Unfortunately, if you've been reading the rumors, they were true: it's going to be a paid option, and will cost $100. Since this took so long to come out, the assumption is that Panasonic spent a lot of resources on making it much more than just a flat picture profile — which is why this isn't free like other upgrades we've gotten from Panasonic. Essentially if you want the log profile on your camera (which improves dynamic range from 10 to 12 stops), you'll be buying a license that is tied to your camera's serial, so you wouldn't be able to transfer it to other cameras temporarily. Firmware version 2.3 firmware will still be a free update, but the option to use V-Log won't be unlocked until you buy the key from Panasonic (this will be mailed to you, it's not available for download). 

Here is Panasonic on the new V-Log:

In response to the demand from the film production market, log video recording (V-Log L) is now available for the LUMIX GH4, and offers exceptional flexibility as well as wider dynamic range for color grading in post-production process. V-Log / V-Log L were developed to feature similar characteristics to Cineon, which is a characteristic curve for film digitalization. Taking full advantage of Four Thirds sensor, V-Log L boasts a log characteristic with 12 stops. Both V-Log and V-Log L have the same characteristic curve, and LUT (Look Up Table) can be utilized.

Eduardo Angel has been using V-Log for a while now, and shows us what it can do in these videos:

You can also see a comparison of V-Log to S-Log from Nick Driftwood. Here is the Sony a7S on the left wtih SLog2 and the GH4 with V-Log on the right:

Features of the V-Log firmware upgrade:

  • LUMIX GH4 function enhancement for film production/professional videographers
  • Increases dynamic range from 10 stops to 12 stops 
  • Makes color grading easier with improved compatibility between LUMIX GH4 and Panasonic Varicam
  • V-Log / V-Log L were developed to feature similar characteristic to Cineon
  • One Key Per Camera
  • Sales Are Regional Outside the USA
  • Not Sold As a Download
  • Key is Locked to GH4 Serial Number
  • Availability: Mid September
  • Price: $100

And here's the install process for V-Log:

The company has also announced a brand new version of the GH4, called the GH4R, which includes this V-Log internally, and also removes the recording time limit. This camera will not be sold in the US, however, it will be a European-only model (at least for now):

You won't have long to find out for yourself how this profile compares with other profiles in the camera (and with other cameras), as it is set to be released sometime in the middle of September. You can pre-order now from both B&H and from Panasonic

Source: Panasonic