Agent runtimes

An agent runtime is the component that owns one prepared model loop: it receives the prompt, drives model output, handles native tool calls, and returns the finished turn to OpenClaw.

Runtimes are easy to confuse with providers because both show up near model configuration. They are different layers:

You will also see the word harness in code. A harness is the implementation that provides an agent runtime. For example, the bundled Codex harness implements the codex runtime. Public config uses agentRuntime.id; openclaw doctor --fix rewrites older runtime-policy keys to that shape.

There are two runtime families:

• Embedded harnesses run inside OpenClaw's prepared agent loop. Today this is the built-in pi runtime plus registered plugin harnesses such as codex.
• CLI backends run a local CLI process while keeping the model ref canonical. For example, anthropic/claude-opus-4-7 with agentRuntime.id: "claude-cli" means "select the Anthropic model, execute through Claude CLI." claude-cli is not an embedded harness id and must not be passed to AgentHarness selection.

Codex surfaces

Most confusion comes from several different surfaces sharing the Codex name:

Those surfaces are intentionally independent. Enabling the codex plugin makes the native app-server features available; it does not rewrite openai-codex/* into openai/*, does not change existing sessions, and does not make ACP the Codex default. Selecting openai-codex/* means "use the Codex OAuth provider route" unless you separately force a runtime.

The common ChatGPT/Codex subscription setup uses Codex OAuth for auth, but keeps the model ref as openai/* and selects the codex runtime:

{
  agents: {
    defaults: {
      model: "openai/gpt-5.5",
      agentRuntime: {
        id: "codex",
      },
    },
  },
}

That means OpenClaw selects an OpenAI model ref, then asks the Codex app-server runtime to run the embedded agent turn. It does not mean "use API billing," and it does not mean the channel, model provider catalog, or OpenClaw session store becomes Codex.

When the bundled codex plugin is enabled, natural-language Codex control should use the native /codex command surface (/codex bind, /codex threads, /codex resume, /codex steer, /codex stop) instead of ACP. Use ACP for Codex only when the user explicitly asks for ACP/acpx or is testing the ACP adapter path. Claude Code, Gemini CLI, OpenCode, Cursor, and similar external harnesses still use ACP.

This is the agent-facing decision tree:

1. If the user asks for Codex bind/control/thread/resume/steer/stop, use the native /codex command surface when the bundled codex plugin is enabled.
2. If the user asks for Codex as the embedded runtime or wants the normal subscription-backed Codex agent experience, use openai/<model> with agentRuntime.id: "codex".
3. If the user asks for Codex OAuth/subscription auth on the normal OpenClaw runner, use openai-codex/<model> and leave the runtime as PI.
4. If the user explicitly says ACP, acpx, or Codex ACP adapter, use ACP with runtime: "acp" and agentId: "codex".
5. If the request is for Claude Code, Gemini CLI, OpenCode, Cursor, Droid, or another external harness, use ACP/acpx, not the native sub-agent runtime.

For the OpenAI-family prefix split, see OpenAI and Model providers. For the Codex runtime support contract, see Codex harness.

Runtime ownership

Different runtimes own different amounts of the loop.

This ownership split is the main design rule:

• If OpenClaw owns the surface, OpenClaw can provide normal plugin hook behavior.
• If the native runtime owns the surface, OpenClaw needs runtime events or native hooks.
• If the native runtime owns canonical thread state, OpenClaw should mirror and project context, not rewrite unsupported internals.

Runtime selection

OpenClaw chooses an embedded runtime after provider and model resolution:

1. A session's recorded runtime wins. Config changes do not hot-switch an existing transcript to a different native thread system.
2. OPENCLAW_AGENT_RUNTIME=<id> forces that runtime for new or reset sessions.
3. agents.defaults.agentRuntime.id or agents.list[].agentRuntime.id can set auto, pi, a registered embedded harness id such as codex, or a supported CLI backend alias such as claude-cli.
4. In auto mode, registered plugin runtimes can claim supported provider/model pairs.
5. If no runtime claims a turn in auto mode, OpenClaw uses PI as the compatibility runtime. Use an explicit runtime id when the run must be strict.

Explicit plugin runtimes fail closed. For example, agentRuntime.id: "codex" means Codex or a clear selection/runtime error; it is never silently routed back to PI.

CLI backend aliases are different from embedded harness ids. The preferred Claude CLI form is:

{
  agents: {
    defaults: {
      model: "anthropic/claude-opus-4-7",
      agentRuntime: { id: "claude-cli" },
    },
  },
}

Legacy refs such as claude-cli/claude-opus-4-7 remain supported for compatibility, but new config should keep the provider/model canonical and put the execution backend in agentRuntime.id.

auto mode is intentionally conservative. Plugin runtimes can claim provider/model pairs they understand, but the Codex plugin does not claim the openai-codex provider in auto mode. That keeps openai-codex/* as the explicit PI Codex OAuth route and avoids silently moving subscription-auth configs onto the native app-server harness.

If openclaw doctor warns that the codex plugin is enabled while openai-codex/* still routes through PI, treat that as a diagnosis, not a migration. Keep the config unchanged when PI Codex OAuth is what you want. Switch to openai/<model> plus agentRuntime.id: "codex" only when you want native Codex app-server execution.

Compatibility contract

When a runtime is not PI, it should document what OpenClaw surfaces it supports. Use this shape for runtime docs:

The Codex runtime support contract is documented in Codex harness.

Status labels

Status output may show both Execution and Runtime labels. Read them as diagnostics, not as provider names.

• A model ref such as openai/gpt-5.5 tells you the selected provider/model.
• A runtime id such as codex tells you which loop is executing the turn.
• A channel label such as Telegram or Discord tells you where the conversation is happening.

If a session still shows PI after changing runtime config, start a new session with /new or clear the current one with /reset. Existing sessions keep their recorded runtime so a transcript is not replayed through two incompatible native session systems.

Related

• Codex harness
• OpenAI
• Agent harness plugins
• Agent loop
• Models
• Status