The AKC standard states "not to exceed 7 pounds". While there is no low end to that statement, a 0.1 lb dog would still fall under that guideline, while I hope it never comes to that!
https://www.akc.org/breeds/yorkshire...d_standard.cfm
There is no official classification of teacup in yorkies. People get confused bc dogs such as poodles have "standard", "mini", and "toy". Not yorkies. They all all in the "toy" group.
Take note in the AKC standard to the deviation in coloring as well. A lot of breeders will charge more for an off color, which is considered a fault, and say it is rare. Do not be duped!