PathOS is a Horizon Europe project aiming to collect concrete evidence of Open Science effects, study the pathways of Open Science practices, from input to output, outcome and impact, including the consideration of enabling factors and key barriers. The PathOS project has completed 6 case studies that model Open Science pathways, measuring input indicators, costs, and outcomes. These case studies have tested and operationalised Open Science indicators, providing valuable data and expert insights from various local environments. They have also contributed to the Cost-Benefit Analysis and validated key results. Each case study tells a complete story, covering different objectives, implementation mechanisms, and actors across the research and innovation ecosystem.