I don't know about the author, but I recently saw an article where the author of Claude code apparently spins up multiple instances at once (note that it could have just been a marketing ploy to get people to use more tokens)

https://www.xda-developers.com/set-up-claude-code-like-boris...

Just use Git worktrees and a lightweight VM environment (I like macOS native sandbox-exec) and you can spawn as many sessions as you want. I've run upwards of 30 at once on my M2 Pro with no noticeable resource impact.