Claude Fable 5.1

Claude Fable 5.1 was released on 1 September 2026 with base pricing held at $10 per million input tokens and $50 output, while cache reads fell 75% from $1.00 to $0.25 per million; batch runs at $5/$25 and cache writes at $12.50 (5-minute) or $20 (1-hour). It carries a 1M-token context window and 128K maximum output. Reported results: 52.6% on Terminal-Bench-Science 0.1 against 24.7% for the prior Fable 5, 55.8% on Terminal-Bench 4.0, 73.4% on CursorBench 3.2.0 and 31.4% on AutomationBench. A companion release, Claude Mythos 5.1, is the same underlying model offered through a restricted-access programme for vetted cybersecurity and life-sciences organisations (described by MarkTechPost as vetted US organisations inside Project Glasswing) rather than as a separately purchasable product, so it is recorded here as a note rather than a second listing.