Remember me functionality is now available for both normal logins (username/email + password) as well as for Single Sign On (GitHub, Bitbucket, GitLab).
The login is remembered for two weeks right now after a new sign in.
There’s no UI to opt out (we might add it in the future), but of course you can always use a private browser tab/window if you don’t want your login to be remembered.
Technical detail: a new sign in (on another device / in another browser) invalidates the previous browser’s remember token. So, in case you forgot to sign out somewhere, just sign in on another device to invalidate the previous device’s remember token. Note: this only works if you did close the session on the previous device (e.g. quit the browser), active sessions are not terminated, only the remember token.