Name: Claude Fable 5.1
Author: Anthropic

Claude Fable 5.1

Anthropic · 2026-09-01

Claude Fable 5.1 is Anthropic's September 2026 model for coding, knowledge work, and long-running research. It shares the underlying model with Claude Mythos 5.1 and adds production safeguards; flagged cybersecurity and biology requests can fall back to Opus models.

Benchmark scores

Benchmark	Score
AA-AnalystAgent (pass@1)	65.8
AA-AnalystAgent (pass@5)	72.5
AA-AnalystAgent (pass^5)	57.5
AA-Briefcase Elo	1662
AA-Briefcase v1.1 Elo	1678
AA-LCR v1.1	85.3
AA-Omniscience Index	43.5
Agent Red Teaming k=100 (CAIS)	34.2
ALE-Bench	2849
Antidote: Everyday Edition	1065
ARC-AGI-1	97.5
ARC-AGI-2	90.0
Arena Code WebDev — Brand & Marketing	1737
Arena Code WebDev — Consumer Product	1669
Arena Code WebDev — Content Creation Tools	1734
Arena Code WebDev — Data & Analytics	1612
Arena Code WebDev — Gaming	1877
Arena Code WebDev — HTML	1676
Arena Code WebDev — React	1801
Arena Code WebDev — Reference-Based Design	1815
Arena Code WebDev — Simulations	1867
Arena Document (Style Controlled)	1493
Arena Image-to-WebDev	1710
Arena Text — Business, Management & Financial Ops (No Style Control)	1494
Arena Text — Chinese (No Style Control)	1605
Arena Text — Creative Writing (No Style Control)	1508
Arena Text — English (No Style Control)	1506
Arena Text — Entertainment, Sports & Media (No Style Control)	1495
Arena Text — Exclude Ties (No Style Control)	1527
Arena Text — Exclude Ties (Style Controlled)	1516