Hosting a runtime

constant host runs one agent CLI inside a native PTY and lets you switch the live runtime with a tmux-style prefix key, mid-conversation.

constant host codex
constant host claude

The child keeps its own terminal UI, colors, keybindings, and resume behavior. Constant sits outside it, forwards input and output untouched, and only steps in when it sees the prefix key.

Switching

The default prefix is Ctrl-B. Press it, release, then a key:

Keys	Action
`Ctrl-B` `c`	Continue in Claude Code, refreshing the existing projection
`Ctrl-B` `C`	Create a new Claude continuation
`Ctrl-B` `x`	Continue in Codex, refreshing the existing projection
`Ctrl-B` `X`	Create a new Codex continuation
`Ctrl-B` `:`	Open the Constant command line (`switch`, `new`, `quit`)
`Ctrl-B` `d`	Detach and exit cleanly
`Ctrl-B` `Ctrl-B`	Send a literal `Ctrl-B` to the child

The full list lives in Keybindings.

Changing the prefix

If Ctrl-B collides with tmux, pick another:

constant host codex --prefix C-t
CONSTANT_PREFIX=C-t constant host codex

What a switch does

On a switch, Constant stops the current child, distills its active session, writes the target runtime's native session, and starts the target with its own resume command. No summary, no model calls. See How it works and What carries.

Pass-through, not a multiplexer

Constant hosts exactly one runtime at a time and forwards its output verbatim. It is not a terminal multiplexer or compositor, which is why the host stays small. There is no persistent status bar, by design.