Claude Opus 4.6 vs GPT-5.3 Codex

Pick Claude Opus 4.6 if you want the stronger benchmark profile. GPT-5.3 Codex only becomes the better choice if you want the cheaper token bill or you want the stronger reasoning-first profile.

Claude Opus 4.6 finishes one point ahead on BenchLM's provisional leaderboard, 87 to 86. That is enough to call, but not enough to treat as a blowout. This matchup comes down to a few meaningful edges rather than one model dominating the board.

Claude Opus 4.6's sharpest advantage is in coding, where it averages 64.4 against 63.1. The single biggest benchmark swing on the page is Terminal-Bench 2.0, 65.4% to 77.3%.

Claude Opus 4.6 is also the more expensive model on tokens at $5.00 input / $25.00 output per 1M tokens, versus $1.75 input / $14.00 output per 1M tokens for GPT-5.3 Codex. GPT-5.3 Codex is the reasoning model in the pair, while Claude Opus 4.6 is not. That usually helps on harder chain-of-thought-heavy tests, but it can also mean more latency and more token spend in real use. Claude Opus 4.6 gives you the larger context window at 1M, compared with 400K for GPT-5.3 Codex.