# Anthropic launches Claude Fable 5.1 — stronger benchmarks and cheaper long-running agents

> Claude Fable 5.1 delivers major gains in agentic research, coding and business workflows, outperforming Fable 5 and Opus 5 across Anthropic’s published tests. Its base API pricing remains unchanged, but cheaper cache reads could cut typical costs by around 25%—positioning it as the premium choice for demanding, long-running tasks.
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> OpenCheese AI · 2026.09.01 · Web page: https://opencheese.dev/blog/anthropic-launches-claude-fable-5-1-stronger-benchmarks-and-cheaper-long-running-agents

Anthropic launches Claude Fable 5.1 — stronger benchmarks and cheaper long-running agents

Anthropic has released Claude Fable 5.1, its new flagship model for difficult reasoning, coding, research and long-horizon agentic work. It is available now across Claude’s platforms and via the API, including AWS, Google Cloud and Microsoft Azure.

A quick look at Anthropic’s published tests (Fable 5.1 / Fable 5 / Opus 5):

• Terminal-Bench-Science 0.1: 52.6% / 24.7% / 29.0%
• Terminal-Bench 4.0: 55.8% / 42.0% / 52.3%
• GDPval-AA v2: 1853 / 1723 / 1824
• AutomationBench: 31.4% / 17.1% / 26.9%
• CursorBench 3.2: 73.4% / 70.5% / 70.0%

The biggest leap is in agentic scientific research: Fable 5.1 more than doubles Fable 5’s result. It also leads Opus 5 in all five examples above. These are Anthropic’s own evaluations, and the company notes that production safeguards and fallback behavior can affect some scores.

The model keeps Fable 5’s base API price—$10 per million input tokens and $50 per million output tokens—but cached reads are now 75% cheaper at $0.25 per million. Anthropic estimates roughly 25% lower costs for typical workloads and up to 45% for context-heavy agentic tasks.

The trade-off: Opus 5 remains half the base price at $5/$25 and is still Anthropic’s recommended starting point for most workloads. Fable 5.1 is the premium option when maximum reasoning and sustained autonomous work matter more than price.

Source: [Anthropic’s announcement](https://www.anthropic.com/claude-fable-and-mythos-5-1) and [model documentation](https://platform.claude.com/docs/en/models/fable-5-1/overview).

## Related posts

- 2026.09.22 · [Claude Opus 5.5 Is Now Available on OpenCheese](https://opencheese.dev/blog/claude-opus-5-5-is-now-available-on-opencheese.md): Anthropic’s strongest Opus model yet is now available on OpenCheese. Claude Opus 5.5 delivers major improvements in coding, agents, professional work, vision, and efficiency.
- 2026.11.10 · [Claude Fable 5.2 vs Opus 5.5, twice the price per token and sometimes half the price per task](https://opencheese.dev/blog/claude-fable-5-2-vs-opus-5-5-price-per-token-and-per-task.md): Claude Fable 5.2 costs $8 and $40 per million tokens, double Opus 5.5. On some benchmarks it reaches Opus's best score at a lower effort for half the money, on others it costs 2.6 times as much per task. Every number is checked against Anthropic's docs, the system card and independent leaderboards.
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