The default number of moderators is always three.
Whether or not a site is graduated doesn't really affect whether that number increases. There's no set formula for calculating the number of moderators, if that's what you're asking, and it doesn't automatically increase after certain periods of time.
The answers over on How many pro tem moderators are chosen? Always three? are still completely relevant to graduated sites. There's also some information on this over at When do moderator elections take place? There are factors that go into the decision to appoint or elect more, such as the current workload (how much the moderators are having to handle), the activity of existing moderators, and how much we expect site-specific problems to arise. But the most important factor is whether the moderators think they even need more help, and if they do, they can request it. That's usually the primary trigger for adding more.