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Claude Fable 5.2 Sets a New Epoch Capabilities Index Record

Epoch AI · X· @EpochAIResearch·· 3 days ago

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Epoch AI
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reports a new record Claude Fable 5.2’s score on the Epoch Capabilities Index
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Claude Fable 5.2 sets a new record on the Epoch Capabilities Index (ECI) at 174.

What happened

Epoch AI reports that Claude Fable 5.2 scored 174 on the Epoch Capabilities Index, above the previous high of 169 set by GPT-6 Astra. The score is above what the pre-Astra trend for reasoning models would have predicted. Epoch AI says the result is based on pre-launch testing using only its own benchmarks, and the index may change as more results become available.

Read next

See the full storyAnthropic Releases Claude Fable 5.2 and Mythos 5.2 with Lower API Prices
Article

Claude Fable 5.2 sets a new record on the Epoch Capabilities Index (ECI) at 174. The previous high was GPT-6 Astra’s 169. Fable 5.2’s score is above what the pre-Astra trend for reasoning models would have predicted.

This is notable given recent discussion of AI contributions to AI R&D, and we hope to release more work in this area soon.

This is based on testing we did prior to launch using only our own benchmarks. The ECI is continually updated as more benchmark results become available, and may change in the future.

The story so far

Anthropic released Claude Fable 5.2 and Claude Mythos 5.2, lowering API prices to $8 per million input tokens and $40 per million output tokens, from $10 and $50. Anthropic says both models improve coding, reasoning, and vision, and that Fable produces responses faster than version 5.1. Fable is available to paid users with safeguards for risky cybersecurity and biology tasks; Mythos is limited to organizations approved through Anthropic’s verification programs. The launch reports cite strong benchmark results, including Fable’s first-place score on Artificial Analysis’ Intelligence Index v5 at its highest compute tier. Those figures come from the named benchmark evaluations; Anthropic’s prerelease examples also include software migrations, electronic devices, and physics problems. TechCrunch reports that an optional faster serving mode costs twice as much, while the lower API prices apply to standard use.

Anthropic / ClaudeReasoningBenchmarks