And now it's official, ATI did some selective rebranding of their Radeon HD 3000 generation to HD 4000 but this time they did it in their official Catalyst 9.1 driver.

The file called CH_75108.inf says it all. It shows 11 new cards branded as Radeon HD 4230, HD 4250, HD 4570, HD 4580, HD 4730 and finally HD 4750.

Take a quick look at this part of inf file

"ATI Radeon HD 4230" = ati2mtag_RV610, PCI\VEN_1002& DEV_95C5
"ATI Radeon HD 4230 " = ati2mtag_RV610, PCI\VEN_1002& DEV_95C5
"ATI Radeon HD 4250" = ati2mtag_RV610, PCI\VEN_1002& DEV_95C5
"ATI Radeon HD 4250 " = ati2mtag_RV610, PCI\VEN_1002& DEV_95C5
"ATI Radeon HD 4250 " = ati2mtag_RV610, PCI\VEN_1002& DEV_95C0
"ATI Radeon HD 4570 " = ati2mtag_RV630, PCI\VEN_1002& DEV_9598
"ATI Radeon HD 4580" = ati2mtag_RV630, PCI\VEN_1002& DEV_9598
"ATI Radeon HD 4730 " = ati2mtag_RV630, PCI\VEN_1002& DEV_9505
"ATI Radeon HD 4730 " = ati2mtag_RV630, PCI\VEN_1002& DEV_9505
"ATI Radeon HD 4750" = ati2mtag_RV630, PCI\VEN_1002& DEV_9505
"ATI Radeon HD 4750 " = ati2mtag_RV630, PCI\VEN_1002& DEV_9505

This clearly proves that the HD 42x0 generation is based on RV61x core that is behind HD 3400 brand, the new HD45x0 is based on RV63x core or HD 3600 generation and the new 47x0 brand is as well based on RV63x brand. These are not RV610 and RV630 cores, they are 55nm RV615 and RV635 brands and we got that by comparing the DEV IDs of 2400 series branded RV610 and the new one. At RV615 the DEV_95C5 is part of the name, while the 2400 series has DEV_94 in the name.

You can help yourself unpack the 9.1 driver and check it for yourself and it is rather interesting to see how tables have turned.