Full details to follow soon (in a separate article) but meanwhile here are the headlines:
Unprecedented Highest Resolution and Widest Dynamic Range for α - Alpha System, Combined with High-speed Performance and a Lightweight, Compact Body
World’s first 35mm full-frame 61.0 MP back-illuminated Exmor R™ CMOS image sensor with latest-generation BIONZ X™ image processor
15-stop dynamic range at low sensitivities, resulting in smooth, natural gradations ranging from deep shadows to highlights
High-speed continuous shooting at up to 10 fps with full AF / AE tracking for approximately seven seconds in full-frame mode with an increased buffer memory, and approximately three times as long in APS-C mode
567 focal-plane phase-detection AF points covering 74% of image area and 425 contrast AF points
Debut of Real-time Eye AF for movie recording and advanced Real-time Tracking plus Real-time Eye AF for still image recording
Features an APS-C crop mode delivering stunning high resolution images of 26.2MP
5.76 million dot UXGA (Ultra-XGA) OLED Tru-Finder™ electronic viewfinder with outstanding detail, brightness and contrast
Upgraded connectivity and operability including high-speed Wi-Fi support, wireless PC remote connectivity, FTP wireless transfer, faster data transfer via USB and more
Professional 4K movie recording functionality including full pixel readout with no pixel binning in Super 35mm mode[, S-Log3, HDR workflow support
Multi Interface Shoe™ with digital audio interface delivers the high-quality sound recording with Sony’s new microphone and XLR microphone adaptor
Additional enhancements to the body design include an improved grip and button layout for improved control with compact, lightweight body
This camera genuinely looks like it's a significant improvement. Neal Manowitz, deputy president of Imaging Product and Solutions Americas at Sony Electronics says it has "medium format-level image quality".
According to Sony's press release the new camera has a newly developed 35mm full frame, back-illuminated CMOS sensor with a resolution of 61 megapixels. It's evident that image processing plays a large part in creating the final images from the camera: "The new sensor's back-illuminated structure and effective noise reduction techniques combine to deliver extremely low-noise and high-sensitivity performance, ensuring the absolute maximum image quality."