`man tmux`:
> bind-key [-nr] [-N note] [-T key-table] key command [arguments]
> Bind key key to command. Keys are bound in a key table. By default (without -T), the key is bound in the prefix key table. This table is used for keys pressed after the prefix key (for example, by default 'c' is bound to new-window in the prefix table, so 'C-b c' creates a new window). **The root table is used for keys pressed with- out the prefix key: binding 'c' to new-window in the root table (not recommended) means a plain 'c' will create a new window. -n is an alias for -T root.** Keys may also be bound in custom key tables and the switch-client -T command used to switch to them from a key binding. The -r flag indicates this key may repeat, see the repeat-time option. -N attaches a note to the key (shown with list-keys -N).
TL;DR: `bind-key -n C-t new-window`