Model detail
Gemini 3.1 Pro Preview Custom Tools
Gemini 3.1 Pro Preview Custom Tools is a variant of Gemini 3.1 Pro that improves tool selection behavior by preventing overuse of a general bash tool when more efficient third-party or user-defined functions are available. This specialized preview endpoint significantly increases function calling reliability and ensures the model selects the most appropriate tool in coding agents and complex, multi-tool workflows. It retains the core strengths of Gemini 3.1 Pro, including multimodal reasoning across text, image, video, audio, and code, a 1M-token context window, and strong software engineering performance.
Model specs
- Model ID
-
gemini-3.1-pro-preview-customtools
- Context length
- 1.048576M
- Max output
- 65.536K
- I/O modalities
- Released
- 2026-02
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API endpoints
One MixRoute gateway, OpenAI-compatible
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Gemini
/v1beta/models/{model}:generateContentPOST -
OpenAI-compatible
/v1/chat/completionsPOST
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Tiered pricing
Unit: /1M Tokens
| Tier | Input /1M Tokens | Output /1M Tokens | Cache read /1M Tokens |
|---|---|---|---|
| standard Length ≤ 200K | $2.0000 | $12.0000 | $0.2000 |
| long_context Length > 200K | $4.0000 | $18.0000 | $0.4000 |
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Selection summary
Quickly judge whether it fits your workload
What is this model good for?
Variant of Gemini 3.1 Pro that improves tool selection behavior by preventing overuse
Gemini 3.1 Pro Preview Custom Tools is a variant of Gemini 3.1 Pro that improves tool selection behavior by preventing overuse of a general bash tool when more efficient third-party or user-defined functions are available.
What should you check before using it?
1,048,576 context, 65,536 output tokens
Model type: text. Verify supported features and quotas with the provider documentation. Knowledge cutoff: 2025-01. Released 2026-02-19.
Why use it through MixRoute?
Gemini 3.1 Pro Preview Custom Tools cache reads cut repeated-prompt cost
Cached prefixes are billed at $0.2000 per 1M tokens for inputs up to 200,000 tokens (standard input $2.0000); above that, $0.4000 and $4.0000 respectively, so repeated system prompts cost less. MixRoute serves Gemini 3.1 Pro Preview Custom Tools on the OpenAI-compatible endpoint /v1/chat/completions; point your existing client at https://api.mixroute.ai/v1 with the model ID gemini-3.1-pro-preview-customtools and re-run your integration tests.
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Capabilities & compatibility
Unconfirmed capabilities stay "Unknown," no guesses
Tool calling
Gemini 3.1 Pro Preview Custom Tools supports function and tool calls.
tools definition; the response returns tool_calls to execute and feed results back.
Structured output
Gemini 3.1 Pro Preview Custom Tools can produce JSON-formatted output on demand.
response_format: { type: "json_schema" } forces valid JSON output.
Streaming
Gemini 3.1 Pro Preview Custom Tools supports streamed responses.
stream: true streams tokens incrementally, so chat UIs render as they arrive.
Prompt caching
Gemini 3.1 Pro Preview Custom Tools supports prompt caching under supported routing conditions.
Vision input
Gemini 3.1 Pro Preview Custom Tools can process image inputs alongside text.
image_url content part alongside text messages.
OpenAI SDK
Call Gemini 3.1 Pro Preview Custom Tools through MixRoute's OpenAI-compatible endpoint.
base_url to https://api.mixroute.ai/v1; everything else follows the OpenAI style.
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Token cost estimator
Live estimate from this page's pricing, not an actual bill
Share of the same prefix read repeatedly, up to 100%
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FAQ
A cache hit on Gemini 3.1 Pro Preview Custom Tools requires an identical prompt prefix across requests. Put your stable instructions and reference material at the start of the prompt, keep them byte-identical, and let the changing part follow. Cached reads are then billed at the cache rate rather than the input rate.
One endpoint, a testable decision
Test this model and alternate routes with the same request format
Start from a real workload, then let quality, total cost, and failure conditions decide whether to send production traffic.