An Engineering Journey Training Large Language Models at Scale on Alps: The Apertus Experience. - Jonathan Coles; Stefano Schuppli; Lukas Drescher; Fawzi Mohamed; Elia Palme; Henrique Mendonça; Miguel Gila; Mark Klein 002; Maxime Martinasso; Joost VandeVondele; Torsten Hoefler; Thomas C. Schulthess; et al. (CoRR, 2026)