OpenAI Codex release notes: replace mcp-server with app server

On August 24, OpenAI deprecated the codex mcp-server command. Integrations that start Codex as an MCP server should move to the Codex app server. For Claude Code, OpenAI recommends the dedicated Codex plugin instead.

MCP, the Model Context Protocol, is a protocol for connecting AI clients to tools and context. The Codex app server is Codex's client-integration interface for authentication, conversation history, approvals, and streamed agent events.

Source: OpenAI Codex changelog, August 24, 2026.

OpenAI Codex release notes: replace mcp-server

OpenAI names two replacements:

• Custom client integrations should use the Codex app server.
• Claude Code users should use the Codex plugin for Claude Code.

The changelog does not give a removal date for codex mcp-server. Treat this as a migration notice rather than a claim that existing calls have already stopped working.

Human step: move a custom integration to app server

Start the app server with its default stdio transport, which uses newline-delimited JSON:

codex app-server

The client must send initialize followed by the initialized notification before it can start threads and turns. OpenAI recommends the Codex SDK instead of app server for automated jobs and CI.

The app server command and WebSocket transport are experimental and unsupported for production workloads. OpenAI documents local WebSocket and Unix-socket options for development and remote terminal use, but a production migration needs to account for those limits.

Source: OpenAI Codex app server documentation.

Human step: use the Codex plugin in Claude Code

Run these slash commands in Claude Code:

/plugin marketplace add openai/codex-plugin-cc
/plugin install codex@openai-codex
/reload-plugins
/codex:setup

The plugin uses the local Codex installation, the same authentication, and the same config.toml. It requires Node.js 18.18 or later plus a ChatGPT subscription, including Free, or an OpenAI API key. After installation, Claude Code can run a read-only Codex review with /codex:review and manage background jobs with /codex:status and /codex:result.

Source: OpenAI Codex plugin for Claude Code.