All of "Curb Your Enthusiasm" is indeed improvised, there is some sort of outline but my character wasn't major enough to get to see it. I didn't even know that my character was a lesbian which was kind of a major plot point but one that I didn't have scenes involving.

I never knew what the episodes were about until they aired, which was kind of awkward (laughs).

http://ew.com/tv/2017/06/15/mayim-bialik-career-beaches-blossom-big-bang-theory/