Claude Sonnet 4.5 vs GPT-5.3 Codex

Pick GPT-5.3 Codex if you want the stronger benchmark profile. Claude Sonnet 4.5 only becomes the better choice if coding is the priority or you would rather avoid the extra latency and token burn of a reasoning model.

GPT-5.3 Codex is clearly ahead on the provisional aggregate, 89 to 68. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.

GPT-5.3 Codex's sharpest advantage is in agentic, where it averages 71.5 against 55.3. The single biggest benchmark swing on the page is Terminal-Bench 2.0, 50% to 77.3%. Claude Sonnet 4.5 does hit back in coding, so the answer changes if that is the part of the workload you care about most.

Claude Sonnet 4.5 is also the more expensive model on tokens at $3.00 input / $15.00 output per 1M tokens, versus $2.50 input / $10.00 output per 1M tokens for GPT-5.3 Codex. GPT-5.3 Codex is the reasoning model in the pair, while Claude Sonnet 4.5 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. GPT-5.3 Codex gives you the larger context window at 400K, compared with 200K for Claude Sonnet 4.5.