4TB Ironwolf has a new part number ST4000VN006 - the 2 platter drive and it will replace the ST4000VN008 part number soon.

Main difference is that ST4000VN006 has 2 disk platters, in contrast to 3 platters of ST4000VN008.  This means that the new part number is marginally ligher and energy efficient.  The new part number also has a better transfer rate (202 MB/s compared to 180 MB/s of earlier one)