Gemini 3.1 Pro Preview Custom Tools vs o3
Gemini 3.1 Pro Preview Custom Tools (2026) and o3 (2025) are frontier reasoning models from Google DeepMind and OpenAI. Gemini 3.1 Pro Preview Custom Tools ships a 1m-token context window, while o3 ships a 200k-token context window. On pricing, both list $2/1M input tokens on the cheapest tracked route. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Gemini 3.1 Pro Preview Custom Tools fits 5x more tokens; pick it for long-context work and o3 for tighter calls.
Decision scorecard
Local evidence first| Signal | Gemini 3.1 Pro Preview Custom Tools | o3 |
|---|---|---|
| Best for | multimodal apps and long-context analysis | reasoning-heavy apps, multimodal apps, and tool-calling agents |
| Decision fit | RAG, Long context, and Vision | Coding, RAG, and Agents |
| Context window | 1m | 200k |
| Cheapest output | $12/1M tokens | $8/1M tokens |
| Provider routes | 1 tracked | 3 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.
- Local decision data tags Gemini 3.1 Pro Preview Custom Tools for RAG, Long context, and Vision.
- o3 has the lower cheapest tracked output price at $8/1M tokens.
- o3 has broader tracked provider coverage for fallback and procurement flexibility.
- o3 uniquely exposes Reasoning, Function calling, and Tool use in local model data.
- Local decision data tags o3 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
o3
$3,600
Cheapest tracked route/tier: OpenAI API
Estimated monthly gap: $1,000. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- o3 is $4/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- o3 adds Reasoning, Function calling, and Tool use in local capability data.
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- Gemini 3.1 Pro Preview Custom Tools is $4/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Reasoning, Function calling, and Tool use before moving production traffic.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-01-01 | 2025-04-16 |
| Context window | 1m | 200k |
| Parameters | — | — |
| Architecture | Decoder Only | Decoder Only |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Commercial use | Commercial use: conditional | Commercial use: conditional |
| Knowledge cutoff | 2025-01 | 2024-06 |
Pricing and availability
| Pricing attribute | Gemini 3.1 Pro Preview Custom Tools | o3 |
|---|---|---|
| Input price | $2/1M tokens | $2/1M tokens |
| Output price | $12/1M tokens | $8/1M tokens |
| Providers |
Capabilities
| Capability | Gemini 3.1 Pro Preview Custom Tools | o3 |
|---|---|---|
| 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: o3, function calling: o3, tool use: o3, and code execution: o3. 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 o3 lists $2/1M input and $8/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts o3 lower by about $1.20 per million blended tokens. Availability is 1 providers versus 3, 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 o3 when coding workflow support 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. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions.
FAQ
Which has a larger context window, Gemini 3.1 Pro Preview Custom Tools or o3?
Gemini 3.1 Pro Preview Custom Tools supports 1m tokens, while o3 supports 200k 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 o3?
o3 is cheaper on tracked token pricing. Gemini 3.1 Pro Preview Custom Tools costs $2/1M input and $12/1M output tokens. o3 costs $2/1M input and $8/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Gemini 3.1 Pro Preview Custom Tools or o3 open source?
Gemini 3.1 Pro Preview Custom Tools is listed under Proprietary. o3 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 o3?
Both Gemini 3.1 Pro Preview Custom Tools and o3 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 o3?
Both Gemini 3.1 Pro Preview Custom Tools and o3 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 o3?
Gemini 3.1 Pro Preview Custom Tools is available on OpenRouter. o3 is available on OpenAI API, OpenRouter, and Vercel AI Gateway. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
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Last reviewed: 2026-06-15. Data sourced from public model cards and provider documentation.