Both are quad-core processors with no Hyper-Threading. They also lack the Boost functionality but they come with pretty high base clockspeeds. The Core i3-8350K is a version with an unlocked multiplier and it also has 8MB L3 cache, versus 6MB on the 8100 model.
The Core i3-8350K is a particularly interesting SKU. This 4-core/4-thread chip features an unlocked base-clock multiplier, and 8 MB of L3 cache, as opposed to 6 MB on the i3-8100. Just as Intel previously differentiated its Core i3-x1xx SKUs from i3-x3xx SKUs by giving the latter 33.33% more L3 cache, the trend is continuing with the 8th generation, except that both the core-count and L3 cache amount has doubled over the 7th generation.Below is a quick look at the specs of the six Coffee Lake-S models that are expected on October 5, 2017: