mmux vs Codex app

What is the Codex app?

OpenAI released the Codex app for macOS in February 2026 as a place to run several Codex agents in parallel, each in its own chat, organized by project [13]. On July 9, 2026, OpenAI shipped a new ChatGPT desktop app for macOS and Windows that combines Chat, Work and Codex; existing Codex app users move to it by updating [12]. OpenAI's documentation now describes these features under the ChatGPT desktop app [1], with a Windows build from the Microsoft Store [10] and a Linux build in preview for Ubuntu, Debian, Fedora and Arch [11]. This page keeps calling it the Codex app, since that is the part being compared.

A Codex project points at a local folder (or several, with one primary repository) or at a project on an SSH host [8][5]. Each chat can run in the local checkout or in a managed git worktree that Codex creates under $CODEX_HOME/worktrees; Handoff moves a chat and its code between the two, and Codex removes old managed worktrees beyond the 15 most recent after saving a snapshot [2]. Each chat has an integrated terminal scoped to its project or worktree [4], and the review pane shows the diff, takes inline comments for Codex, stages or reverts chunks, commits, pushes and opens pull requests [3]. The app also offers scheduled tasks [6], cloud tasks, notifications when a turn finishes or needs approval [7], and sign-in with a ChatGPT plan or an API key [9].

Where the Codex app is better

• The review loop. You can comment on a diff line and have Codex address it, stage or revert individual chunks, open a pull request and review PRs in a side panel [3][12]. mmux's git panel stages whole files or directories, has no inline comments and does not create pull requests.
• Worktrees with a safety net. Codex snapshots a managed worktree before deleting it and restores it when you reopen the chat, and Handoff moves work between the worktree and your local checkout [2]. mmux removes only finished worktrees whose commits are merged or pushed, but has no snapshot or handoff.
• Work beyond your machine. Codex cloud tasks run in OpenAI's environments, scheduled tasks start chats on a timer [6], and the ChatGPT mobile app can drive a connected Mac or Windows host [5]. mmux runs only where you start it and schedules commits, not agent runs.
• Windows and no terminal required. There is a native Windows app with a Windows sandbox and optional WSL [10], and the whole interface is a desktop GUI. mmux is a TUI for macOS and Linux that needs tmux.
• Built-in sandboxing. The app ships its own sandbox and approval modes (a native Windows sandbox, and bubblewrap when the agent runs in WSL2) [10]. mmux does not sandbox; it starts each agent with that agent's own permission flags.

Where mmux is better

• Any agent, side by side. mmux ships presets for Claude, Codex, Gemini, Amp, opencode, Pi and Grok, and any other command can be an agent. A Claude agent and a Codex agent can work in two worktrees of the same repository in one sidebar, each row turning green when it is done.
• Survives the window and the connection. The TUI runs inside an invisible per-directory tmux session, so closing the terminal or dropping SSH only detaches; mmux attach rejoins from anywhere. After a quit or crash, Claude, Codex, Pi and Grok agents resume their conversations.
• Lives where the code lives. Run mmux on a remote dev box and it keeps working there with nothing attached; under 60 columns it switches to a single-column layout for SSH from a phone, and desktop notifications travel over SSH to the machine your terminal runs on.
• Dev servers as first-class rows. Processes sit in the sidebar with start, stop and a stop: teardown command. Only one checkout of a repository runs a given process at a time, so starting Dev in a worktree stops it in the main clone first and localhost:3000 is always the branch you last started.
• Scriptable by agents. Every running mmux has a control socket: mmux ask, mmux wait, mmux read and mmux worktree new --prompt let one agent start, prompt and read another, visibly in your sidebar.
• Open source, no account. mmux is GPLv3, a single binary, and needs no sign-in of its own.

When to use which

Using the Codex app and mmux together

1. Turn on the Codex preset in mmux with mmux agents (or a in the sidebar), picking the normal, auto or danger mode.
2. Start Codex in its own worktree, from the TUI with w or from a script.
3. When you want the Codex app's review pane or a pull request, add the repository as a local project in the desktop app and review there; mmux's git panel picks up commits made elsewhere on its own.

mmux worktree new fix-auth --agent codex --prompt "fix the login bug"
mmux ask --agent codex "why does /health 500?"