https://www.cnet.com/news/apple-updates-imac-line-with-more-cores-and-better-graphics-including-intel-core-i9-cpus/

Graphics go from Radeon Pro 555 and 560 GPUs to the newer Radeon Pro Vega 20. These changes only affect the $1,299 (£1,249, AU$1,999) and $1,499 base model 21.5-inch iMacs. The entry level $1,099 model, with a dual-core seventh-gen Intel Core i5, remains unchanged.

More interesting is what's happening to the 27-inch iMac. That model still starts at $1,799 (£1,749, AU$2,799) and comes with a standard 5K display, but the Intel CPUs start at eighth-gen six-core chips, and can go all the way up to the eight-core Intel Core i9, something usually only seen in high-end gaming systems or creative workstations. This could double performance speed in some applications, according to Apple.