Announced today, the Snapdragon 821 offers a modest CPU frequency increase over the Snapdragon 820, with clock speeds of up to 2.4 GHz compared to 2.2 GHz with the Snapdragon 820. The new SoC is still implementing Qualcomm's custom quad-core "Kryo" design, which is made up of two pairs of dual-core CPU clusters.
"What isn’t in this announcement is that the power cluster will likely be above 2 GHz and GPU clocks look to be around 650 MHz but without knowing whether there are some changes other than clock relative to Adreno 530 we can’t really estimate the performance of this part."
Specifics on the Adreno GPU were not mentioned in the official announcement. The 650 MHz GPU clock reported by Anandtech would offer a modest improvement over the SD820's 624 MHz Adreno 530 GPU. Additionally, the "power cluster" will reportedly move from 1.6 GHz with the SD820 to 2.0 GHz with the SD821.
No telling when this updated SoC will find its way into consumer devices, with the Snapdragon 820 currently available in the Samsung Galaxy S7/S7 Edge, LG G5, OnePlus 3, and a few others.