They are officially Polaris 20 xtr even have their own chip codes labelled on the chip substrate, HIS also uses XTR in name for the SKU. It's 580 XTR
Polaris 20 XTX
(215-0910038)
Polaris 20 XTR
(215-0910066)
not all 7870s had XT in name either
GIGABYTE AORUS RX 580 XTR
HIS RX 580 XTR IceQ X2 Roaring Turbo
Labeling the die after binning is a common practice - look at Nvidia's Turing 'A' chips, that are still (correctly) sold under the same marketing names as their non-A siblings, just with an 'OC' or other indicator of higher performance tacked on to the name. That two OEMs share a semi-generic jumble of letters to designate a roughly matching but vague set of criteria is common as well.
As for the separate identifier, I guess that puts the lie to Gigabyte's claim of a bespoke binning process, as that's a clear sign of AMD doing the binning. I still wouldn't chalk up the new ID to anything more than binning, though - it still has identical specs to the base Polaris 20 XTX (boost clocks are determined per SKU, and AMD doesn't publish any specs for an XTR die), and again, the difference is no bigger than Nvidia's TUXXX-A chips.
