Yes. All gameplay content in Skull and Bones is available for free.
There’s a slight clarification needed about free content in Skull and Bones.
The base game itself requires purchase.
However, all post-launch content, including Seasons (like the current "Raging Tides"), is completely free. This means you get new story content, world events, challenges, and even some cosmetic rewards without paying extra.
Ubisoft has committed to a year of free content updates for Skull and Bones, so you can expect more to come in the future.