6.0.1_r20 for the Nexus 5 and Nexus 9, and 6.0.1_r24 for the Nexus 5X. You can see the versions of the downloads page (it uses AOSP_TAG.COPPERHEADOS_TIMESTAMP)

6.0.1_r20 for the Nexus 5 and Nexus 9, and 6.0.1_r24 for the Nexus 5X. You can see the versions of the downloads page (it uses AOSP_TAG.COPPERHEADOS_TIMESTAMP) It's the same as stock. It will move to 7.0 shortly after it's released.