kmk_firmware/docs/oneshot.md

OneShot Keycodes

OneShot keys or sticky keys enable you to have keys that keep staying pressed for a certain time or until another key is pressed and released. If the timeout expires or other keys are pressed, and the sticky key wasn't released, it is handled as a regular key hold.

Enable OneShot Keys

from kmk.modules.oneshot import OneShot
oneshot = OneShot()
# optional: set a custom tap timeout in ms (default: 1000ms)
# oneshot.tap_time = 1500
keyboard.modules.append(modtap)

Keycodes

Keycode	Aliases	Description
KC.OS(KC.ANY)	KC.ONESHOT	make a sticky version of KC.ANY

KC.ONESHOT accepts any valid key code as argument, including modifiers and KMK internal keys like momentary layer shifts.

Custom OneShot Behavior

The full OneShot signature is as follows:

KC.OS(
    KC.TAP, # the sticky keycode
    tap_time=None # length of the tap timeout in milliseconds
    )