Product-Service Systems, like all complex systems, are vulnerable to unpredictable environmental changes that can seriously undermine their ability to continuously deliver value to customers. The long-term consequences of volatile markets, unanticipated technologies, and unpredictable changes in society must be captured, modeled and communicated to decision makers since the earliest stages of the design, so to identify sustainable PSS solutions able to deliver value for years or decades to come. The paper analyses the problem of PSS changeability from the perspective of established medium-large product manufacturers facing the transition toward result-oriented PSS offers. Building on established literature in the systems engineering field, the paper proposes the definition of the changeability criteria, also named ‘ilities’, that are relevant to consider for PSS engineers in the early stages of design. Furthermore, the paper describes a systematic framework for assessing ilities in early PSS design, elaborating on technological enablers for ilities modeling.