CyanogenMod announced official CM13 nightly builds based on Android 6.0 Marshmallow for several devices, including the OnePlus One (bacon), LG G4 (h815) and Motorola Moto X 2014 (victara) last month, and started rolling it out soon after. Now it has released CM13 nightly builds for the Galaxy S3 (i9300), LG G3 S, G3 Beat , LG Optimus L70, LG Optimus L90 and more.
It already confirmed that it is planning to roll out CM13 based on Android 6.0 Marshmallow by the end of 2015. Oppo Find 7, Find 7s, Motorola Moto G, Moto G (2014), Moto G (2014) 4G and several devices got the CM13 nightly build few weeks back. CyanogenMod already said that more devices will be added to the roster over the next few weeks.
CM13 nightly builds for these devices are available for download from the official get.cm website. You need to wipe the phone completely if you have any unofficial, XDA or self made builds of the CM13 source code.