OpenAI dropped a deep dive on the Codex App Server, the middleware that powers Codex across web, CLI, VS Code, JetBrains, Xcode, and the new macOS app. Instead of building a separate agent loop for each interface, they created a single JSON-RPC API that any client can talk to. This lets the same harness handle everything from streaming reasoning steps to generating diffs. The App Server started as a hack to reuse code between the TUI and VS Code. As demand grew from partners like JetBrains, they hardened it into a stable, backward-compatible protocol. The protocol supports bidirectional messaging, so clients can send live feedback while the agent works. OpenAI also highlights patterns beyond a simple chat: you can wire Codex as a code reviewer, an SRE agent, or a full IDE assistant. Why it matters: This move signals that OpenAI sees Codex as a platform play, not just a standalone tool, making it easier for third-party dev tools to embed agentic coding without reinventing the loop.