You can now see the full A7rIV versus A7rIII specs comparison table on this special BHphoto page. Something unexpected can be noticed: The new A7rIV has a slightly smaller sensor!

Sony A7rIV and new accessories:
Sony A7rIV in USA/CA at BHphoto, Adorama, FocusCamera, Amazon, BuyDig, Henrys.
Sony A7rIV in EU at Calumet DE, ParkUK, WexUK, Calumet NL.
Sony A7rIV in Asia at Sony Japan. Sony Australia.
Sony VG-C4EM grip in USA at BHphoto, Adorama, Amazon, FocusCamera, BuyDig, ParkUK, WexUK.
ECM-B1M Digital Audio Shotgun Microphone at BHphoto, Adorama, BuyDig, Park UK.
XLR-K3M Mic at BHphoto, Adorama, BuyDig, Park UK.

Sony A7rIV and new accessories:
Sony A7rIV in USA/CA at BHphoto, Adorama, FocusCamera, Amazon, BuyDig, Henrys.
Sony A7rIV in EU at Calumet DE, ParkUK, WexUK, Calumet NL.
Sony A7rIV in Asia at Sony Japan. Sony Australia.
Sony VG-C4EM grip in USA at BHphoto, Adorama, Amazon, FocusCamera, BuyDig, ParkUK, WexUK.
ECM-B1M Digital Audio Shotgun Microphone at BHphoto, Adorama, BuyDig, Park UK.
XLR-K3M Mic at BHphoto, Adorama, BuyDig, Park UK.

And last but not least sum fun with Camera Conspiracies:

Tony Northrup posted the first comparison between the Sony a7R III vs a7R IV JPG images. The difference is bigger than I had expected:

Sony A7rIV and new accessories:
Sony A7rIV in USA/CA at BHphoto, Adorama, FocusCamera, Amazon, Henrys.
Sony A7rIV in EU at Calumet DE, ParkUK, WexUK, Calumet NL.
Sony A7rIV in Asia at Sony Japan. Sony Australia.
Sony VG-C4EM grip in USA at BHphoto, Adorama, Amazon, FocusCamera, ParkUK, WexUK.
ECM-B1M Digital Audio Shotgun Microphone at BHphoto, Park UK.
XLR-K3M Mic at BHphoto, Park UK.

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  Sony A7rIV (left) vs Sony A7rIII (right)

We got these new Hands-on images by DC.watch and CameraBeta. They do include the first real world images of the A7rIV on the battery grip (click to enlarge):

More tests:
Sony a7R IV: What you need to know (Dpreview).
Sony a7R IV’s real-time Eye AF during video recording (Dpreview).
Sony A7R III vs A7R IV – The 10 main differences (MirrorlessComparison).
Sony A7R IV: primeras impresiones (Photolari).

Sony A7rIV and new accessories:
Sony A7rIV in USA/CA at BHphoto, Adorama, FocusCamera, Amazon, Henrys.
Sony A7rIV in EU at Calumet DE, ParkUK, WexUK, Calumet NL.
Sony A7rIV in Asia at Sony Japan. Sony Australia.
Sony VG-C4EM grip in USA at BHphoto, Adorama, Amazon, FocusCamera, ParkUK, WexUK.
ECM-B1M Digital Audio Shotgun Microphone at BHphoto, Park UK.
XLR-K3M Mic at BHphoto, Park UK.

From generation to generation the A7r camera size keeps growing. This is the accurate size comparison between the “old” A7rIII and the new A7rIV via CameraSize.

Sony A7rIV and new accessories:
Sony A7rIV in USA/CA at BHphoto, Adorama, FocusCamera, Amazon, Henrys.
Sony A7rIV in EU at Calumet DE, ParkUK, WexUK, Calumet NL.
Sony A7rIV in Asia at Sony Japan. Sony Australia.
Sony VG-C4EM grip in USA at BHphoto, Adorama, Amazon, FocusCamera, ParkUK, WexUK.
ECM-B1M Digital Audio Shotgun Microphone at BHphoto, Park UK.
XLR-K3M Mic at BHphoto, Park UK.

And a real world size comparison by Manny Ortiz:

You can find new image samples on those pages:

45mm f/2.8 image samples at Fengniao.
35mm f/1.2 image samples at Fengniao.
14-24mm image samples at Fengniao (scroll down).

New hands-on images at Dpreview.

Sigma FE lenses:
Sigma 35mm f/1.2 FE at Adorama, BHphoto, FocusCamera, Henrys. In EU at ParkUK, WexUK.
Sigma 14-24mm f/2.8 FE at Adorama, BHphoto, FocusCamera, Henrys. In EU at ParkUK, WexUK.
Sigma 45mm f/2.8 FE at Adorama, BHphoto, FocusCamera, Henrys. In EU at ParkUK, WexUK.

USA/CA Preorders:
Sony 200-600mm FE at Amazon, BHphoto, FocusCamera, BuyDig, Adorama and Henyrs.
Sony 600mm FE GM at Amazon, BHphoto, FocusCamera, BuyDig, Adorama and Henyrs.
EU Preorders:
Sony 200-600mm FE at Amazon DE. Calumet DE. Amazon UK. WexUK. ParkCameras. Amazon FR. Amazon IT. Amazon ES.
Sony 600mm FE GM at Calumet DE.WexUK. ParkCameras.
Asia Preorders:
Sony 200-600mm FE at Sony Japan. Sony Australia.
Sony 600mm FE GM at Sony Japan. Sony Australia.

Sony FE 600mm f/4 GM OSS test by Ole J Liodden:

My overall impression of this new telephoto lens is that it is extremely well made, fast, reliable and light-weighted. It is difficult to find anything to improve, maybe except the pricing. Hopefully I will have another chance soon to use the lens on an expedition to test it in different situations.