Anthropic's Mythos-class flagship (June 2026) — the new benchmark leader for agentic coding, at a premium price.
Claude Fable 5 is the first Mythos-class model Anthropic has made generally available (June 9, 2026), positioned above Opus in capability. On Anthropic's published numbers it leads nearly every benchmark — 80.3% on SWE-Bench Pro versus GPT-5.5's 58.6%, and +11 points over Opus 4.8 — with a 1M-token context and 128K output. It is priced accordingly at roughly twice Opus ($10/$50 per million tokens), which makes it a deliberate escalation target rather than a daily default for most agent workloads.
The hardest autonomous coding and reasoning work, where the quality ceiling pays for itself.
The model picks the moves; the agent runs the loop, the tools, and the guardrails. Once you've chosen a model, see which agent gets the most out of it.