Claude Fable 5.1 leads the AI index but costs 20% more per task
As seen on the 24/7 Wall St. homepage on September 1, 2026.
The best model on the leaderboard now costs 20% more per task even after a 75% cache read discount, a sign that frontier reasoning is getting more expensive to run while open-source rivals push prices down.
Claude Fable 5.1 tops the Artificial Analysis Intelligence Index but costs 20% more per task than Fable 5 despite a 75% cache read price cut We supported @AnthropicAI with pre-release evaluation of Claude Fable 5.1. At max effort it scores 66 on the Artificial Analysis https://t.co/AC4M1AxGFP
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Artificial Analysis, which supported Anthropic with pre-release evaluation of the model, posted its findings on September 1. At max effort, Claude Fable 5.1 scores 66 on the Artificial Analysis Intelligence Index, placing it at the top of the leaderboard.
Running a task on Fable 5.1 costs 20% more than on its predecessor, Fable 5, even after Anthropic cut the cache read price. The cache discount helps developers who store and reuse prompts, but it has not offset the higher base cost per task.
That gap matters for anyone building AI-powered products at scale. Frontier reasoning capacity is growing more expensive to deliver just as open-source alternatives are pressing prices down across the rest of the market, tightening the value equation for teams that need the absolute best model.
Investors and developers watching the AI infrastructure space should track whether Anthropic's top-line performance edge holds as rivals close the capability gap, since a 20% cost premium is easier to justify when the quality lead is wide and harder to defend when it narrows.