The precise wording matters
The nine major U.S. food allergens are milk, egg, fish, crustacean shellfish, tree nuts, peanuts, wheat, soy and sesame. Yeast is not on that list. That does not mean yeast allergy is impossible, and it does not make every product “allergen-free.”
Vegan, dairy, soy and gluten questions
Yeast is a fungus and can be compatible with vegan diets when no animal-derived components are used. Pure yeast protein does not inherently contain milk or soy, but formulations and shared equipment differ. Do not assume every yeast protein is gluten-free: people who medically require a gluten-free diet should choose a finished product that meets applicable labeling requirements.