DeepSeek V4 Flash vs GPT-5.3 Codex

Pick GPT-5.3 Codex if you want the stronger benchmark profile. DeepSeek V4 Flash only becomes the better choice if you want the cheaper token bill or you need the larger 1M context window.

GPT-5.3 Codex is clearly ahead on the provisional aggregate, 88 to 59. 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 49.1. The single biggest benchmark swing on the page is Terminal-Bench 2.0, 49.1% to 77.3%.

GPT-5.3 Codex is also the more expensive model on tokens at $1.75 input / $14.00 output per 1M tokens, versus $0.14 input / $0.28 output per 1M tokens for DeepSeek V4 Flash. That is roughly 50.0x on output cost alone. GPT-5.3 Codex is the reasoning model in the pair, while DeepSeek V4 Flash 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. DeepSeek V4 Flash gives you the larger context window at 1M, compared with 400K for GPT-5.3 Codex.