic salience. How we rank stories.

Original reporting

This story summarises reporting published by MarkTechPost. Read the original article at MarkTechPost.

More LLMs stories

  1. Seattle Times and Newsday sue OpenAI and Microsoft for infringement

    The Verge · 2026-09-06

    The Seattle Times and Newsday are just the latest plaintiffs to take OpenAI to court, alleging copyright infringement.

  2. Supporting independent journalism in Ukraine

    OpenAI Blog · 2026-09-07

    OpenAI, AIRPPU and WAN-IFRA launch an AI program to help Ukrainian news organizations strengthen innovation, resilience, and independent journalism.

  3. The Sycophancy Trap: How a 0.7B Parameter Model Fooled a Frontier LLM into Believing It Was a Peer

    Towards AI · 2026-09-07

    A diminutive 0.7 billion parameter model successfully deceived a significantly larger, frontier large language model (LLM) into believing they were peers

  4. Does Claude Fable 5.1 Check its Own Work? I Broke 10 Repos to See

    Towards AI · 2026-09-07

    One seeded defect per repository, twenty runs, and not a single claim the tests disagreed withContinue reading on Towards AI »

  5. Every Benchmark You Trust Is Probably in the Training Data by Now

    Towards AI · 2026-09-06

    OpenAI admitted GSM-8K’s training set went into GPT’s training data.

  6. Authors push back as publishers and agents make claims on Anthropic settlement

    TechCrunch · 2026-09-06

    Authors say publishers seem to be claiming more than their fair share of settlement payments.