# Google Gemini 3.1 Pro Preview Custom Tools API

> Gemini 3.1 Pro Preview Custom Tools is a separate endpoint of Google's Gemini 3.1 Pro Preview, the Pro-tier reasoning model of the Gemini 3 series, tuned for agentic workflows that mix bash with custom tools. Google says it is better at prioritizing user-defined functions, such as file viewing or code search tools, over a general bash tool. Pick it for coding agents built on custom tools; Google notes quality may fluctuate in use cases that do not benefit from such tools, where the standard 3.1 Pro Preview fits better.

Source: https://www.sandbase.ai/models/google/gemini-3.1-pro-preview-customtools
API reference: https://www.sandbase.ai/models/google/gemini-3.1-pro-preview-customtools/docs

## Facts

- Provider: Google
- Type: Language model
- Model ID: `google/gemini-3.1-pro-preview-customtools`
- Price: $1.70 per 1M input tokens, $10.20 per 1M output tokens (15% off list price)
- Context window: 1M tokens, up to 65.5K output tokens
- Capabilities: chat, vision, audio input, reasoning, structured output, function calling
- Billing: pay per use from one SandBase balance; no provider account or subscription needed

## Call it

- Chat Completions API: `POST https://api.sandbase.ai/v1/chat/completions`

```bash
curl -X POST https://api.sandbase.ai/v1/chat/completions \
  -H "Authorization: Bearer $SANDBASE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "google/gemini-3.1-pro-preview-customtools",
  "messages": [
    {
      "role": "user",
      "content": "Hello"
    }
  ],
  "max_tokens": 2048
}'
```

## FAQ

### How do I call Google Gemini 3.1 Pro Preview Custom Tools through SandBase?

Create a SandBase API key, then send requests with the model ID "google/gemini-3.1-pro-preview-customtools" to Chat Completions API (/v1/chat/completions) at https://api.sandbase.ai. The request examples on this page show the exact payload.

### How much does Google Gemini 3.1 Pro Preview Custom Tools cost?

$1.70 per 1M input tokens and $10.20 per 1M output tokens with the current 15% discount (list price $2 / $12), billed per request from your SandBase balance.

### What is the context window of Google Gemini 3.1 Pro Preview Custom Tools?

1M tokens of context, with up to 65.5K output tokens per response.

### How does Google Gemini 3.1 Pro Preview Custom Tools score on benchmarks?

Google Gemini 3.1 Pro Preview Custom Tools scores 29.7 on the Artificial Analysis Intelligence Index (v4.3), ranking #42 of 83 models on SandBase; Coding Index 68.8, Agentic Index 8.2. Source: Artificial Analysis, measured as Gemini 3.1 Pro Preview.

### Which features does Google Gemini 3.1 Pro Preview Custom Tools support?

Google Gemini 3.1 Pro Preview Custom Tools supports vision (image input), reasoning, function calling, structured output. See Specifications above for the full list.

### Do I need a separate Google account?

No. One SandBase API key and balance gives you access to Google Gemini 3.1 Pro Preview Custom Tools and the other models in the catalog; you do not need to sign up with Google separately.