> ## Documentation Index
> Fetch the complete documentation index at: https://docs.modelstack.cc/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

> ModelStack is a unified AI model API gateway that gives you access to 40+ models from Anthropic, OpenAI, and Google through a single, OpenAI-compatible API.

## What is ModelStack?

ModelStack is a unified API gateway for AI models. Instead of managing separate API keys, SDKs, and billing accounts for each AI provider, ModelStack gives you one API, one key, and one bill.

## Key Features

<CardGroup cols={2}>
  <Card title="Unified API" icon="plug">
    Access Claude, GPT, Gemini, and more through a single OpenAI-compatible endpoint. Switch models by changing one parameter.
  </Card>

  <Card title="40+ Models" icon="brain">
    Anthropic Claude (Opus, Sonnet, Haiku), OpenAI GPT-4o, o1, o3, o4, and Google Gemini 2.5 — all available instantly.
  </Card>

  <Card title="Simple Billing" icon="credit-card">
    Subscription plans with auto-refilling credits every 5 hours. Purchase lifetime credits for additional usage with plan-based discounts.
  </Card>

  <Card title="Dashboard & Analytics" icon="chart-line">
    Real-time usage analytics, request logs, model breakdown charts, and API key management from a single dashboard.
  </Card>
</CardGroup>

## How It Works

1. **Sign up** at [modelstack.cc](https://modelstack.cc/sign-up) and choose a plan
2. **Create an API key** from your dashboard
3. **Make requests** to `api.modelstack.cc` using any OpenAI-compatible SDK
4. **Switch models** freely — just change the `model` parameter

```bash theme={null}
curl https://api.modelstack.cc/v1/chat/completions \
  -H "Authorization: Bearer your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5",
    "messages": [{"role": "user", "content": "Hello!"}]
  }'
```

## Why ModelStack?

* **No provider lock-in** — switch between Anthropic, OpenAI, and Google models with zero code changes
* **OpenAI-compatible** — works with existing OpenAI SDKs in Python, Node.js, and any language
* **Predictable costs** — subscription credits refill every 5 hours; lifetime credits never expire
* **Built for developers** — simple REST API, streaming support, comprehensive error codes