AI models · Anthropic

Claude Fable 5.1

Anthropic recommends Claude Fable 5.1 for the most demanding reasoning and long tasks the AI runs on its own, when Opus 5.5 at higher effort is not enough. It improved a lot over Fable 5 on science and automation tasks. On common benchmarks, though, it scores below the cheaper Opus 5.5 and costs 2.5 times as much, so it is not the first pick for most people.

Strengths

  • Anthropic recommends it for the hardest reasoning and long autonomous tasks, when Opus 5.5 is not enough even at higher effort.
  • A big jump over Fable 5 in science and automation: 52.6% instead of 24.7% on Terminal-Bench-Science and 31.4% instead of 17.1% on AutomationBench (Anthropic's figures).
  • Reused input from the cache costs only $0.25 per million tokens. Anthropic estimates this saves about 25% on typical workloads and up to 45% on heavily agentic ones versus Fable 5.
  • Anthropic says safety filters step in more precisely than on Fable 5, about 60% less often per Claude Code session.

Weaknesses

  • The most expensive current Claude model: $10 input and $50 output per million tokens, 2.5 times the price of Opus 5.5.
  • It scores around 50 on the Artificial Analysis index, while the cheaper Opus 5.5 scores 58. It also trails on Terminal-Bench 4.0 (55.8% vs 66.4%).
  • It is slow: about 66 output tokens per second, 146th of 193 models measured by Artificial Analysis.
  • On Pro and Team Standard it is outside the plan limits and runs on credits only. On Max and Team Premium it can use at most half of the weekly limit.
  • Safety filters still reroute penetration testing, exploit writing and binary vulnerability scanning to Opus models. Forcing tool use through the API returns an error.

Best for

  • The hardest multi-step research
  • Long-running autonomous AI agents
  • Complex work with documents, spreadsheets and slides
  • Tasks where Opus 5.5 falls short

Not ideal for

  • Everyday chat
  • High-volume work where cost matters
  • Apps that need fast replies
  • Free plan users

How to use it in Europe

In Europe you get it in the Claude app with a Max plan or a premium Team or Enterprise seat, using at most half of your weekly limit. On Pro and Team Standard you can only use it with paid credits, and not at all on the free plan. Developers call it through the API. The direct API stores data in the US, with no EU region to choose. Anthropic says text from models released after August 2, 2026 carries an invisible watermark because of the EU AI Act.

What is coming

Confirmed by vendor According to Anthropic, this is the same model as Claude Fable 5.1, reserved for organizations verified through its programs. So far only a set of US organizations has it, with no date for wider access. When: no date yet, Anthropic promises wider access “as quickly as possible” →

Rumor, unconfirmed According to The Information, Anthropic is preparing a new model that should better understand what users actually want. Leaks on social media mention the name Fable 5.5, but it is unclear whether this is the same model. Anthropic has confirmed nothing. When: no date, leakers on X expected a release a week later in mid October 2026, which did not happen →

Price compared with similar models

0.3 1 3 10 30 Ministral 3 14B0.2 Llama 4 Scout0.24 Qwen3.8-Flash0.47 Claude Haiku 5.50.5 Nemotron 3.5 Super VL0.5 GPT-6 Luna0.5 GLM-5.3-Flash0.5 Mistral Small 40.6 Llama 4 Maverick0.65 Codestral 25.080.9 Beam 1.01 DeepSeek V4.1 Flash1.2 Muse Glimmer 30B1.2 Mistral Large 31.5 Qwen3.7-Plus1.6 Grok Build 0.12 Gemini 3.5 Flash-Lite2.5 Grok 4.32.5 Qwen3.8-27B3 Gemini 3.8 Flash3.75 DeepSeek V4 Pro3.96 Mistral Large 44.18 Muse Spark 1.34.25 Muse Spark Open4.25 GLM-5.34.4 GPT-6.1 Terra5 Qwen3.8-Max6 Qwen3.8-2.4T-A95B6 Grok 4.76 Mistral Medium 3.57.5 Claude Sonnet 5.510 Gemini 4 Carbon10 Gemini 4 Argon10 Kimi K3.1 Pro10 GPT-6.1 Sol10 Kimi K315 Claude Opus 5.520 Muse Wonder20 Claude Fable 5.150 GPT-6 Astra50
Output price in USD per 1M tokens (log scale). Lighter bars are open-weight models.

Benchmark results

BenchmarkScoreSource
Artificial Analysis Intelligence Index v5.0 (xhigh effort)50artificialanalysis.ai ↗, October 2026
Terminal-Bench 4.055.8%anthropic.com ↗ (vendor-reported), September 2026
Terminal-Bench-Science 0.152.6%anthropic.com ↗ (vendor-reported), September 2026
Humanity's Last Exam, no tools60.9%anthropic.com ↗ (vendor-reported), September 2026
OSWorld 2.0 partial77.9%anthropic.com ↗ (vendor-reported), September 2026

Benchmarks cover only a narrow slice of ability and vendors often report them at their best settings. Treat them as a rough guide.

More models from this vendor

  • Claude Opus 5.5: Anthropic's main model for demanding work, coding and long documents, and the one Anthropic recommends starting with.
  • Claude Sonnet 5.5: Claude's balanced model for everyday work and coding. It is faster than Opus 5.5 and costs half as much.
  • Claude Haiku 5.5: Claude's cheapest and fastest model, built for classification, data extraction and large volumes of simple tasks.

Similar models from other vendors

  • gpt-oss-120b (OpenAI): OpenAI's open model that a company can run on its own server when data must not leave its infrastructure.

Sources

Prices and models change often. The data comes from official vendor pricing pages and documentation, and every page shows when it was last checked. Before a larger purchase, confirm the price with the vendor.

← All AI models

Not sure which model fits your business?

I can help you pick a model and plan based on what you actually need, set it up safely for company data and train your team to use it well. Let’s start with an intro consultation.

See pricing [email protected]