bun.sh/docs/cli/bun-completions.md

This command installs completions for zsh and/or fish. It runs automatically on every bun upgrade and on install. It reads from $SHELL to determine which shell to install for. It tries several common shell completion directories for your shell and OS.

If you want to copy the completions manually, run bun completions > path-to-file. If you know the completions directory to install them to, run bun completions /path/to/directory.