Nutanix AHV works with Thin. In ESX you can use both. 

More info here: https://www.joshodgers.com/2017/07/27/its-2017-lets-review-thick-vs-thin-provisioning/

https://portal.nutanix.com/page/documents/solutions/details?targetId=TN-2032-Data-Efficiency:thin-provisioning.html#:~:text=Thin%20provisioning%20on%20Nutanix%20outperforms,Fault%20Tolerance%2C%20require%20thick%20provisioning.
 

For AHV disk will be thin only. for ESXi you can chose thick or thin 

This was my assumption as well...However, why does API respond with the following:

            {
                "disk_address" : 
                {
                    "device_bus" : "scsi",
                    "device_index" : 1,
                    "disk_label" : "scsi.1",
                    "ndfs_filepath" : "/storagecontainer/.acropolis/vmdisk/7c22b170-1400-4dc6-8434-79b40884089e",
                    "vmdisk_uuid" : "7c22b170-1400-4dc6-8434-79b40884089e"
                },
                "flash_mode_enabled" : false,
                "is_cdrom" : false,
                "is_empty" : false,
                "is_scsi_passthrough" : true,
                "is_thin_provisioned" : false,
                "shared" : false,
                "size" : 6442450944000,
                "storage_container_uuid" : "f396603a-ce0f-4d33-9a6b-4fe2695f698c"
            }

I am trying to reproduce the above output but alas, mine consistently shows ‘true’ for is_thin_provisioned. 

Nutanix AHV uses thin only, ESXi uses thin and thick