Unlike traditional e-commerce funnels, Steam does not pass source data cleanly through the user journey. Players move between browsers, the Steam client, and the game itself, making standard attribution methods ineffective. This is why Steam marketing attribution requires a different approach. Through fingerprinting-based attribution, measurement partners such as Steam Data Suite track user journeys around the Steam ecosystem. When a player clicks a Theorycraft Marketing campaign link, an anonymous identifier is created. The same process occurs when that player launches the game for the first time. Using probabilistic modelling, this data allows us to attribute Steam user acquisition back to specific campaigns, channels, and promotional efforts - enabling accurate Steam Attribution & Optimisation without relying on traditional tracking methods.