Claude Fable 5.1 tops Intelligence Index, costs 20% more per task

Anthropic's Claude Fable 5.1, released September 1, 2026, tops the Artificial Analysis Intelligence Index with a score of 66, beating 192 competing models, but costs roughly 20% more per task than its predecessor, averaging $3.69 per task versus $3.08–$3.25 for Fable 5. Despite a 75% cut in cache read prices to $0.25 per million tokens, the model's verbosity on complex tasks drives up costs, with output tokens still priced at $50 per million.

Photo: Photo: Rostislav Uzunov / Pexels / Pexels Claude Fable 5.1 tops Intelligence Index, costs 20% more per task Anthropic's newest model scores highest among 192 AI models but generates bigger bills thanks to verbose outputs on complex tasks Anthropic’s Claude Fable 5.1 just claimed the top spot on the Artificial Analysis Intelligence Index with a score of 66, beating out more than 192 competing models. That’s the good news. The less convenient news: it costs roughly 20% more per task than its predecessor, despite a massive 75% cut to cache read prices. The model, released on September 1, 2026, averages $3.69 per task on the Intelligence Index. Fable 5, which launched in June, ran between $3.08 and $3.25 per task. The pricing paradox On paper, Fable 5.1’s pricing looks identical to its predecessor. Input tokens still cost $10 per million. Output tokens still cost $50 per million. Those numbers haven’t budged since Fable 5 debuted on June 9. Where Anthropic did cut prices is on cache reads, slashing them from $1 per million tokens down to $0.25 per million tokens. That 75% reduction is genuinely meaningful for users who repeatedly query large datasets or maintain persistent context across sessions. But the per-task cost increase tells a different story. Fable 5.1’s enhanced capabilities in long-horizon agentic coding and multi-step research mean the model tends to generate significantly more output when tackling complex problems. We’re talking up to 140 million output tokens on demanding workloads. At $50 per million output tokens, that verbosity adds up fast. What actually improved Fable 5.1’s Intelligence Index score of 66 represents a notable jump from Fable 5, which fluctuated between 60 and 64.9 across its lifespan. The improvements center on two areas Anthropic has been investing heavily in: long-horizon agentic coding and multi-step research capabilities. The 1 million-token context window supports these complex, multi-day workflows by allowing the model to hold enormous amounts of information in working memory simultaneously. Fable 5.1 also outperforms Claude Opus 5.1, Anthropic’s other premium model line. Opus 5 launched in July 2026, just a month after Fable 5, as part of what has become an aggressive release cadence from the company. Three major model launches in roughly three months suggests Anthropic is running hot on its development pipeline. The competitive landscape Anthropic’s tiered availability strategy for Fable 5.1, spanning Pro, Max, Team, and Enterprise tiers, positions the model squarely in the premium segment. The 75% cache read discount pulls in one direction, making the model cheaper for repetitive, data-heavy workloads. The higher per-task cost on complex reasoning pulls in the other direction, making it more expensive precisely when users need the model’s best capabilities. For enterprise buyers evaluating AI budgets, this tradeoff requires careful consideration. A team running mostly cache-heavy workloads, think large document analysis or persistent knowledge bases, could see meaningful savings. A team running novel, complex reasoning tasks could see costs climb by 20% or more compared to what they were spending on Fable 5. Disclosure: This article was edited by Editorial Team. For more information on how we create and review content, see our Editorial Policy https://cryptobriefing.com/editorial-policy/ .