The VC is 4.1mm. Making the JLC Jubile Ultrathin at "4.05mm" looks really like a trick to pretend to be the thinnest.
Let's see what the watch looks like, specially the edge to see if it really is 'knife edge' as intended.
As for the record claimed by the manufacture to have created the thinnest handwound mechanical wristwatch and having established a new breakthrough record, this is simply not true (by far).
However, the watch does look quite good from what we can see in the first sneak pictures regardless of the 'record' status.
Pierre-Mathys-designed Jean Lassale calibre 1200 was 1.2 mm thick (hence its name ! )
It was later fabricated by Lemania under reference 1210 and used by Piaget (calibre 20P) and then by Vacheron Constantin (calibre 1160)
Jaeger LeCoultre calibre 849 is 1.85mm, so 0.65mm or 54% thicker than the Lassale/Lemania/Piaget/Vacheron movement + the Jubile Ultrathin watch has a domed front crystal that counts in / adds to the total thickness
Some quote that there has been a series of 12 Lassale watches at 2mm total thickness, but source is unclear, and I don't believe this is possible (I have seen Lassale watches with double flat crystals (front+back) which are 0.37mm thick each, and you inevitably need a little space for the dial and some for the 2 hands so 2mm is simply too short). However, I have seen several times the most common versions of Lassale which are 3.7mm total height