Here is short info about 2020 sneak rework. Disclaimer: as of current state the rework is heavily WIP and is probably partially bugged and 100% not working as final image is intended to, so report your feedback but consider the fact this is mostly a stub as of now (especially in terms of balance.
There are 3 new stealthboys: Recon Stealth Boy, Infiltrator Stealth Boy and Ambush Stealth Boy.
They work as follows:
1) Recon Stealth Boy provides you permanent concealment sneak (that is more of a reduction of your sighting range than a true invisibility) and is having an active temporary boost - Warmode. Warmode halves your detection range for a limited amount of time (10 seconds), is halving your bonus sight (all sight above base 20 hexes) and has 5 second cooldown after it expires. The recon stealthboy is a most versatile one, but it comes with disadantage of having a severe weight limit: anything above 6-7 kg load will negate most of your stealth.
2) Infiltrator Stealth Boy is a Warmode-only stealthboy, meaning that at activation it will put you into 10 seconds temporary sneak, that has a 5 second cooldown on expiry. The weight penalty on stealthboy allowing to carry up to 15-18 kg of gear without a significant penalty.
3) Ambush Stealth Boy is a concealment-only stealthboy, meaning it mostly acts as a reduction to sighting range and is not intended to hide you at close range. This stealthboy is active only when you are stationary and stealth will break on any movement. The weight penalty is similar to Infiltrator, so way more forgiving than a Recon Stealth Boy one.
Stealthboy effects general overview:
The new mechanics is that instead of fixed Sneak Value (current practically used skill for sneaking, displayed in top left corner) there is a dynamic one. Each stealthboy has a maximum efficiency of 100, 10 of which is regenerated each second. The stealthboy efficiency is reduced when character is moving or performing attacks, and reduction in stealthboy proportionally affects Sneak Value. Once Sneak Value reaches 0 - character desneaks.
Instead of being instantly desneaked on attack character now takes a stealthboy efficiency reduction, equal to weapon_weight_in_kg * 20 (half of that for Silent Attack weapons), and if the Sneak Value reaches 0 as a result - only then characer desneaks.
Bonus for being next to wall is massively buffed and integrated into default sneak behaviour: you will get 50% more Sneak Value from beign within 3 hexes next to wall, and 100% more sneak value if you have Ghost character perk.
Shadow character perk is gone as it wont have any effect in new system.
Warmode hotkeys are gone and Stealth Boy will transition into being a Util slot item so you can activate Warmode via Util slot hotkey.