> ## Documentation Index
> Fetch the complete documentation index at: https://allhandsai-feature-use-case-docs.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# ACP Agents

> Drive Agent Canvas conversations with an external coding agent — Claude Code, Codex, or Gemini CLI — over the Agent Client Protocol.

Agent Canvas can drive your conversations with the built-in **OpenHands** agent or with an external **ACP agent** — Claude Code, Codex, or Gemini CLI. This guide explains what ACP agents are, how to onboard one, and how to switch agents or models later.

## What is an ACP agent?

The [Agent Client Protocol (ACP)](https://agentclientprotocol.com/protocol/overview) is a standard for talking to coding agents over JSON-RPC on stdio. Instead of Agent Canvas calling an LLM directly, the Agent Server spawns the agent's own CLI as a subprocess and relays each turn to it. The external agent manages its own LLM, tools, and execution; Agent Canvas sends messages and renders what comes back.

```mermaid theme={null}
flowchart LR
    canvas["Agent Canvas<br/>(this UI)"]
    server["Agent Server"]
    acp["ACP subprocess<br/>(e.g. claude-agent-acp)"]
    llm["LLM provider<br/>(Anthropic / OpenAI / Google)"]
    canvas -- "PATCH /api/settings<br/>(agent_kind, acp_*)" --> server
    canvas -- "conversation turns" --> server
    server -- "spawn + JSON-RPC over stdio" --> acp
    acp -- "API calls" --> llm
```

The Agent Server owns the subprocess and the credentials; Agent Canvas only records *which* agent to run and surfaces a form for the secrets it needs. The agent choice is stored per backend, so switching backends can switch agents.

## Supported providers

| Provider        | Default command                                |
| --------------- | ---------------------------------------------- |
| **Claude Code** | `npx -y @agentclientprotocol/claude-agent-acp` |
| **Codex**       | `npx -y @zed-industries/codex-acp`             |
| **Gemini CLI**  | `npx -y @google/gemini-cli --acp`              |

The provider list is sourced from the OpenHands SDK registry (`openhands.sdk.settings.acp_providers`, mirrored into `@openhands/typescript-client`) and enriched with Canvas UI metadata. Adding or changing a provider happens upstream in the SDK.

## Authentication

<Info>
  ACP agents authenticate **two ways: a subscription login, or an API key** — and the onboarding fields are optional. If you're already signed in to the provider's CLI on the machine the agent runs on, it reuses that login automatically, so locally you often don't need a key at all. **The login takes priority over an API key:** while you're signed in, a key set in the environment isn't used — so the onboarding key fields do nothing and can be left blank.
</Info>

A "subscription login" is the credential the provider's own CLI stores when you sign in once — a file in your home directory, or, for Claude Code on macOS, the system **Keychain**. When the Agent Server runs **on that same machine** (a local or self-hosted backend), the provider CLI finds that login automatically — no API key required. On a clean cloud sandbox there's no stored login, so an API key is needed instead.

| Provider        | Subscription login (auto-detected)                                                                                                        | API key             |
| --------------- | ----------------------------------------------------------------------------------------------------------------------------------------- | ------------------- |
| **Claude Code** | A Claude Code login (Pro/Max), from Claude Code's own credential store: the **macOS Keychain**, or `~/.claude/.credentials.json` on Linux | `ANTHROPIC_API_KEY` |
| **Codex**       | A ChatGPT login (`codex login`) cached at `~/.codex/auth.json`                                                                            | `OPENAI_API_KEY`    |
| **Gemini CLI**  | Your Google login (`gemini`/`gemini --acp`) cached at `~/.gemini/oauth_creds.json`                                                        | `GEMINI_API_KEY`    |

All three collect an *optional* API key (plus base URL) in onboarding. As noted above, a subscription / OAuth login takes priority over an API key — when the provider's CLI is signed in, a key set in the environment is not used:

* **Codex** — `codex login status` keeps reporting the ChatGPT login even with `OPENAI_API_KEY` set.
* **Gemini CLI** — uses the OAuth auth type chosen at `gemini` login; `GEMINI_API_KEY` is only consulted if you switch the auth type. The free Google login is the common no-key path locally — sign in once and it just works.
* **Claude Code** — with both present, `claude auth status` reports it is authenticated via the subscription (`claude.ai`), not the key. The login is auto-detected from the macOS Keychain (or `~/.claude/.credentials.json` on Linux); `CLAUDE_CONFIG_DIR` is **not** required for it — it only relocates Claude Code's config directory (settings/history, not the token) and signals the SDK to strip a conflicting `ANTHROPIC_API_KEY` / `ANTHROPIC_BASE_URL`.

The one exception is the **base URL** (`*_BASE_URL`): a custom value points the CLI at a different endpoint (a proxy or gateway) and *does* take effect even under a login — for Gemini it rides the ACP `gateway` param. It's an advanced override, not needed for normal use.

## Onboarding an ACP agent

First-time users get a four-step onboarding modal. To onboard an ACP agent:

1. **Choose agent** — pick Claude Code, Codex, or Gemini CLI instead of OpenHands. The choice is saved immediately to your backend's settings.
2. **Check backend** — confirms Agent Canvas can reach the Agent Server.
3. **Set up credentials** — enter the provider's API key (and, optionally, a custom base URL for a proxy or gateway). All three providers collect these here, and every field is optional.
4. **Say hello** — creates your first conversation and closes the modal.

<Note>
  Every credential field is optional and the step is skippable. Leave a field blank to reuse a key already set on the backend, or to authenticate the agent through a subscription / OAuth login instead.
</Note>

### How credentials reach the agent

Each credential you enter is saved as a **global secret** whose name is exactly the environment variable the Agent Server exports into the ACP subprocess (e.g. `ANTHROPIC_API_KEY`). Saving in onboarding is identical to adding the secret under **Settings → Secrets**, where you can edit or remove it anytime. Keeping the secret name equal to the env var is what makes a saved key actually reach the provider CLI.

## Switching agent or model later

Open **Settings → Agent** at any time:

* **Agent** — switch between **OpenHands** and **ACP**.
* **Preset** — pick a built-in provider (Claude Code, Codex, Gemini CLI) or **Custom** to point at any other ACP server.
* **Command** — the command line used to spawn the subprocess. Selecting a preset fills this in; editing it to match another preset re-detects that provider. API keys are *not* entered here — they live in the Secrets panel.
* **Model** — choose a suggested model for the provider or enter a custom model override. Built-in providers save a concrete model rather than leaving it blank.

Saving writes an `agent_settings_diff` (`agent_kind`, `acp_server`, `acp_command`, `acp_model`) to `PATCH /api/settings`. A running conversation keeps the agent it started with; the new choice applies to conversations you start afterward.

## Custom ACP servers

Any stdio ACP server works: choose **Custom** in Settings → Agent and enter its launch command. Custom servers have no curated model list, so enter the model ID the server expects (if any) as a custom model. Pass credentials by adding the env vars the server reads as global secrets under **Settings → Secrets**.

## Related Guides

* [Customize and Settings](/openhands/usage/agent-canvas/customize-and-settings)
* [LLM Profiles and Model Configuration](/openhands/usage/agent-canvas/llm-profiles)
* [Connect and Manage Backends](/openhands/usage/agent-canvas/backends)