They linked the kilogram to the gravitational force.
It’s part of an effort to clarify how we define things. We’re now trying to link our recorded units to the basic forces they are related to. So now, the kilogram is defined by the gravitational force, the meter by how fast light travels, etc etc
The kilogram is defined as the mass equivalent of a photon of a specific energy via the Planck constant h thus linking the speed of light and the frequency of the hyperfine level of caesium-133. The relative uncertainty of the measured value of the gravitational constant G is 10^-5 which would lead to a definition of the kilogram that has a worse relative uncertainty than using the former definition defined via an international prototype. The Wikipedka article is more detailed than this short summary.
