Via a colleague!

# Use Alt-arrow keys without prefix key to switch panes
bind -n M-Left select-pane -L
bind -n M-Right select-pane -R
bind -n M-Up select-pane -U
bind -n M-Down select-pane -D
# Shift arrow to switch windows
bind -n S-Left  previous-window
bind -n S-Right next-window
# No delay for escape key press
set -sg escape-time 0