Quanta cura is infallible.

[Kephapaulos]

The Theological Note of Integralism: The Teaching of Quanta cura is Definitive: Reply to Robert T. Miller by Dr. John P. Joy

[Geremia]

What about Pius IX's Syllabus of Errors? Cartechini says collections of condemned propositions aren't per se infallible; one must assess the authenticity of each condemned proposition in the context of the document from which it was drawn. Lamentabili, Pope St. Pius X's Syllabus, is a bit different (∵ it doesn't contain prop.s taken verbatim from other documents), but it doesn't define any new dogma.