Google seems to have presumably started the rollout of Android 6.0.1 Marshmallow for its Android One range of smartphones. The update seems to be in its early stages of rollout with only a handful of people receiving it. Android 6.0.1 does not really bring anything new to the table. It is likely that the update only contains some bug fixes and stability improvements.
From the screenshots posted online, Google seems to have merged its December security patch with the Android 6.0.1 update. For now, the update only seems to be available for the One Cherry Mobile G1 Android One handset that is available in the Philippines.