Gemini 3.1 Pro Preview Custom Tools Endpoint
Google released a new Gemini 3.1 Pro preview endpoint optimized for custom tool prioritization, supporting text and image inputs with a large context window.
Official Release Details
The source event date is February 19, 2026. On this date, Google announced the release of a separate endpoint named gemini-3.1-pro-preview-customtools. The official changelog states that this endpoint is better at prioritizing custom tools for users building with a mix of bash and tools. This announcement distinguishes the specific release date from the current publication date of this article.
- Provider: Google
- Model Name: Gemini 3.1 Pro Preview Custom Tools
- Endpoint ID: gemini-3.1-pro-preview-customtools
- Event Type: Preview
Technical Specifications
The model accepts text and image as input modalities and produces text as its output modality. The documented context window is 1,048,576 tokens, while the maximum output length is set to 65,536 tokens. The source indicates that open weights are not confirmed for this model. No pricing information is provided in the verified facts. The description notes that the model is optimized for custom tool usage within the Gemini family.
- Input Modalities: Text, Image
- Output Modality: Text
- Context Window: 1,048,576 tokens
- Max Output Tokens: 65,536
- Open Weights: Not Confirmed
Evaluation Procedure
Engineers can evaluate this model by designing tests that compare tool selection behavior against standard endpoints. A practical procedure involves creating a test suite where the model must choose between a custom tool and a bash command for identical tasks. Measure the frequency with which the custom tool is selected over bash. Compare these results with the baseline Gemini 3.1 Pro Preview endpoint to validate if the prioritization improvement holds under consistent conditions. Do not assume performance gains without direct measurement. The source confirms the intent to prioritize custom tools but does not provide benchmark data or guaranteed operational benefits.
- Test: Create scenarios mixing bash and custom tools.
- Measure: Record selection frequency for custom tools vs. bash.
- Compare: Contrast results with the non-custom-tools preview endpoint.
- Validate: Confirm if prioritization aligns with developer expectations.
Primary sources
Frequently asked questions
What is the primary difference between this endpoint and the standard Gemini 3.1 Pro Preview?
The source states that the gemini-3.1-pro-preview-customtools endpoint is better at prioritizing custom tools for users building with a mix of bash and tools. It is a separate endpoint launched specifically for this optimization.
Can I install this model locally using open weights?
The source records that open weights are not confirmed. It does not establish whether local installation is possible or impossible, nor does it specify hosting arrangements. Engineers should verify availability through official channels before planning deployment.