The Codex app runs many Codex agents. Synapse connects Codex to agents from other vendors. The Codex app, now part of the ChatGPT desktop app, gives you parallel chats in local, worktree or cloud mode, native subagents, forking from any message and automations. Its subagents inherit the parent's provider, so every agent in it is OpenAI. Synapse links a running Codex agent to Claude Code, Gemini CLI and others on your machine, injects recent conversation on each prompt, and lets them message each other. Synapse needs no account and makes no network calls. The Codex app is the far more complete product for running Codex.
At a glance
| Synapse | The Codex app | |
|---|---|---|
| What it is | Canvas and messaging layer for every agent on your machine | Desktop app for parallel Codex chats, inside the ChatGPT desktop app since July 2026 |
| Which agents | Claude Code, Codex, Gemini CLI, OpenCode, Cursor Agent, Amp, Copilot CLI | Codex only, OpenAI models only |
| Live context between agents | Yes, directional links, every prompt | Subagents return summaries to the main chat |
| Cross-vendor | Claude to Codex and back, plus others | One-way import from Claude Code, Cowork and Cursor |
| Forks | /sfork, in development (Claude Code and Codex) | Shipped, including fork from an earlier message |
| Worktrees, cloud tasks, automations, PR Chat | No | Yes |
| Account | None | ChatGPT account (API key for CLI, SDK and IDE) |
| License | MIT | Codex CLI is Apache 2.0; we found no public source for the app |
| Platforms | macOS first | macOS, Windows, Linux preview, iOS remote control |
Codex app facts are from the Codex app docs, changelog and pricing page, checked on 16 October 2026. The latest app build in the changelog was 26.1007.
What the Codex app is
OpenAI launched the Codex app for macOS on 2 February 2026, added Windows on 4 March, and on 9 July announced that "Codex is now part of the ChatGPT desktop app on macOS and Windows." A Linux preview of the ChatGPT desktop app followed on 11 August.
Inside it you run parallel chats (formerly threads) across projects. Each chat runs Local, in a Worktree, or in the Cloud. Handoff moves a chat between local and worktree, and since June between local and remote hosts. Around that are Skills, Automations on a schedule, PR Chat for GitHub reviews, Computer Use, SSH remotes, and an iOS app that controls remote hosts.
Simon Willison described it as "a solid app that provides a nice UI over the capabilities of the Codex CLI agent."
What Synapse is
Synapse puts every live coding agent on your machine on one canvas, grouped by git repo. It finds Claude sessions from Claude Code's session registry and every other CLI, Codex included, by scanning processes.
Drag from agent A to agent B and B gets A's context. On each prompt, a hook injects what A said since last time, up to 8,000 characters per link. For Codex, Synapse reads the rollout files on disk. Linked agents can message each other through MCP tools, a CLI and a skill.
How Codex agents work together, and how Synapse links do
Here is what the Codex app does, precisely.
- Subagents are on by default, with built-ins called
default,workerandexplorerand custom agents in TOML. The orchestrator spawns them, routes follow-ups, waits, and "returns a consolidated response". Each subagent thread is visible in the app. Official docs do not describe subagents messaging each other directly. - Separate chats do not talk to each other according to the worktree docs. The changelog for build 26.527 (29 May 2026) mentions "thread coordination for local projects and worktrees", but we did not find documentation of how it works.
- Provider lock. The subagent docs say custom agent files "can't change
model_provider, and subagents inherit the parent's provider."
For other vendors, OpenAI offers two bridges, both one way:
- Import (since June, extended in August) copies instructions, settings, skills, plugins, projects and recent work from Claude Code, Claude Cowork and Cursor into Codex, with optional auto-sync. That is migration, not a live link.
- The Codex plugin for Claude Code (
openai/codex-plugin-cc, Apache 2.0) adds/codex:reviewand/codex:rescueinside Claude Code, handing a task to Codex as a subagent.
Synapse is different:
- A link is live and stays in place. Every time the Codex agent gets a prompt, it sees what the linked Claude Code agent said since last time.
- It works peer to peer, across CLIs. Codex and Claude Code can message each other, and either can message Gemini CLI.
- It is pull based. An idle agent does not wake up on its own.
