Gemini 3.1 Pro Custom Tools (Preview) API — pricing & specs

Gemini 3.1 Pro Custom Tools (Preview), made by Google DeepMind, accepts text, image, audio, video, and pdf input and returns text. On KeepRouter, Gemini 3.1 Pro Custom Tools (Preview) costs $4.00 per 1M input tokens and $18.00 per 1M output tokens, billed pay-as-you-go with no monthly fee. Call it through a compatible KeepRouter endpoint supported by its active route, with the model id gemini-3.1-pro-preview-customtools.

MakerGoogle DeepMind
ModalityText, vision, audio, video, PDF
Context window1,048,576 tokens
Max output65,536 tokens
Input price$4.00 per 1M tokens
Output price$18.00 per 1M tokens
Cached input$0.4000 per 1M tokens
CapabilitiesAudio input, Video input, Vision (image input), Chat completions, Streaming where supported, Tool calling where supported
EndpointPOST /v1/chat/completions or POST /v1/messages (compatible chat routes)
Model idgemini-3.1-pro-preview-customtools

How pricing works for Gemini 3.1 Pro Custom Tools (Preview)

Gemini 3.1 Pro Custom Tools (Preview) is billed per token — $4.00 per 1M input tokens and $18.00 per 1M output tokens, with cached input at $0.4000 per 1M tokens. The published price is pay-as-you-go, with no monthly fee; actual request cost depends on measured token usage.

Calling Gemini 3.1 Pro Custom Tools (Preview) on KeepRouter

Point a compatible client at the supported KeepRouter endpoint and set the model to gemini-3.1-pro-preview-customtools. KeepRouter preserves the client-facing request shape while handling upstream routing or translation. Use POST /v1/chat/completions or, on compatible chat routes, POST /v1/messages; streaming and tool support depend on the model's active route.

cURL

curl https://keeprouter.com/v1/chat/completions \
  -H "Authorization: Bearer $KEEPROUTER_KEY" -H "Content-Type: application/json" \
  -d '{"model":"gemini-3.1-pro-preview-customtools","messages":[{"role":"user","content":"Hello"}]}'

Python

import os
from openai import OpenAI
client = OpenAI(base_url="https://keeprouter.com/v1", api_key=os.environ["KEEPROUTER_KEY"])
r = client.chat.completions.create(model="gemini-3.1-pro-preview-customtools", messages=[{"role":"user","content":"Hello"}])

JavaScript

import OpenAI from "openai";
const client = new OpenAI({ baseURL: "https://keeprouter.com/v1", apiKey: process.env.KEEPROUTER_KEY });
const r = await client.chat.completions.create({ model: "gemini-3.1-pro-preview-customtools", messages: [{ role: "user", content: "Hello" }] });

Estimate API costs

At the current KeepRouter customer price, an example workload of 1,000 total input tokens, no cached input, and 500 output tokens per request costs approximately $0.0130 per request. At 100 requests per day, that is $39.00 over 30 days. This is a usage estimate, excluding processing fees, taxes, retries and application infrastructure. Actual usage, cache hits and supported generation durations need their own checks.

Adjust quantities in the API cost calculator.

Model identity and official sources

Sources checked 2026-10-03.

Model and intended use

Google documents a distinct variant tuned to prioritize custom tools and bash workflows. Retain tool-call IDs and Google thought signatures across turns. Check this exact variant’s current price on its model page.

Google Cloud · model card

Documented limits and tested scope

Google documents a 1,048,576-token context and up to 65,536 output tokens. We verified a small text completion through KeepRouter on September 29, 2026. This does not certify every media input, tool workflow or production capacity. This HTTP model returns text; Gemini Live is a separate API.

Google Cloud · OpenAI compatibility

Customer prices and token usage

Use this page's current KeepRouter input, output and cached-input rates. Completion usage includes reported reasoning tokens once. Compare total spend per accepted result, including retries. The Gemini guide lists exact models and the streaming, JSON and tool checks completed on September 29, 2026.

KeepRouter · Gemini API guide · KeepRouter · cost calculator

Chat API compatibility

Use a KeepRouter key and this public model ID with POST /v1/chat/completions. Google authentication and model mapping are handled by the gateway. The Google Cloud chat route supports streaming but does not expose Responses, Anthropic Messages, Google-native generateContent or Live WebSockets. Other serving routes may differ; consult the exact model's endpoint guidance. This interface guidance was updated on October 3, 2026.

KeepRouter · Gemini API guide

How to evaluate Gemini 3.1 Pro Custom Tools (Preview)

Gemini 3.1 Pro Custom Tools (Preview) is listed on KeepRouter as text, vision, audio, video, pdf under the exact id gemini-3.1-pro-preview-customtools. Use /v1/chat/completions for the listed route; a maker's upstream features do not automatically apply to this gateway endpoint. The published context window is 1,048,576 tokens and the published output limit is 65,536 tokens. These are limits, not a recommended request size.

First workload: Start with a text question plus one representative image, then repeat the same question with text only. Compare answer quality, latency and billed input/output tokens.

Before production: For agent use, test tool calls and structured output on this exact model route before production; an OpenAI-compatible chat endpoint alone does not prove either feature.

Agent setup paths

OpenCode

OpenCode documents a custom OpenAI-compatible provider. Set baseURL to https://keeprouter.com/v1 and list gemini-3.1-pro-preview-customtools as a model; validate tool behavior on the exact route. Official setup.

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "keeprouter": {
      "npm": "@ai-sdk/openai-compatible",
      "name": "KeepRouter",
      "options": {
        "baseURL": "https://keeprouter.com/v1",
        "apiKey": "{env:KEEPROUTER_API_KEY}"
      },
      "models": {
        "gemini-3.1-pro-preview-customtools": {
          "name": "Gemini 3.1 Pro Custom Tools (Preview)"
        }
      }
    }
  }
}

Continue

Continue documents provider: openai with a custom apiBase. Set apiBase to https://keeprouter.com/v1 and model to gemini-3.1-pro-preview-customtools; validate the selected feature and endpoint. Official setup.

name: KeepRouter
version: 0.0.1
schema: v1
models:
  - name: Gemini 3.1 Pro Custom Tools (Preview)
    provider: openai
    model: gemini-3.1-pro-preview-customtools
    apiBase: https://keeprouter.com/v1
    apiKey: <YOUR_KEEPROUTER_API_KEY>

These are documented configuration paths; model-specific tool, streaming and multimodal behavior still needs a real request test.

Public model usage evidence

No public, exact-variant usage figure has been verified for this KeepRouter model id. Missing data is not zero usage; family-level or maker-wide traffic is not presented as this model's traffic.

Published examples and cases

No exact-model customer case has been verified for this entry. The workload above is an evaluation recipe, not a claim of a public deployment.

Source and verification boundary

Official Gemini 3.1 Pro Custom Tools (Preview) documentation. KeepRouter's live catalog is authoritative for the customer price and enabled endpoint shown here; the maker remains authoritative for upstream model capabilities and limits.

Pricing and implementation guides

Guides

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