Notebook Check has spotted that the latest 10th-generation parts found in the Apple laptop are unlisted on Intel’s Ark of Ice Lake parts despite Apple's recent product launch. It would seem then, at least for the time being, Apple has exclusive access to this silicon from Intel although it has previously revealed these parts will be hitting the market about now.
The current top of the line Ice Lake part listed on Intel’s website is a Core i7-1065G7 quad-core 15 W part (configurable up to 25 W) chip with a base frequency of just 1.3 GHz with boost to 3.9 GHz. Even the Core i5-1038G7 (28 W) part available for the new 13-inch MacBook Pro has a base clock of 2.0 GHz and can boost to 3.8 GHz. The new Core i7-1068G7 (28 W) part has a base clock of 2.3 GHz and can boost to 4.1 GHz making both chips the highest performing Ice Lake parts currently found in any notebook by some margin.
Intel has had problems with its 10nm parts and mass quantities of the 10th-generation parts available to other OEMs are capped at a base clock speed of just 1.3 GHz. This suggests that Intel may not yet have sufficient yields of the higher-performing chips to offer more widely.