METR Report Reveals Anthropic Internal Codenames: Model 3 Trained Aug-Sept 2026
haider1 · x · 2026-11-07
METR's methodology section lists Anthropic internal-only model codenames: Unreleased 2022, Model 2 (trained July 2026), Model 3 (Aug-Sept 2026, highlighted), and Model 4 (Sept-Oct 2026), with the future-model forecast redacted. haider1 speculates Opus 5.5 could be Model 3, and that Fable 5.5 has been ready for a while — a big leap over Mythos/Fable 5, meaning the true capability gap is smaller than a direct Mythos 5 comparison suggests.
Related event: METR report leaks Anthropic internal model codenames through Model 4(4 posts)→
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