Claude Opus 5

Claude Opus 5 is the flagship model of Anthropic's Claude 5 family, announced on 2026-07-24. It is a decoder-only transformer trained with large-scale pretraining, instruction tuning and preference optimisation (Constitutional AI / RLHF), and supports an adaptive "thinking" mode controllable through an `effort` parameter with five levels (low / medium / high / xhigh / max), defaulting to high.

Anthropic publishes a 194-page system card for Opus 5 alongside the launch announcement. It is a capability- and safety-evaluation document rather than a product spec sheet, so some API parameters (such as the 128k maximum output tokens) are documented only in Anthropic's separate models-overview table. The 1M-token context window, by contrast, is confirmed both in that table and directly in the system card (Sections 8.9 and 8.10.2).

At launch Opus 5 became the default model on Claude Max and the strongest model available on Claude Pro. Anthropic reclassified the prior flagship, Opus 4.8, as a "legacy" model and recommends migrating, though 4.8 is not deprecated and remains available. API pricing is unchanged from Opus 4.8 at $5 / $25 per million tokens, with an optional "fast mode" at roughly 2.5x speed for 2x the base price.

Modelglass records this entry's capability confidence as low. Anthropic's launch materials give mostly relative performance claims (for example "more than doubles Opus 4.8's performance on Frontier-Bench v0.1") rather than published numeric scores, and the independent SWE-bench Verified figure (97%, Vals AI leaderboard, #1) is the main externally verifiable capability number. A GDPval-AA score, assumed in the originating task brief, was not found anywhere in Anthropic's Opus 5 materials and is not cited here.