If you're following -current, or if you upgrade your system with the next or a future snapshot, please note that the default setup for touchpads in X will change.
X will select ws(4) instead of synaptics(4) as default driver. In a configuration with ws, touchpad-specific input processing is done by wsmouse(4). Touchpad configuration parameters are made available in wsconsctl(4), see https://marc.info/?l=openbsd-misc&m=150153498920367&w=2 for some hints (the wsmouse man page is not up to date yet). Using synaptics(4) as input driver is still possible, it will require a custom xorg.conf file. If you already have such a file - which overrides the default -, please consider giving ws a try, and help us by reporting problems if it doesn't work for you.