Quantum distillation works even when you don't know your input state

Purifying quantum resources like entanglement normally requires knowing exactly what noisy state you're working with. This work proves that isn't necessary: universal protocols exist that hit optimal distillation rates regardless of the input, under resource non-generating operations. The key technical engine is a generalization of the quantum Stein's lemma to a composite hypothesis-testing setting, where the null hypothesis is an unknown i.i.d. state rather than a fixed one. For entanglement specifically, the optimal rates are still governed by the regularised relative entropy of entanglement, confirming that universality costs nothing in performance.