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Anthropic shipped Claude Opus 5.5 on 22 September at $4 per million input tokens and $20 per million output, a 20% list price cut. It scores 66.4% on Terminal-Bench 4.0 and 1846 Elo on GDPval-AA v2.1. Four breaking API changes will fail your existing integration if you upgrade without reading them.
Sep 23, 2026
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7 min read