Gemini 3.1 Pro Preview Custom Tools vs GPT-5.1-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
- ✓massive 1,048,756-token context windows for mixed inputs
- ✓custom tools and strong cross-modal coherence
- ✓very large context handling without reported coherence loss
- ✓flexible extension beyond standard text-image tasks
Choose GPT-5.1-Codex if you need
- ✓extended coding workflows with visual context integration
- ✓lower $10 per million output price and measured 178.06 t/s speed
- ✓specialized software development performance on large inputs
- ✓known intelligence index of 43.1 with no preview instability noted
Verdict
Gemini 3.1 Pro Preview Custom Tools leads on context scale and custom tool flexibility while GPT-5.1-Codex leads on known speed, lower price, and coding specialization. Gemini's 1,048,756-token window dwarfs GPT-5.1-Codex's 400,000 tokens, but GPT-5.1-Codex is cheaper at $10 per million versus $12 and reports 178.06 t/s output speed where Gemini's speed remains unreported. Both are proprietary multimodal models, yet Gemini's preview status introduces potential instability absent from the GPT-5.1-Codex description.
Gemini 3.1 Pro Preview Custom Tools vs GPT-5.1-Codex: side by side
| Spec | Gemini 3.1 Pro Preview Custom Tools | GPT-5.1-Codex | Winner |
|---|---|---|---|
| Intelligence | — | 43.1 | Tie |
| Output speed | — | 178 t/s | Tie |
| Output price | $12.00/1M | $10.00/1M | GPT-5.1-Codex |
| 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 1,048,756 tokens compared with GPT-5.1-Codex's 400,000 tokens. This gives Gemini a clear advantage for very large mixed inputs. GPT-5.1-Codex still handles large inputs without losing coherence but at a smaller scale.
Pricing
Winner: GPT-5.1-CodexGPT-5.1-Codex costs $10 per million output tokens while Gemini 3.1 Pro Preview Custom Tools costs $12 per million. The $2 difference favors GPT-5.1-Codex on cost-sensitive workloads. Both prices apply to proprietary models from their respective providers.
Specialization and Tools
Winner: Gemini 3.1 Pro Preview Custom ToolsGemini 3.1 Pro Preview Custom Tools emphasizes custom tools and cross-modal coherence on mixed inputs. GPT-5.1-Codex focuses on coding workflows and visual-code integration. Each model aligns with different primary use cases.
Speed and Intelligence Data
Winner: GPT-5.1-CodexGPT-5.1-Codex reports an output speed of 178.06 t/s and intelligence index of 43.1. Gemini 3.1 Pro Preview Custom Tools leaves both metrics unreported. Direct numerical comparison is therefore possible only for GPT-5.1-Codex.
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-5.1-Codex
Pros
- +Strong performance on extended coding workflows
- +Effective integration of visual context with code
- +Handles very large inputs without losing coherence
- +Specialized for software development tasks
Cons
- –Limited to text and image inputs only
- –High computational cost for maximum context
- –May require careful prompt engineering for complex tasks
Summary: Gemini 3.1 Pro Preview Custom Tools vs GPT-5.1-Codex
Choose Gemini 3.1 Pro Preview Custom Tools when maximum context and custom tooling matter most. Choose GPT-5.1-Codex when coding specialization, lower price, and known performance metrics are priorities. The models serve overlapping multimodal needs but diverge on scale versus specialization.
Frequently asked questions
Gemini 3.1 Pro Preview Custom Tools has the larger context window at 1,048,756 tokens versus GPT-5.1-Codex's 400,000 tokens.