Gemini 3.1 Pro Preview Custom Tools vs GPT-5.2 Codex
Gemini 3.1 Pro Preview Custom Tools (2026) and GPT-5.2 Codex (2025) compare a standalone API model against a coding-specialized model. Gemini 3.1 Pro Preview Custom Tools ships a 1m-token context window, while GPT-5.2 Codex ships a 400k-token context window. On pricing, GPT-5.2 Codex costs $1.75/1M input tokens versus $2/1M for the alternative. This page treats the result as workflow and deployment fit, not a universal model winner.
Treat this as a product-type comparison: Gemini 3.1 Pro Preview Custom Tools is standalone API model, while GPT-5.2 Codex is coding-specialized model. Choose based on workflow fit before reading any benchmark or price row as decisive.
Decision scorecard
Local evidence first| Signal | Gemini 3.1 Pro Preview Custom Tools | GPT-5.2 Codex |
|---|---|---|
| Product type | Standalone API model | Coding-specialized model |
| Best for | multimodal apps and long-context analysis | custom coding agents, code generation, and tool loops |
| Decision fit | RAG, Long context, and Vision | Coding, RAG, and Agents |
| Context window | 1m | 400k |
| Cheapest output | $12/1M tokens | $14/1M tokens |
| Provider routes | 1 tracked | 2 tracked |
| Shared benchmarks | 0 shared | 0 shared |
Decision tradeoffs
- Gemini 3.1 Pro Preview Custom Tools has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Gemini 3.1 Pro Preview Custom Tools has the lower cheapest tracked output price at $12/1M tokens.
- Local decision data tags Gemini 3.1 Pro Preview Custom Tools for RAG, Long context, and Vision.
- GPT-5.2 Codex has broader tracked provider coverage for fallback and procurement flexibility.
- GPT-5.2 Codex uniquely exposes Reasoning, Function calling, and Tool use in local model data.
- Local decision data tags GPT-5.2 Codex for Coding, RAG, and Agents.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Gemini 3.1 Pro Preview Custom Tools
$4,600
Cheapest tracked route/tier: OpenRouter
GPT-5.2 Codex
$4,900
Cheapest tracked route/tier: Vercel AI Gateway
Estimated monthly gap: $300. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for Gemini 3.1 Pro Preview Custom Tools and GPT-5.2 Codex; plan for SDK, billing, or endpoint changes.
- GPT-5.2 Codex is $2/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- GPT-5.2 Codex adds Reasoning, Function calling, and Tool use in local capability data.
- No overlapping tracked provider route is sourced for GPT-5.2 Codex and Gemini 3.1 Pro Preview Custom Tools; plan for SDK, billing, or endpoint changes.
- Gemini 3.1 Pro Preview Custom Tools is $2/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Reasoning, Function calling, and Tool use before moving production traffic.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-01-01 | 2025-12-18 |
| Context window | 1m | 400k |
| Parameters | — | — |
| Architecture | Decoder Only | Decoder Only |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Weights | Not released | Not released |
| Code | Unknown | Unknown |
| Commercial use | Commercial use: conditional | Commercial use: conditional |
| Knowledge cutoff | 2025-01 | 2025-08 |
Pricing and availability
| Pricing attribute | Gemini 3.1 Pro Preview Custom Tools | GPT-5.2 Codex |
|---|---|---|
| Input price | $2/1M tokens | $1.75/1M tokens |
| Output price | $12/1M tokens | $14/1M tokens |
| Providers |
Capabilities
| Capability | Gemini 3.1 Pro Preview Custom Tools | GPT-5.2 Codex |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | No | Yes |
| Function calling | No | Yes |
| Tool use | No | Yes |
| Structured outputs | Yes | Yes |
| Code execution | No | Yes |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
No shared benchmark scores are currently available for this pair.
Deep dive
The capability footprint differs most on reasoning mode: GPT-5.2 Codex, function calling: GPT-5.2 Codex, tool use: GPT-5.2 Codex, and code execution: GPT-5.2 Codex. Both models share vision, multimodal input, and structured outputs, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
For cost, Gemini 3.1 Pro Preview Custom Tools lists $2/1M input and $12/1M output tokens on the cheapest tracked provider, while GPT-5.2 Codex lists $1.75/1M input and $14/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Gemini 3.1 Pro Preview Custom Tools lower by about $0.42 per million blended tokens. Availability is 1 providers versus 2, so concentration risk also matters.
Choose Gemini 3.1 Pro Preview Custom Tools when long-context analysis and larger context windows are central to the workload. Choose GPT-5.2 Codex when coding workflow support, lower input-token cost, and broader provider choice are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship.
FAQ
Which has a larger context window, Gemini 3.1 Pro Preview Custom Tools or GPT-5.2 Codex?
Gemini 3.1 Pro Preview Custom Tools supports 1m tokens, while GPT-5.2 Codex supports 400k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, Gemini 3.1 Pro Preview Custom Tools or GPT-5.2 Codex?
Gemini 3.1 Pro Preview Custom Tools is cheaper on tracked token pricing. Gemini 3.1 Pro Preview Custom Tools costs $2/1M input and $12/1M output tokens. GPT-5.2 Codex costs $1.75/1M input and $14/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Gemini 3.1 Pro Preview Custom Tools or GPT-5.2 Codex open source?
Gemini 3.1 Pro Preview Custom Tools is listed under Proprietary. GPT-5.2 Codex is listed under Proprietary. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for vision, Gemini 3.1 Pro Preview Custom Tools or GPT-5.2 Codex?
Both Gemini 3.1 Pro Preview Custom Tools and GPT-5.2 Codex expose vision. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Which is better for multimodal input, Gemini 3.1 Pro Preview Custom Tools or GPT-5.2 Codex?
Both Gemini 3.1 Pro Preview Custom Tools and GPT-5.2 Codex expose multimodal input. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface.
Where can I run Gemini 3.1 Pro Preview Custom Tools and GPT-5.2 Codex?
Gemini 3.1 Pro Preview Custom Tools is available on OpenRouter. GPT-5.2 Codex is available on Vercel AI Gateway and OpenAI API. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-06-30. Data sourced from public model cards and provider documentation.