Sea 3 was added to Blox Fruits in Update 15 , which was released in September 2021.

Quick Scoop

The Third Sea is described in later guides as part of the game’s third-sea content, but the clearest release note points to Update 15 as the update that introduced it.

What that means

  • Update: 15.
  • Release window: September 2021.
  • Feature added: Third Sea / Sea 3.

TL;DR

Sea 3 was added in September 2021 during Blox Fruits Update 15.