Originally Posted by Doitsu
Actually, it's both.
I used KindleGen 2.8, which creates a master .mobi file that contains both a regular .mobi file and an .azw3 file. (KindleGen also attaches the source files, which can be extracted with 7Zip
But it's only the KF8 portion of the file which will work
. The older Mobi format doesn't support RTL languages.