When viewing a file on GitHub, pressing the y key will update the URL to a permalink to the current revision you’re viewing.

The default the version of a file that you see is the at the current head of a branch:

https://github.com/j4ckofalltrades/j4ckofalltrades/blob/main/README.md

By using this keyboard shortcut you get a permalink to the specific version of the file which contains the SHA commit hash in the URL:

https://github.com/j4ckofalltrades/j4ckofalltrades/blob/6afb8559a813123da1cd85142410169c825bee40/README.md


Tip
Pressing ? on any page in GitHub shows all the available keyboard shortcuts.