GPT-5.3 Codex vs Kimi K2.5

Pick GPT-5.3 Codex if you want the stronger benchmark profile. Kimi K2.5 only becomes the better choice if coding is the priority or you want the cheaper token bill.

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 54.6. The single biggest benchmark swing on the page is Terminal-Bench 2.0, 77.3% to 50.8%. Kimi K2.5 does hit back in coding, so the answer changes if that is the part of the workload you care about most.

GPT-5.3 Codex is also the more expensive model on tokens at $2.50 input / $10.00 output per 1M tokens, versus $0.50 input / $2.80 output per 1M tokens for Kimi K2.5. That is roughly 3.6x on output cost alone. GPT-5.3 Codex is the reasoning model in the pair, while Kimi K2.5 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 256K for Kimi K2.5.