Why the second pane opens instantly

Open a fresh terminal and start a coding agent. Before you can type, it has to load its runtime, check its sign-in, read its configuration and usually index the workspace. That takes a few seconds — sometimes much longer in a large repository.

A few seconds is nothing once. It is a lot when you open panes all day, and it breaks the flow of “I want another agent on this, now.” So PaneScale starts them before you ask.

#The idea

For every free cell of the grid in the active workspace — plus one spare, so even a full grid can grow — PaneScale keeps a session that has already started. When you open a pane, the waiting session is simply handed over. The pane appears with the agent ready for input, in milliseconds.

The waiting sessions live in the app’s backend, without a terminal on screen. Their output is buffered, and the startup queries a CLI sends to its terminal are answered right there, so the agent never hangs waiting for a reply. When a pane takes a session over, the buffered output is replayed and the session continues as if it had always been visible.

#Not eating your machine

Naively, “a session behind every cell” on a 16-pane grid means sixteen agents running for nothing. That would be a terrible trade. So pre-warming is careful:

• Low priority. Waiting sessions — and the processes they start, such as MCP servers — run below normal CPU priority. Your real work always comes first.
• A memory budget. PaneScale estimates what each waiting session costs (about 450 MB for Claude Code with its MCP servers) and always leaves at least 4 GB of memory free. If the budget runs out, fewer sessions wait.
• Throttled. At most four sessions start at the same time, and after a failed start PaneScale pauses for a minute instead of trying again and again.
• Bounded per agent. Up to thirty for Claude Code, three for Codex and two plain shells.
• Kept fresh. A session that has waited for 30 minutes is replaced by a new one, so a pane never starts with stale state.

When you take a session, it is switched back to normal priority immediately.

#When the pool is empty

If you open panes faster than sessions can start, the pane starts right away and PaneScale’s start queue staggers the launches, so a burst of new panes doesn’t make every one of them slow. You can type immediately — your input waits for the agent and is sent as soon as it is ready.

#Start options are part of the key

If you start Claude Code with a different effort level, a different account or without permission prompts, a session warmed with the default options wouldn’t be the same thing. So the options are part of the pool key: a pane only receives a pre-warmed session that was started exactly the way the pane asks for.