AMC’s horror series “The Walking Dead” reaches a significant television milestone on Sunday: Its Season 8 premiere is also its 100th episode, a traditional benchmark of enduring success and the ability to unlock even greater profits through syndication sales.

But wait. It’s only been 100 episodes? Doesn’t it feel as if the show has been sneaking through the woods and motoring down the abandoned highways of the zombie-plagued rural South for a lot longer than that?

And the road stretches endlessly into the future. While other successful shows of the same vintage are gracefully pulling down the curtain — “The Americans” and “Game of Thrones” have both announced that their next seasons will be their last — the producers of “The Walking Dead,” with plenty of comic books remaining to adapt, talk cheerily of another 100 episodes.

[ What to remember before watching Season 8 of “The Walking Dead.” ]

It’s silly to argue with success, when a show has dominated the ratings for most of its run (and when it and its offshoots support hundreds, probably thousands of workers). But Sunday’s premiere, the only new episode available in advance, finds “The Walking Dead” circling in the same storytelling stasis that has marked its last few seasons. It moves along in a lurching shuffle it seems to have picked up from the walkers, its decomposing zombie hordes.