OpenAI documented the Codex App Server, the JSON-RPC layer every Codex surface actually runs on.

CLI, IDE extension, macOS app, and Codex Web all sit on the same harness, linked by a bidirectional JSON-RPC-over-stdio process that hosts core threads and translates client requests into Codex operations. Partners have written clients in Go, Python, TypeScript, Swift, and Kotlin, and TypeScript definitions generate straight from the Rust protocol. OpenAI OpenAI names App Server the first-class integration path it will maintain and refactored its own TUI onto it, which unlocks running the agent on a remote machine while the laptop sleeps.