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

# Supported APIs

> API compatibility layers, agent harness support, and example requests for the LLM Gateway.

## Overview

The LLM Gateway exposes one gateway URL, `https://llm-gateway.aptible.com`, and speaks several API dialects from it. Pick whichever matches how you're already integrating:

* **OpenAI-compatible** — Chat Completions, Responses, and Embeddings, in both a strict `/openai` namespace and as un-namespaced defaults
* **Anthropic-compatible** — Messages, in a strict `/anthropic` namespace
* **Agent harnesses** — a dedicated, never-changing base URL per supported coding assistant or agent harness, under `/harness/<name>`

Every request authenticates with an [LLM Key](/docs/llm-gateway/llm-keys) and selects a model by name in the request body — see [Supported Models](/docs/llm-gateway/supported-models) for the current model catalog.

## Authentication

Send your LLM Key as a bearer token:

```text theme={null}
Authorization: Bearer <YOUR_LLM_KEY>
```

Anthropic's SDKs (and Claude Code) instead send an `x-api-key` header — the gateway accepts either:

```text theme={null}
x-api-key: <YOUR_LLM_KEY>
```

## OpenAI-compatible API

Use the `/openai` namespace for strict OpenAI compatibility:

| Endpoint         | Path                               |
| ---------------- | ---------------------------------- |
| Chat Completions | `POST /openai/v1/chat/completions` |
| Responses        | `POST /openai/v1/responses`        |
| Embeddings       | `POST /openai/v1/embeddings`       |

The same three endpoints are also available un-namespaced (`/v1/chat/completions`, `/v1/responses`, `/v1/embeddings`) as the gateway's default dialect — use whichever your SDK or tooling expects.

For full request and response documentation, see [OpenAI's API reference](https://developers.openai.com/api/reference/overview).

## Anthropic-compatible API

Use the `/anthropic` namespace for Anthropic Messages:

| Endpoint     | Path                                       |
| ------------ | ------------------------------------------ |
| Messages     | `POST /anthropic/v1/messages`              |
| Count Tokens | `POST /anthropic/v1/messages/count_tokens` |

For full request and response documentation, see [Anthropic's API reference](https://platform.claude.com/docs/en/api/overview).

## Agent harness support

Some coding assistants and agent harnesses need a single base URL they can be pointed at once and never have to edit again — even as the underlying API dialect they speak evolves. The LLM Gateway provides one under `/harness/<name>`, which resolves internally to the right compatibility endpoint:

| Harness        | Base URL                                                 |
| -------------- | -------------------------------------------------------- |
| Claude Code    | `https://llm-gateway.aptible.com/harness/claude-code`    |
| Claude Desktop | `https://llm-gateway.aptible.com/harness/claude-desktop` |
| Grok Build     | `https://llm-gateway.aptible.com/harness/grok-build`     |
| Pi             | `https://llm-gateway.aptible.com/harness/pi`             |

See the [Claude Code guide](/docs/getting-started/secure-llm-usage/claude-code) for a full walkthrough of harness setup.

<Info>
  Don't see your harness or coding assistant listed? Any tool that speaks OpenAI- or Anthropic-compatible APIs already works against the `/openai` or `/anthropic` endpoints above — a dedicated `/harness` route just saves you from ever having to change the base URL again. [Contact us](https://app.aptible.com/support) if you'd like a harness added.
</Info>

## Example requests

Every example below uses the model field to select a model — see [Supported Models](/docs/llm-gateway/supported-models) for valid IDs.

<CodeGroup>
  ```bash Chat Completions theme={null}
  curl https://llm-gateway.aptible.com/openai/v1/chat/completions \
    -H "Authorization: Bearer $LLM_GATEWAY_KEY" \
    -H "Content-Type: application/json" \
    -d '{
      "model": "gpt-5",
      "messages": [
        {"role": "user", "content": "Tell me a joke about cloud security"}
      ]
    }'
  ```

  ```bash Responses theme={null}
  curl https://llm-gateway.aptible.com/openai/v1/responses \
    -H "Authorization: Bearer $LLM_GATEWAY_KEY" \
    -H "Content-Type: application/json" \
    -d '{
      "model": "gpt-5",
      "input": "Tell me a joke about cloud security"
    }'
  ```

  ```bash Anthropic Messages theme={null}
  curl https://llm-gateway.aptible.com/anthropic/v1/messages \
    -H "x-api-key: $LLM_GATEWAY_KEY" \
    -H "anthropic-version: 2023-06-01" \
    -H "Content-Type: application/json" \
    -d '{
      "model": "claude-sonnet-5",
      "max_tokens": 1024,
      "messages": [
        {"role": "user", "content": "Tell me a joke about cloud security"}
      ]
    }'
  ```
</CodeGroup>

## Automatic provider failover and client-side fallbacks

If a model is available from more than one provider, the gateway automatically fails over to another available provider during an outage — no client changes required. You can also specify your own fallback models in a request; see [Supported Models](/docs/llm-gateway/supported-models#provider-failover) for details on both.