The The Hidden Ones Add-on for Assassin's Creed Origins has 8 achievements.
Free 20 Rebels (The Hidden Ones)
Perform a leap of faith from Arsinoe's sundial obelisk between 10 am and noon (The Hidden Ones)
Perform 3 Assassinations from a zipline (The Hidden Ones)
Kill an enemy with a headshot while they are being harassed by Senu (The Hidden Ones)
Complete the Walls-of-the-Ruler citadel (The Hidden Ones)
Assasinate Tacito, Ptahmose and Ampelius (The Hidden Ones)
Complete Side DLC Quests "Rise of Shaqilat" and "Shadows of the Scarab" (The Hidden Ones)
Complete Main DLC Quest "The Greater Good" (The Hidden Ones)