Gemini 3.5 Flash vs GPT-5.3 Codex
Detailed comparison of API pricing, technical specifications, and benchmark scores. Updated 2026-06-29.
Cost at a Glance
GPT-5.3 Codex is 10× more expensive than Gemini 3.5 Flash — switching could save 90% on your monthly API bill.
At 5M input + 2M output tokens per month:
Choosing Gemini 3.5 Flash could save you $38.25/mo
Price Comparison (per 1M tokens)
| Metric | Gemini 3.5 Flash | GPT-5.3 Codex |
|---|---|---|
| Input (per 1M tokens) | $0.25 | $2.50 |
| Output (per 1M tokens) | $1.50 | $15.00 |
| Cache Write (per 1M tokens) | — | $3.13 |
| Cache Read (per 1M tokens) | $0.03 | $0.25 |
| Batch Input (per 1M tokens) | — | $1.25 |
| Batch Output (per 1M tokens) | — | $7.50 |
Prices are per 1 million tokens. Actual costs depend on your monthly token volume. Use the calculator →
Specifications
| Spec | Gemini 3.5 Flash | GPT-5.3 Codex |
|---|---|---|
| Context Window | 1M | 1M |
| Max Output Tokens | 64K | 128K |
| Knowledge Cutoff | 2026-04 | 2025-10 |
| Modalities | Text, Image | Text |
| Prompt Caching | Yes | Yes |
| Batch API | No | Yes |
| Thinking / Reasoning | No | No |
Benchmark Scores
| Benchmark | Gemini 3.5 Flash | GPT-5.3 Codex |
|---|---|---|
| SWE-bench Verified | 65.0 | 82.0 |
| MMLU-Pro | 80.0 | 83.0 |
| HumanEval | 90.0 | 94.5 |
Benchmark scores from official provider reports. Higher is better. Missing scores indicate the provider has not published that benchmark yet.
Use Cases
Gemini 3.5 Flash
GPT-5.3 Codex
About the Providers
Gemini 3.5 Flash is developed by Google. GPT-5.3 Codex is developed by OpenAI. This is a cross-provider comparison between Google and OpenAI models. For the most up-to-date pricing, always check the official API documentation from each provider.