Claude Opus 5.5
by Anthropic · ID claude-opus-5-5 · Released 2026-09 · Proprietary
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ELO Score
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MMLU
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HumanEval
1M
Context Window
$4.00
Input Price
About Claude Opus 5.5
Anthropic's new default flagship, released 22 September 2026, priced 20% below Opus 5 at $4/$20 with cache reads down 60% to $0.20 per million. 1M-token context, 128K output as standard and 300K behind a beta header. Tops Terminal-Bench 4.0 at 66.4% and CursorBench 4.0 at 57.8%, trails GPT-6 Astra on AutomationBench and Terminal-Bench Science; Anthropic notes the margins sit close to the noise. The advertised 40% cost saving compares Opus 5.5 at its default medium effort against Opus 5 at high, and at the same effort it thinks more per turn. Ships four breaking API changes, including thinking that cannot be disabled and a new computer-use toolset. Not yet listed on the Arena text leaderboard as of 13 September 2026. Prices checked 23 September 2026.
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