In Path of Exile, there are currently 10 acts that make up the main storyline campaign. However, the way you experience these acts may depend on when you began playing:
Pre-3.15 Expansion: Prior to the release of the 3.15 "Echoes of the Atlas" expansion in February 2020, the campaign structure was different. It involved:
3.15 Update and Beyond: With the 3.15 update, the campaign was streamlined and restructured:
So, in essence, regardless of when you started playing, there are still 10 acts of story content in Path of Exile. However, the way you experience them and the subsequent end game will differ depending on when you began your journey.
I hope this clarifies the act structure in Path of Exile! Feel free to ask if you have any further questions about the game’s campaign or progression.