I'm not at all an expert on generics, but the company suing to remove exclusivity has almost certainly done some groundwork needed to produce the generic drug. They likely need to figure out how to produce the drug as well as some business stuff like market determination, so a second generic manufacturer is probably a bit behind.
for significant small molecule drugs, there is commonly a cohort of generic firms ready at expiry. There is usually little barrier to entry beyond the patent or regulatory exclusivities. Prices are typically crushed after the 6 months.
Biologics (antibodies/ vaccines) are a different story because of the complexity of their manufacturing and characterization.
