The issue of respec costs, which refers to how difficult it is to change your character's build, is a sensitive topic for the Diablo community. The previous two games in the series had different philosophies: Diablo 2 made it extremely challenging, while Diablo 3 eliminated not only respec costs but also skill trees, allowing characters to be easily reshaped as desired.
For Diablo 4, lead class designer Adam Jackson discussed a compromise between the two in a recent roundtable call attended by Polygon. Initially, respeccing your character during the campaign up to level 50 is very inexpensive, almost free, but it becomes significantly more expensive during the game's endgame.
According to Jackson, the development team wants players to have the freedom to customize their characters and experiment with different builds, while also committing to a particular fantasy and character, creating a sense of weight and meaning to their choices. He admires how invested Diablo 2 players become in their highly specific builds and play styles, but he aims to eliminate the fear of making mistakes that might discourage early experimentation or hamper learning the game.