Spirit Walker can tame one Unique Beast at a time in PoE2, according to the current build notes and guides I found. The best-known summary also says the ascendancy can tame beast bosses, but the cap for a Unique Tamed Beast is up to one summoned.

Quick read

  • Unique tamed beasts: 1 active at a time.
  • Boss beasts: Spirit Walker can tame certain beast bosses during progression, but that does not change the unique-beast cap.
  • Other spirit summons: Spirit Walker’s spirit branches can add extra effects or companions, but they are separate from the Unique Tamed Beast limit.

What this means

If you were asking how many animals a Spirit Walker can tame overall, the answer depends on the category. For the special Unique Beast slot , it’s one. For the broader “which beast bosses can be tamed” question, the number varies by act and content, with guides showing multiple tameable bosses across Acts 1–3.

TL;DR

Spirit Walker’s Unique Beast tame limit is 1.