Claude Code + Codex Side-by-Side

Athena supports both Claude Code and OpenAI Codex as production harnesses. The same workflows run on both — the harness abstraction normalizes events so plugins and the UI behave identically.

Feature Comparison

Switching Harnesses

Set the harness in your config:

// ~/.config/athena/config.json
{
  "harness": "openai-codex"
}

Or select it during the setup wizard:

athena-flow setup

Integration Differences

Claude Code — Uses hook-forwarding over a Unix Domain Socket. The athena-hook-forwarder binary receives hook events from Claude Code's hooks system and streams NDJSON to the runtime.

OpenAI Codex — Uses a JSON-RPC app-server protocol. Events from Codex are translated to Athena's RuntimeEvent schema via a comprehensive event translation layer. Codex uses a persistent thread conversation model with turn-based session management.

Both produce the same normalized event stream. The UI, plugins, and workflows see identical RuntimeEvent objects.

Same Workflow, Two Harnesses

A workflow runs identically on both:

{
  "name": "e2e-test-builder",
  "plugins": ["e2e-test-builder@lespaceman/athena-workflow-marketplace"],
  "promptTemplate": "Add E2E tests...",
  "loop": { "enabled": true, "completionMarker": "ATHENA_COMPLETE", "maxIterations": 10 },
  "isolation": "minimal"
}

No workflow changes needed when switching harnesses. The prompt template, loop logic, plugin loading, and MCP servers all work the same.

Prerequisites

Claude Code:

• claude binary on PATH
• Authenticated

OpenAI Codex:

• codex binary on PATH (minimum version 0.37.0)
• Authenticated

Recommendation

Both harnesses are production-ready. Choose based on your preferred agent runtime. Workflow definitions are portable across harnesses — you can switch at any time without modifying your workflows or plugins.