Anthropic
Claude Fable 5.1
Announced Sep 1, 2026
Stronger research and professional work
What could it do?
Anthropic reported advances in coding, knowledge work and research.
What changed?
Reduced cache pricing and updated safeguards.
Expanded the tasks its general availability model could support.
Where it fell short
Mythos 5.1 uses different safeguards and restricted access; do not treat them as interchangeable products.
Release facts were checked against the sources below. Performance claims belong to the developers; we have not independently tested these models.
Developer announcement or release logBenchmark results
A benchmark estimate, not a percentage or capability multiplier. Reasoning settings are not specified in this source table. Historical estimates can change in later snapshots.
Epoch AI methodology ↗Download the source snapshotChecked Oct 7, 2026 · CC BY 4.0Selected highest effort variant where available in the current table. Starred partial results are excluded. Claude fallback configurations can use other models when safeguards intervene.
Source: Artificial Analysis Intelligence Index ↗Download selected resultsChecked Oct 8, 2026One explicitly named variant per release. Scores come from the same Overall snapshot; preliminary entries and reported intervals are preserved. These are current ratings of earlier variants, not their launch day ratings.
Source: Text Arena ↗Download selected resultsChecked Oct 8, 2026