Gemini 3.1 Pro Preview vs GPT-5.2 Codex
Gemini 3.1 Pro Preview (2026) and GPT-5.2 Codex (2025) compare a standalone API model against a coding-specialized model. Gemini 3.1 Pro Preview ships a 1m-token context window, while GPT-5.2 Codex ships a 400k-token context window. On SWE-bench Verified, Gemini 3.1 Pro Preview leads by 7.8 pts. 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 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 | GPT-5.2 Codex |
|---|---|---|
| Product type | Standalone API model | Coding-specialized model |
| Best for | multimodal apps, tool-calling agents, and long-context analysis | custom coding agents, code generation, and tool loops |
| Decision fit | Coding, RAG, and Agents | Coding, RAG, and Agents |
| Context window | 1m | 400k |
| Cheapest output | $12/1M tokens | $14/1M tokens |
| Provider routes | 5 tracked | 2 tracked |
| Shared benchmarks | SWE-bench Verified leader | 2 shared |
Decision tradeoffs
- Gemini 3.1 Pro Preview holds a shared-benchmark lead on SWE-bench Verified, ahead by 7.8 points.
- Gemini 3.1 Pro Preview has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Gemini 3.1 Pro Preview has the lower cheapest tracked output price at $12/1M tokens.
- Gemini 3.1 Pro Preview has broader tracked provider coverage for fallback and procurement flexibility.
- Local decision data tags Gemini 3.1 Pro Preview for Coding, RAG, and Agents.
- GPT-5.2 Codex holds a shared-benchmark lead on SWE-bench Pro, ahead by 2.2 points.
- GPT-5.2 Codex uniquely exposes Reasoning 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
$4,600
Cheapest tracked route/tier: Google AI Studio
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
- Provider overlap exists on Vercel AI Gateway; start route-level A/B tests there.
- 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 in local capability data.
- Provider overlap exists on Vercel AI Gateway; start route-level A/B tests there.
- Gemini 3.1 Pro Preview is $2/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Reasoning before moving production traffic.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-02-19 | 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 | GPT-5.2 Codex |
|---|---|---|
| Input price |
| $1.75/1M tokens |
| Output price |
| $14/1M tokens |
| Providers |
Capabilities
| Capability | Gemini 3.1 Pro Preview | GPT-5.2 Codex |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | No | Yes |
| Function calling | Yes | Yes |
| Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Code execution | Yes | Yes |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
| Benchmark | Gemini 3.1 Pro Preview | GPT-5.2 Codex |
|---|---|---|
| SWE-bench Verified | 80.6 | 72.8 |
| SWE-bench Pro | 54.2 | 56.4 |
Deep dive
On shared benchmark coverage, SWE-bench Verified has Gemini 3.1 Pro Preview at 80.6 and GPT-5.2 Codex at 72.8, with Gemini 3.1 Pro Preview ahead by 7.8 points; SWE-bench Pro has Gemini 3.1 Pro Preview at 54.2 and GPT-5.2 Codex at 56.4, with GPT-5.2 Codex ahead by 2.2 points. The largest visible gap is 7.8 points on SWE-bench Verified, which matters most when that benchmark mirrors your workload. Treat isolated benchmark wins as directional, because provider routing, prompt style, and tool access can move real application results.
The capability footprint differs most on reasoning mode: GPT-5.2 Codex. Both models share vision, multimodal input, function calling, and tool use, 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 lists tiered pricing: 0-200,001t is $2/1M input and $12/1M output; 200,001t+ is $4/1M input and $18/1M output, 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 lower by about $0.42 per million blended tokens. For tiered rows, this cheapest-track view can understate interactive or fast-lane spend, so compare the tier you will actually use. Availability is 5 providers versus 2, so concentration risk also matters.
Choose Gemini 3.1 Pro Preview when coding workflow support, larger context windows, and broader provider choice are central to the workload. Choose GPT-5.2 Codex when coding workflow support and lower input-token cost 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 or GPT-5.2 Codex?
Gemini 3.1 Pro Preview 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 or GPT-5.2 Codex?
Gemini 3.1 Pro Preview lists tiered pricing: 0-200,001t is $2/1M input and $12/1M output; 200,001t+ is $4/1M input and $18/1M output. GPT-5.2 Codex lists $1.75/1M input and $14/1M output tokens on the cheapest tracked provider. Compare the tier you will actually use; cheap async pricing can overstate savings for interactive workflows. Provider discounts or batch pricing can still change the final bill.
Is Gemini 3.1 Pro Preview or GPT-5.2 Codex open source?
Gemini 3.1 Pro Preview 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 or GPT-5.2 Codex?
Both Gemini 3.1 Pro Preview 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 or GPT-5.2 Codex?
Both Gemini 3.1 Pro Preview 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 and GPT-5.2 Codex?
Gemini 3.1 Pro Preview is available on Google AI Studio, GCP Vertex AI, OpenRouter, Replicate API, and Vercel AI Gateway. 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.