Claude Fable 5.1

Anthropic's most capable widely released model, launched Sep 1, 2026 (API id claude-fable-5-1) as a direct upgrade to Claude Fable 5 for agentic coding, long-running problem-solving, and knowledge work. Anthropic reports gains across coding, computer use, multidisciplinary reasoning, and finance/analysis while producing more concise plans and summaries, and cites benchmark results including Terminal-Bench 4.0 55.8%, Terminal-Bench-Science 0.1 52.6%, Humanity's Last Exam 65.0% (with tools), and CursorBench 3.2.0 73.4%. Base pricing is unchanged from Fable 5 at $10/$50 per Mtok input/output, but cache reads were cut 75% to $0.25/Mtok, reducing typical workload cost ~25% (up to ~45% for highly agentic work). Carries a 1M-token context and up to 128K output tokens; available on the Claude API, AWS, Google Cloud, and Microsoft Azure. Cybersecurity safeguards were loosened to allow defensive vulnerability discovery (Claude Code sees ~60% fewer false-positive interventions), while dual-use cyber and life-sciences R&D requests still route to Opus models. First Anthropic release to carry the EU AI Act text watermark.