Quick start

You need Python 3.11+ and at least two supported CLIs installed and signed in: Claude Code, Codex CLI, or opencode.

uv tool install tandem-cli   # or: pip install tandem-cli
cd your-project
tandem

Work normally in the CLI that opens. Press Ctrl-] to continue the same session in the next CLI. If you press it while the model is working, tandem waits until the response finishes; press it again to cancel the switch.

Exit normally when you're done. Come back later with:

tandem resume      # resume the latest session in this directory
tandem sessions    # find recent sessions across directories

By default, tandem opens the first usable CLI in your configured order. Use tandem --active codex or tandem --active opencode to choose another.

What's new in 0.5

Rate-limit windows on the tab bar. Every slot now shows its account's rate limits — percent used per window, labeled by window length — so you can see which subscription has room before you press Ctrl-]. The active slot also carries the model's live context and the session's input↑ / output↓ token totals:

 claude ● 144k ctx · 7.6M↑ 312k↓ · 5h 4% 7d 41% │ codex ○ 7d 12% │ opencode ○   ^] flips

The figures come from the same account endpoints that claude's /usage and codex's /status call, using the credentials those CLIs already keep on disk, refreshed every minute and after each response. They are cosmetic by design: a failed fetch blanks the figure and never touches sync, and API-key logins and opencode show none. These polls are tandem's only network calls — set rate_limits = false under [frame] in ~/.tandem/config.toml to turn them off. See Configuration for the status bar's other settings.

0.5.1 keeps up with the current CLIs. claude 2.1.26x and codex 0.153 changed their session records, and codex now holds a writer lock on every open thread. On those versions 0.5.0 failed tandem doctor and every flip into claude on the new metadata records, warned that codex was out of range at each start, and could lose a claude → codex flip to already has an active writer. All three are fixed, and codex's list-shaped tool outputs now reach the other side as text with their exit codes intact.

0.5.2 stops claude complaining about synced turns. claude 2.1.261 restores a session's model on resume from its last assistant entry, and a claude session that had never run a turn of its own (claude → codex → opencode → claude) opened with Session model <synced> could not be restored … using fable instead. Synced entries now carry claude's own <synthetic> tag until claude has run, which its resume skips; the synced turns still render and still reach the model.

Why tandem?

• Keep going when a model hits its limit. The tab bar shows each account's rate-limit windows; move to another CLI and continue with the same files and conversation history.
• Bring different models to the same problem. Ask another CLI for a second opinion without copying a wall of context between terminals.
• Keep the native tools you already use. Claude Code, Codex, and opencode retain their own interfaces, commands, keybindings, and MCP servers.
• Work through a single-provider outage. If another configured CLI is available, switch and continue until the affected provider recovers.

Want GPT subagents inside Claude Code too? See the GPT subagents guide. For more use cases, see Why tandem?.

How it works

┌──────────────────────────────────────────────┐
│ Work normally in a native coding CLI         │
└──────────────────────┬───────────────────────┘
                       ▼
┌──────────────────────────────────────────────┐
│ tandem keeps the other sessions in sync      │
│ locally — without calling another model      │
└──────────────────────┬───────────────────────┘
                       ▼
┌──────────────────────────────────────────────┐
│ Press Ctrl-] and continue in the next CLI    │
└──────────────────────────────────────────────┘

Only the active model runs. tandem translates its growing conversation into the other CLIs' native session formats using local file access, so they are ready when you switch. Your session stays in the CLIs' own storage plus a small local database in ~/.tandem; tandem adds no cloud sync or telemetry (its only network calls are the optional rate-limit polls for the tab bar).

See How tandem works for transcript translation, switching, crash safety, compatibility, and data locations.

Everyday commands

Learn more

• Why tandem? — use cases, subscriptions, native tools, token visibility, and privacy
• GPT subagents — plugin setup, worker models, routing, and sandboxing
• Configuration — participants, startup arguments, the switch key, and the status bar
• How tandem works — synchronization, switching, compatibility, and local data
• Developing tandem — development setup and the harness adapter interface
• Observed session formats — Claude Code, Codex, and opencode storage formats

License

MIT