Gemini 3.1 Pro Preview Custom Tools

Gemini 3.1 Pro Preview Custom Tools is presented by third-party routing interfaces as a Google-built variant within the Gemini 3 reasoning family, built on the multimodal foundation that already handles text, image, video, audio, and code. The "Custom Tools" designation is described as a routing configuration of Gemini 3.1 Pro Preview rather than a separately trained model, pointing the same underlying reasoning engine at custom tool integrations. This makes the variant well suited to developers who want to plug a frontier reasoning model into their own tool orchestration layer without giving up native multimodal inputs.

Practically, the variant is positioned for advanced software engineering and agentic workflows where long-horizon stability and reliable tool use matter. Gateway descriptions highlight enhanced software-engineering performance, improved agentic reliability, and more efficient token usage compared with earlier Gemini reasoning checkpoints, along with stronger autonomous task execution in structured domains such as finance and spreadsheet-driven work. A new medium thinking level is reported to help balance cost, speed, and depth on multi-step tasks, and the very large input window supports extensive codebases, long documents, and sustained multi-turn tool-calling sessions that demand preserved reasoning across turns.