Anthropic Latest Fable 5.2 is a Crippled Model 3 Early and They Have Model 4 Internally

Model 4 is an internal, unreleased Anthropic AI model identified in METR's October 2026 assessment. It finished training between September and October 2026 and was the first model in METR's test set to score above 50% on all 15 benchmarks evaluated.

The Fable 5.2 Modle is Model 3 Early.

Has Anthropic confirmed Model 4 publicly?

No. Model 4, along with internal predecessors METR calls Model 2 and Model 3, comes from METR's independent report rather than an Anthropic product announcement. Anthropic gave METR access to internal data but redacted significant portions of the underlying evidence before the report was published.

What does METR mean by "AI R&D acceleration"?

It refers to AI systems helping speed up the process of researching and building better AI, as opposed to speedups from simply buying more computing power. METR estimated that around 80% of Anthropic's recent capability gains come from this kind of AI-assisted research rather than compute growth, though it stressed this estimate carries real uncertainty.

Is this the same thing as recursive self-improvement?

It's an early form of recursive self improvement, by the definition Google DeepMind CEO Demis Hassabis has used publicly. AI making researchers several times more productive while humans remain in the loop reviewing and directing the work. A more concerning "closed loop" version, where AI does the research without human review, has not been confirmed in METR's findings, though the report notes early signs of more autonomous AI contributions appearing.