Second brief in the Net Zero Futures Research Series. Traces a four-stage co-benefits ambition cascade — from what governance frameworks propose, to what cities include in strategies, to what gets reported to CDP, to what is actually measured — across 10 Mission cities' Climate City Contracts (CCCs). Finds that of 712 co-benefits identified across ten cities' action plans, only 41% aligned with NetZeroCities impact framework indicators, and that social, equity, health, biodiversity, governance, and finance co-benefits are not measured as impact indicators at the global reporting level. At the cascade's end, analysis of 92 Mission cities’ CCCs shows most co-benefits remain at the consideration level—without definitions, units of measure, or explicit monitoring. Examines the Energy Access and Poverty Pillar (EAPP) as a case study in non-integration between reporting architectures. Reflects these examples point to structural design issues, local contextual factors, and methodological and institutional gaps. Argues that win-win co-benefits narratives that obscure trade-offs erode long-term governance legitimacy. Introduces the Four Functions Model — co-benefits as compliance, economies of scale, theories of change, and advocacy/communications — to map how cities use co-benefits in climate governance and where transformational gains can be made.