Typekit developed dynamic kits to accommodate East Asian web font serving. The large size of East Asian fonts — well over 10,000 glyphs in most cases — otherwise makes it unrealistic to load these fonts on a website without significantly impacting the load time.
When you add an East Asian font family to your kit, it automatically becomes a dynamic kit and the Dynamic Subsetting character set option is selected.
The dynamic kit looks for any change to the DOM — such as a news feed or a comments section — and then requests any new characters that need to be added to the subset. We call this dynamic augmentation, and it’ll happen automatically for any of the font families in your kit that use the dynamic subsetting option.
This way, instead of downloading an entirely new font, we can now simply request the additional glyphs and perform the update right in your browser.