Earlier quoted context omitted.
Safari lets extensions precompile a list of patterns to block and then it does the actual blocking. The extension never sees your browsing history or network requests.
Sounds a lot like what Chrome is bringing in.
Originally, Google wanted to max at 30k items, but after the outry, they increased it to 150k.
For comparison, my uBlock has currently 101k of net filters and 49k cosmetic filters.