Thanks to the folks at CyanogenMod, they have released CyanogenMod 13 for the Galaxy S5 which will essentially bring Android 6.0 Marshmallow to the handset. However we should point out that this version of CM13 is still a nightly build meaning that if you wanted to use it as your daily driver, it’s probably not the best idea.
It might not also be the most stable build yet and there are probably a few bugs and features that don’t work 100% yet, but at the same time if you’d like to check it out you can go ahead and download it via the CyanogenMod website. We would also like to point out that this build will only work on GSM models of the Galaxy S5.
This means that users on Sprint or Verizon are out of luck, and interestingly enough according to Android Police, it seems that this won’t play nicely with the AT&T variant either. So either you’ve got to own the T-Mobile version of the handset, or an international GSM variant.