Gemini 3.1 Pro Preview Custom Tools vs Phi-3 Small 128K
Gemini 3.1 Pro Preview Custom Tools (2026) and Phi-3 Small 128K (2024) are compact production models from Google DeepMind and Microsoft Research. Gemini 3.1 Pro Preview Custom Tools ships a 1m-token context window, while Phi-3 Small 128K ships a 128k-token context window. On pricing, Phi-3 Small 128K costs $0.35/1M input tokens versus $2/1M for the alternative. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Phi-3 Small 128K is ~471% cheaper at $0.35/1M; pay for Gemini 3.1 Pro Preview Custom Tools only for long-context analysis.
Decision scorecard
Local evidence first| Signal | Gemini 3.1 Pro Preview Custom Tools | Phi-3 Small 128K |
|---|---|---|
| Best for | multimodal apps and long-context analysis | provider-routed production |
| Decision fit | RAG, Long context, and Vision | Coding, Long context, and Classification |
| Context window | 1m | 128k |
| Cheapest output | $12/1M tokens | $1.05/1M 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 uniquely exposes Vision, Multimodal, and Structured outputs in local model data.
- Local decision data tags Gemini 3.1 Pro Preview Custom Tools for RAG, Long context, and Vision.
- Phi-3 Small 128K has the lower cheapest tracked output price at $1.05/1M tokens.
- Phi-3 Small 128K has broader tracked provider coverage for fallback and procurement flexibility.
- Local decision data tags Phi-3 Small 128K for Coding, Long context, and Classification.
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
Phi-3 Small 128K
$543
Cheapest tracked route/tier: Microsoft Foundry
Estimated monthly gap: $4,058. 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 Phi-3 Small 128K; plan for SDK, billing, or endpoint changes.
- Phi-3 Small 128K is $10.95/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Vision, Multimodal, and Structured outputs before moving production traffic.
- No overlapping tracked provider route is sourced for Phi-3 Small 128K and Gemini 3.1 Pro Preview Custom Tools; plan for SDK, billing, or endpoint changes.
- Gemini 3.1 Pro Preview Custom Tools is $10.95/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Gemini 3.1 Pro Preview Custom Tools adds Vision, Multimodal, and Structured outputs in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-01-01 | 2024-05-21 |
| Context window | 1m | 128k |
| Parameters | — | 7B |
| Architecture | Decoder Only | Decoder Only |
| License | Proprietary | MITOSI-approved |
| Openness | Proprietary | Open source |
| Commercial use | Commercial use: conditional | Commercial use: permitted |
| Knowledge cutoff | 2025-01 | 2023-10 |
Pricing and availability
| Pricing attribute | Gemini 3.1 Pro Preview Custom Tools | Phi-3 Small 128K |
|---|---|---|
| Input price | $2/1M tokens | $0.35/1M tokens |
| Output price | $12/1M tokens | $1.05/1M tokens |
| Providers |
Capabilities
| Capability | Gemini 3.1 Pro Preview Custom Tools | Phi-3 Small 128K |
|---|---|---|
| Vision | Yes | No |
| Multimodal | Yes | No |
| Reasoning | No | No |
| Function calling | No | No |
| Tool use | No | No |
| Structured outputs | Yes | No |
| Code execution | No | No |
| 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 vision: Gemini 3.1 Pro Preview Custom Tools, multimodal input: Gemini 3.1 Pro Preview Custom Tools, and structured outputs: Gemini 3.1 Pro Preview Custom Tools. Both models share the core language-model surface, 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 Phi-3 Small 128K lists $0.35/1M input and $1.05/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Phi-3 Small 128K lower by about $4.44 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 Phi-3 Small 128K when provider fit, 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 Phi-3 Small 128K?
Gemini 3.1 Pro Preview Custom Tools supports 1m tokens, while Phi-3 Small 128K supports 128k 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 Phi-3 Small 128K?
Phi-3 Small 128K is cheaper on tracked token pricing. Gemini 3.1 Pro Preview Custom Tools costs $2/1M input and $12/1M output tokens. Phi-3 Small 128K costs $0.35/1M input and $1.05/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Gemini 3.1 Pro Preview Custom Tools or Phi-3 Small 128K open source?
Gemini 3.1 Pro Preview Custom Tools is listed under Proprietary. Phi-3 Small 128K is listed under MIT. 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 Phi-3 Small 128K?
Gemini 3.1 Pro Preview Custom Tools has the clearer documented vision signal in this comparison. If vision is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Which is better for multimodal input, Gemini 3.1 Pro Preview Custom Tools or Phi-3 Small 128K?
Gemini 3.1 Pro Preview Custom Tools has the clearer documented multimodal input signal in this comparison. If multimodal input is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run Gemini 3.1 Pro Preview Custom Tools and Phi-3 Small 128K?
Gemini 3.1 Pro Preview Custom Tools is available on OpenRouter. Phi-3 Small 128K is available on Microsoft Foundry and NVIDIA NIM. 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.