Anthropic's latest Fable 5.1 model jumps to the top of LLM leaderboards

Anthropic launched a new model on September 1 called Claude Fable 5.1. 

The model immediately claimed the number one spot on Artificial Analysis’s intelligence leaderboard with a score of 66 on the site’s index, dethroning Opus 5 in the process.

Fable 5.1 and Opus 5 sit atop the leaderboard

Artificial Analysis ranks over 250 language models on price, speed, and intelligence. It now ranks two Fable 5.1 iterations first and second on the table. The site scores the “max with fallback” at 66, while scoring the “xhigh with fallback” at 65. 

Both tower above former leader Claude Opus 5 with a score of 63 in its max and xhigh modes.

That means Anthropic has the top four spots on a leaderboard that has models from top AI labs like OpenAI, Google, SpaceXAI, Alibaba, and DeepSeek. The closest to any Anthropic model is  OpenAI’s GPT-5.6 Sol at max mode and SpaceXAI’s Grok 4.6, both scoring 61. 

The ranking comes from an independent party, giving it more validity than a lab’s own charts.  

Where the coding and research scores landed 

Anthropic internal numbers tell a similar story, even though they ought to be read as vendor-reported. Anthropic’s reporting ranks Fable 5.1 at 52.6% on Terminal-Bench-Science 0.1, which is a test of agentic scientific research. That figure is double that of Fable 5’s 24.7% and miles ahead of the 29% and 22.4% of Opus 5 and GPT-5.6 Sol, respectively.  

Fable  5.1 scores 55.8% on the Terminal-Bench 4.0 coding benchmark, higher than Fable 5’s score of 42.0%.

The selling point is the ability of this new model to do work that runs for hours. Millennium told Anthropic that Fable 5.1 was able to trace a rare crash in its system to a bug that had proved too stubborn for its engineers for the past four to five years. 

Browserbase said the new model completed 82% of tasks on its hardest browser-agent test, compared to 74% for Opus 5.

A 75% cut to cache-read pricing                                      

There was no change in price, though. Fable 5.1 maintains Fable 5’s rates of $10 per million input tokens and $50 per million output tokens, way more than Opus 5, which costs $5 and $25, and Sonnet 5, going at $2 and $10.

The change occurs in the price of cached context. Anthropic reduced the cache-read price to $0.25 per million tokens, from $1.00, a 75% cut. 

Anthropic estimates that the average workload will become 25% cheaper, while heavily agentic workloads will become 45% cheaper. This is as a result of agents’ ability to reread the same code, instructions, and conversation history.

Same model, two safeguard tiers

Anthropic launched a second name with Fable 5.1: Claude Mythos 5.1. They are basically the same models, but with separate safeguards. Fable 5.1 is available to the general public, but Mythos 5.1 is available only to vetted cybersecurity and life-sciences groups via Anthropic’s Project Glasswing. 

That split comes after a tough period for Anthropic’s safety testing. As Cryptopolitan reported, Anthropic put a pause on external cybersecurity evaluations on July 23. This came after Claude got to real systems during tests meant to be sandboxed. 

The company resumed external cybersecurity evaluations once it was able to add appropriate containment measures.

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