How do I open the alternate file in a new split window without typing its name?

Explanation

Press <C-w><C-^> (Ctrl+W followed by Ctrl+6) to open the alternate file in a horizontal split. The alternate file is the last file you visited — tracked by the # register — making this the fastest way to side-by-side compare or context-switch between two files.

How it works

• Vim keeps a special alternate file pointer (#) that always refers to the previous buffer you edited in the current window.
• <C-^> alone (Ctrl+6) toggles between the current and alternate file in the same window.
• <C-w><C-^> does the same but opens the alternate file in a new horizontal split, so both files are visible at once.
• The two windows are independent — you can scroll, edit, and close either one without affecting the other.

Example

1. You edit  config.yaml  (current file)
2. You then edit  app.go   (current file, config.yaml becomes alternate #)
3. Press <C-w><C-^>  →  app.go stays open, config.yaml opens in a new split above

Tips

• Use :echo expand('#') or :ls to see which file is the current alternate.
• Combine with <C-w>T to immediately move one of the panes into its own tab if you need more space.
• For a vertical split instead, use <C-w>v to open a vertical split, then <C-^> in the new window — there is no single-key vertical alternate-split command.
• The alternate file is per-window, so different splits can have different alternate files.