Gemini 3.5 Flash vs GPT-5.1-Codex
How do these models stack up? Below is an expert side-by-side comparison of specifications, context window capacity, live pricing per million tokens, and standardized benchmark scores for Gemini 3.5 Flash and GPT-5.1-Codex.
Gemini 3.5 Flash
Gemini 3.5 Flash is Google's high-efficiency multimodal model, bringing near-Pro level coding and reasoning at Flash-tier cost and speed. It is highly optimized for coding proficiency and parallel agentic execution...
GPT-5.1-Codex
GPT-5.1-Codex is a specialized version of GPT-5.1 optimized for software engineering and coding workflows. It is designed for both interactive development sessions and long, independent execution of complex engineering tasks....
Technical Specifications
| Specification | Gemini 3.5 Flash | GPT-5.1-Codex |
|---|---|---|
| Provider | OpenAI | |
| Context Window | 1,048,576 tokens | 400,000 tokens |
| Agent Suitability | 88/100 | N/A |
| Time to First Token (TTFT) | 200 ms | N/A |
| Deployment Model | managed api | managed api |
| Production Stability | stable | stable |
| API Available | Yes | Yes |
| Released Date | 2026-05-19 | 2025-11-13 |
API Pricing Comparison
Input Price per Million Tokens
Gemini 3.5 Flash
$1.50
GPT-5.1-Codex
$1.25
Output Price per Million Tokens
Gemini 3.5 Flash
$9.00
GPT-5.1-Codex
$10.00
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Benchmark Performance Metrics
Scores show the raw performance percentages verified across key evaluation suites. Higher bars indicate superior accuracy and capability in that domain.
Gemini 3.5 Flash Quirks & Gotchas
- ▸Excellent multimodal performance — native video understanding
- ▸Tool calling via Google's native function_declarations in Vertex AI
GPT-5.1-Codex Quirks & Gotchas
No developer gotchas reported.