Gemini 3.1 Pro Preview Custom Tools vs GPT-5.3-Codex
A side-by-side comparison of two multimodal models — real specs, pricing, strengths and weaknesses, and a clear verdict on which to choose. Kept current by our agents.
Quick verdict: which should you choose?
Choose Gemini 3.1 Pro Preview Custom Tools if you need
- ✓Choose Gemini 3.1 Pro Preview Custom Tools if you need very large context windows up to 1,048,756 tokens.
- ✓Choose Gemini 3.1 Pro Preview Custom Tools if you need lower output pricing at $12/1M.
- ✓Choose Gemini 3.1 Pro Preview Custom Tools if you need custom tools and strong cross-modal coherence on mixed inputs.
- ✓Choose Gemini 3.1 Pro Preview Custom Tools if you need flexible extension beyond narrow coding tasks.
Choose GPT-5.3-Codex if you need
- ✓Choose GPT-5.3-Codex if you need a measured intelligence index of 53.6.
- ✓Choose GPT-5.3-Codex if you need documented output speed of 101.39 t/s.
- ✓Choose GPT-5.3-Codex if you need specialization for programming workflows.
- ✓Choose GPT-5.3-Codex if you need extensive context handling within a 400,000-token limit.
Verdict
Gemini 3.1 Pro Preview Custom Tools leads on context scale and pricing with its 1,048,756-token window and $12/1M rate plus custom tools for flexible multimodal work, while GPT-5.3-Codex leads on measured performance with a 53.6 intelligence index and 101.39 t/s speed plus programming specialization. Gemini's preview status introduces potential instability risks absent from the GPT-5.3-Codex description. GPT-5.3-Codex's narrower coding focus contrasts with Gemini's broader cross-modal coherence claims.
Gemini 3.1 Pro Preview Custom Tools vs GPT-5.3-Codex: side by side
| Spec | Gemini 3.1 Pro Preview Custom Tools | GPT-5.3-Codex | Winner |
|---|---|---|---|
| Intelligence | — | 53.6 | Tie |
| Output speed | — | 101 t/s | Tie |
| Output price | $12.00/1M | $14.00/1M | Gemini 3.1 Pro Preview Custom Tools |
| Context | 1049K | 400K | Gemini 3.1 Pro Preview Custom Tools |
| Params | — | — | Tie |
| Type | Proprietary | Proprietary | Tie |
| Provider | OpenAI | Tie |
Detailed analysis
Context Window
Winner: Gemini 3.1 Pro Preview Custom ToolsGemini 3.1 Pro Preview Custom Tools provides a 1,048,756-token context window compared to GPT-5.3-Codex's 400,000 tokens. This gives Gemini a clear advantage for tasks requiring massive context handling. Both models list extensive context as a strength but Gemini's scale is substantially larger.
Pricing
Winner: Gemini 3.1 Pro Preview Custom ToolsGemini 3.1 Pro Preview Custom Tools is priced at $12 per million output tokens versus GPT-5.3-Codex at $14 per million. The lower rate favors Gemini for high-volume usage. No other cost factors are specified in the data.
Specialization
Winner: GPT-5.3-CodexGPT-5.3-Codex is described as specialized for programming workflows with support for diverse input types. Gemini 3.1 Pro Preview Custom Tools emphasizes general cross-modal coherence and custom tools instead. This makes GPT-5.3-Codex the clearer choice for coding-focused multimodal work.
Measured Performance
Winner: GPT-5.3-CodexGPT-5.3-Codex reports an intelligence index of 53.6 and output speed of 101.39 t/s. No equivalent metrics are provided for Gemini 3.1 Pro Preview Custom Tools. The available numbers therefore favor GPT-5.3-Codex where quantifiable performance matters.
Gemini 3.1 Pro Preview Custom Tools
Pros
- +Strong cross-modal coherence on mixed inputs
- +Effective use of very large context windows
- +Flexible extension via custom tools
Cons
- –Preview status may include occasional instability
- –Large contexts can increase latency and cost
- –Tool setup requires additional configuration
GPT-5.3-Codex
Pros
- +Specialized for programming workflows
- +Extensive context handling
- +Support for diverse input types
Cons
- –Narrower focus than general-purpose models
- –Performance tied to input quality
Summary: Gemini 3.1 Pro Preview Custom Tools vs GPT-5.3-Codex
Select Gemini 3.1 Pro Preview Custom Tools for maximum context, lower cost, and custom tool flexibility in multimodal scenarios. Select GPT-5.3-Codex when programming specialization and documented speed or intelligence metrics are priorities. The choice hinges on whether scale and price or measured coding performance drive the decision.
Frequently asked questions
Gemini 3.1 Pro Preview Custom Tools has the larger context window at 1,048,756 tokens versus GPT-5.3-Codex at 400,000 tokens.