OpenAI removed the standalone codex mcp-server on 5 September 2026. Synapse does not depend on it: it wires its own MCP server and prompt hook into the Codex CLI and reads rollouts from disk.
Forks
The Codex app shipped conversation forking on 12 February 2026 and forking from an earlier message on 18 March. Forks appear as separate chats. The iOS app can fork tasks too.
Synapse's forks are in development in its desktop app. They call the native command (codex fork <id>, or the Claude Code equivalent) after you type /sfork <question> or press ⇧⌘F. The fork becomes a card stacked on its parent, so the side question never enters the parent's context, and the lineage shows on the canvas. Codex's own forking is shipped and works today.
Accounts, privacy and lock-in
You sign in to the Codex app with a ChatGPT account. The CLI, SDK and IDE can use an API key, though cloud features like GitHub review and Slack are not included with one. Per the pricing page, plans run from Free and Go ($8 a month, both "subject to rollout") to Plus at $20, Pro from $100, and Business at $25 per user per month ($20 billed annually). Usage limits are estimated per 5-hour window.
The July merge into ChatGPT was not universally welcome. In a Hacker News thread titled "Tell HN: The Codex App is replaced by ChatGPT", the author said they "cannot mix my personal and work use" in one app. If you keep work and personal accounts apart, that is worth knowing.
Synapse has no account. Links and messages live in ~/.synapse, and it makes no network calls.
Where the Codex app is ahead
- A full workspace. Worktree lifecycle with snapshots, handoff between local, worktree and remote, cloud tasks, Automations, PR Chat and Computer Use. Synapse has none of these.
- Native subagents and forking. Both shipped, both inside the app. Synapse's forks are in development.
- Cross-device today. Codex Remote has been generally available since 25 June 2026, with iOS control. Synapse multiplayer is not shipped.
- Platforms and maturity. macOS, Windows and a Linux preview, backed by OpenAI. Synapse is new, built in October 2026 and macOS first.
Using Synapse with the Codex app
Synapse discovers Codex CLI processes, so use the CLI for the agents you want to link:
- Install Synapse: clone the repo, run
node install.mjs && npm start. - Restart running Codex sessions, and approve the hook once when Codex asks.
- Open the canvas at localhost:4747. Codex and Claude Code agents show up as nodes, grouped by repo.
- Drag a link from Claude Code to Codex so Codex sees Claude's plan on every prompt. Draw the reverse link if Claude should see what Codex changed.
- Keep long unattended work in the Codex app's cloud tasks. Use Synapse links for interactive pairing, such as Claude planning, Codex implementing and Gemini CLI reviewing.
Who should pick which
- Pick the Codex app if Codex is your only agent and you want worktrees, cloud tasks, automations and PR review in one place.
- Add Synapse if you run Codex next to Claude Code or Gemini CLI and want them to share context and message each other without copy and paste.
- Use both when you have both needs. Synapse does not replace where Codex runs.
FAQ
Is the Codex app still a separate app?
No. On 9 July 2026 OpenAI announced that Codex is now part of the ChatGPT desktop app on macOS and Windows. A Linux preview of the ChatGPT desktop app followed in August 2026.
Can Codex subagents use Claude or other models?
No. The Codex subagent docs say custom agent files can't change the model provider and subagents inherit the parent's provider. Synapse can link a Codex agent to a separate Claude Code agent so each sees the other's recent work.
How do I use Codex and Claude Code together?
Install Synapse, restart both agents, and link them on the canvas. The receiving agent gets the other's recent conversation on each prompt, and both can message each other. OpenAI's Codex plugin for Claude Code hands tasks from Claude to Codex one way.
Can I fork a conversation in the Codex app?
Yes. The Codex app has shipped conversation forking since February 2026 and forking from an earlier message since March 2026. Synapse's /sfork, which stacks forks on their parent and draws the tree on a canvas, is in development for Codex and Claude Code.
Is Synapse a Codex app alternative?
Not for running Codex. Synapse has no worktree management, cloud tasks or PR review. It is the layer that lets a Codex agent share context and messages with agents from other vendors.
Does Synapse need a ChatGPT account?
Synapse itself needs no account and makes no network calls. Your Codex CLI still uses whatever ChatGPT sign-in or API key it already has.