Instant Sneak brings back the old instant sneak, removing the camera animation when crouching and keeping all other camera behavior intact.
Inspired by Sneak Tweak, Instant Sneak features a fully configurable camera that allows you to change the crouching camera height, enable/disable the animation and modify the animation speed. These settings can be changed within the config file, in your Minecraft instance folder at /config/instant-sneakconfig.properties.
By default, the camera height is set to 75% inbetween new and old height, to minimize clipping while going under slabs.