Bethesda's https://bethesda.net/#en/events/game/fallout-4s-character-system/2015/09/24/31: "Levelling is experience point (XP) based like Fallout 3, not skill-based like Skyrim. But levelling speed is closer to Skyrim, and not as slow as Fallout 3. This means you’ll be getting more opportunities, especially early on, to level up and select a Perk. Additionally, whereas Fallout 3 had an initial level cap of 20, Fallout 4 has no level cap, and we’ve balanced the game to keep the content and challenge going for higher levels."
Skyrim had a soft cap around level 40 or 50, or at least that was the point where leveling became a slog and all of the encounters stopped scaling. Fallout 4, we'll be able to keep leveling as long as we keep playing, absolutely; but it won't be fast enough that we max out the entire chart without a long grind.