Set tmux pane title to short hostname on ssh connections for Fish

set-tmux-title

# Copy that into your ~/.config/fish/config.fish

function ssh
  set ps_res (ps -p (ps -p %self -o ppid= | xargs) -o comm=)
  if [ "$ps_res" = "tmux" ]
    tmux rename-window (echo $argv | cut -d . -f 1)
    command ssh "$argv"
    tmux set-window-option automatic-rename "on" 1>/dev/null
  else
    command ssh "$argv"
  end
end

I added some of the recs from the comments and also made this support ssh arguments such as -X or -L.

function ssh
  ### automatically renames tmux pane with hostname when using SSH
  
  # check if tmux is running
  if test -n "$TMUX"
    # assume first arg not starting with '-' is hostname
    set hname -- $argv
    for a in (string split -- ' ' $argv)
      if not string match -- '-*' $a
        set hname -- $a
        break
      end
    end
    tmux rename-window $hname
    echo -- $argv
    command ssh $argv
    tmux set -w automatic-rename "on"
  # if not running tmux, just use ssh
  else
    command ssh $argv
  end
end

Note that this version assumes that the first arg not starting with a dash is the hostname, so if will be wrong if you do something like ssh -L 5901:192.168.1.42:5901 hostname. Instead, you have to do ssh hostname -L 5901.192.168.1.42:5901

@darren-muon awesome, thank you so much!