According to a post by a community manager regarding the demo at E3, “As it was a pre-alpha build, the availability of health and focus consumables still has room for polish and the demo itself had the health and focus resources turned up above normal availability so that the press members could get a good feel for how things operated in a short time. Health and Focus DO NOT REGENERATE. They are based on consumables.”
Also regarding the enemy AI, it was revealed that the new stealth system is only slightly shadow-based. “Guards can look up. Their vision cone is actually really realistic and linked to their eyes. For example, if two guards are facing each other talking they cannot see what is behind the other because they are blocking each other’s views.”
There will also be two kinds of lock-picking: Normal and Focus Mode. The latter “makes it easier by bringing up the ‘inside the lock’ view. Without focus, the view is on the front of the lock, making things a little bit less straightforward”.
Thief is currently slated to release next year for Xbox One, PC and PS4.