This study examines sustainability governance in two Olympic mega-projects—Torino 2006 (ex-post) and Milano Cortina 2026 (ex-ante)—to understand how accountability, stakeholder engagement, transparency, and legacy are framed and evidenced. Using a qualitative approach, we conduct document analysis of nine primary sources (sustainability reports, strategy papers, environmental assessments, and institutional materials), triangulated across the pre-event, organizational, and event-start phases and coded on temporal sequencing, disclosure/transparency, stakeholder representation, and impact measurement. The comparison shows a move from Torino’s environment-focused, compliance model to Milano Cortina’s broader approach with GRI reporting and planned legacy evaluations. At the same time, persistent constraints emerge: the current absence of external assurance for Milano Cortina reports, the difficulty of operationalizing social and economic outcomes with evaluable counterfactuals, and the risk of selective interim indicators or limited inclusion of all categories of stakeholders. The study offers a preliminary assessment of disclosure practices and contributes to project management debates by positioning Milano Cortina 2026 within a changing accountability landscape. It underscores the need for post-event evaluations, transparent baselines and stable indicators, independent verification, and longitudinal designs capable of testing legacy claims beyond narrative compliance.