At least big compared to the size that high resolution lithography is usually done over. They have made a very impressive sheet glass metalens surface etched onto one side using classic chip making technology.
10cm lens and a single piece of glass - pretty good resolution too
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I guess maximum size will be limited by standard fab line constraints.
It probably will have some applications in spot wavelength optics.
In some ways it is the ultimate quantum optics version of a Fresnel lens.