T3 Code Provider

What it is

T3 Code is an open-source app from the T3 team that runs the coding agents you already have signed in. Omniscio drives it through T3's own documented host command, t3 thread, which needs no sign-in on your own computer.

• One session = one T3 thread. The first message starts a thread; every later message goes to the same thread, including after Omniscio restarts. The thread also shows up in T3 Code itself.
• It uses your own T3. Omniscio holds no T3 password or token. The agent T3 runs uses the login you gave that agent (for example claude auth login, or codex login).

Where to find it

1. Install T3 Code: irm https://t3.codes/install.ps1 | iex on Windows, or curl -fsSL https://t3.codes/install.sh | sh on Mac/Linux. The installer puts t3 in ~/.local/bin; Omniscio finds it there even when that folder is not on your PATH.
2. Turn on Settings → Accounts → T3 Code → Allow T3 Code sessions. It is off by default.
3. Pick T3 Code in a new session's engine picker, or as a project's default engine.

How it behaves

Choosing the model

A fresh session shows a model picker of agent/model pairs — Claude models (claudeAgent/…), Codex models (codex/…) and Antigravity models (antigravity/…). The pick is passed to T3 as its --provider and --model. With no pick the default is claudeAgent/claude-opus-5-5, T3's own default chat model. The agent behind the pick must be installed and signed in on this computer.

What happens when you send

• If no T3 Code server is running, Omniscio starts one out of sight (t3 serve --no-browser), waits until it answers, and reuses one you already run (the T3 desktop app, for example). It stops only a server it started itself, when Omniscio quits. The server's one-time pairing code is never logged.
• On the first message the session's folder is added as a T3 project if T3 does not know it yet. A folder inside an existing T3 project belongs to that project, and T3 runs the agent at that project's root.
• The reply arrives in one piece when T3's turn finishes. While it works the session stays live.
• A message sent while T3 is still busy is queued by T3 as the next turn; nothing is interrupted.

Waiting, stopping and errors

• T3 Code is waiting for your answer — the agent stopped to ask you something inside T3. The session shows that line with a link that opens the thread in T3 Code.
• Stop pressed before the message reaches T3 (while its server is starting, or while the folder is being added) means the message is never sent. Pressed after, it ends Omniscio's wait: T3 has no stop command, so that turn may still finish inside T3 Code, and the thread link shows it.
• Recheck on the settings card does not pick up a fresh install until Omniscio restarts, the same as Muse Code; the card says so.
• Failures read as one sentence naming T3 Code and T3's own reason — for example "T3 Code couldn't finish this turn: Failed to authenticate…" when the agent behind the pick is not signed in. "T3 Code is not installed" and "T3 Code's server would not start" are Omniscio's own sentences.

Limits in this version

• Text-only: an attached image shows a warning instead of reaching the agent.
• Cost shows as not reported — T3 reports no spend.
• Every tool the agent runs is auto-approved: threads started from T3's command line run in T3's full-access mode. That is why the switch is off by default and the settings card warns about it.
• Sessions run in an isolated worktree when isolation is on, like the other auto-approve engines.
• No SSH-remote or cloud sessions.

How it works under the hood

Part	File
Engine declaration, readiness, setup card, model list	src/shared/providers/registry.ts, provider-setup-catalog.ts, provider-models.ts
Finds t3 (PATH, then ~/.local/bin/t3.cmd, followed to the real t3.exe)	src/main/services/engines/t3code-binary-resolver.ts
Runs one t3 command (quiet logs, prompt on stdin, kill job)	src/main/services/engines/t3code-cli.ts
Starts / reuses the T3 server, cleaned environment	src/main/services/engines/t3code-server.ts
Adds the folder as a T3 project when missing	src/main/services/engines/t3code-project.ts
One turn: start or send without waiting, save the thread id at once, poll thread show until the run settles	src/main/services/engines/t3code-turn-runner.ts
The session manager on the shared one-shot base	src/main/services/engines/t3code-session-manager.ts

The thread id is saved the moment t3 thread start answers, before the turn is waited on, so stopping or quitting during the very first turn still continues the same thread next time. A run counts as finished only once T3 no longer reports it active and its status has left starting / queued / running / waiting; a run queued behind a busy thread keeps waiting. The prompt pipe is guarded, so a t3 that exits before reading it cannot crash the app.

Contract: provider-registry-engines-more-t3code-shot-cli-contract.md.