Prices → Compare → GPT-5.3 Codex vs Gemini 3.1 Pro
GPT-5.3 Codex vs Gemini 3.1 Pro: API cost compared
GPT-5.3 Codex lists at $1.750 in / $14.00 out per 1M tokens. Gemini 3.1 Pro lists at $2.000 in / $12.00. Sticker price only tells you so much — below is what each actually costs across eight production workloads.
Side by side
| GPT-5.3 Codex | Gemini 3.1 Pro | |
|---|---|---|
| Provider | OpenAI | |
| Input per 1M | $1.750 | $2.000 |
| Output per 1M | $14.00 | $12.00 |
| Cached input per 1M | $0.175 | not published |
| Context window | 400k | 1M |
| Blended per 1M (3:1) | $4.812 | $4.500 |
Monthly cost by workload
Caching applied at each workload's typical hit rate. This is where the two models actually separate.
| Workload | GPT-5.3 Codex | Gemini 3.1 Pro | Cheaper | Difference |
|---|---|---|---|---|
| Customer support chatbot | $317.45 | $390.00 | GPT-5.3 Codex | $72.55 (19%) |
| RAG document Q&A | $385.00 | $464.00 | GPT-5.3 Codex | $79.00 (17%) |
| Coding agent | $224.88 | $344.00 | GPT-5.3 Codex | $119.12 (35%) |
| Bulk summarization | $2,566 | $2,880 | GPT-5.3 Codex | $314.50 (11%) |
| Structured data extraction | $3,710 | $5,000 | GPT-5.3 Codex | $1,290 (26%) |
| Long-form content generation | $585.55 | $520.00 | Gemini 3.1 Pro | $65.55 (11%) |
| Email triage agent | $861.87 | $1,360 | GPT-5.3 Codex | $498.13 (37%) |
| Translation pipeline | $3,718 | $3,330 | Gemini 3.1 Pro | $388.31 (10%) |
How to read this
GPT-5.3 Codex is cheaper on the majority of these workloads, but "majority" is not the decision. The output:input price ratio is 8.0 for GPT-5.3 Codex and 6.0 for Gemini 3.1 Pro. If your traffic is output-heavy — long-form drafting, translation — the model with the lower output price wins regardless of what the input price suggests. If you are input-heavy — RAG, bulk summarization, agents re-reading a codebase — the cached input rate matters more than either headline number.
Cost is also not the only axis. This site does not benchmark quality, latency, or rate limits, and a model that is 3x cheaper but needs two attempts per task is not cheaper. Use these numbers to size a bill, then validate on your own evals.
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| Model | In /1M | Out /1M | Monthly | vs best |
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