In addition to the price increase ($3,498 to $4,498), here is the list of improvements in the new Sony A9 II mirrorless camera (pre-orders now open at: Adorama, B&H and Amazon):
Upgraded BIONZ X image processor - said to give improved AF/AR detection, image processing, face detection and accuracy.
Upgraded dust and moisture resistant design - with stronger sealing provided at all body seams
Latest image-processing algorithm - to reduce noise in the medium-to-high sensitivity range, whilst also improving resolution and image quality
Improved Image Stabilization - 5.5stops
Improved grip, with improved comfort, also compatible with Sony VG-C4EM vertical grip
Improved button design and feel, with a bigger AF-ON button, refined joystick, exposure comp dial lock button, with a redesigned shape and position for rear dial
Redesigned shutter mechanism to suppress movement that can cause image blur (still rated for 500,000 shutter cycles)
USB Type-C connection
Dual media slots now both support UHS-II
Digital audio interface has been added to the camera's multi-interface show (MI shoe) to support ECM-B1M shotgun mic, or XLR-K3M.
faster Ethernet connection and 5ghz Wifi modem.