Sprint's variant of the LG G4 is now receiving the Marshmallow. The carrier's website lists the official rollout commencing from December 17, and notes that the update will be available in phases.

The Marshmallow update will bump the version number to LS991ZV9, and introduce Sprint's global roaming feature. If you're using an LG G4 from Sprint, now would be a good time to head into your device's settings to check if the update is available for your phone.

Source: Sprint

Thanks Robert Eldridge!