While the widespread diffusion of experimentalism across sectors and polities is well documented, less is known about the extent of the shift to this non‐hierarchical form of governance, which continues to coexist with traditional hierarchical governance and involves more inclusive rulemaking and revision based on review of alternative implementation experiences. By comparing and process‐tracing electricity and telecommunications regulation in the European Union, we find diversity in experimentalism over time and across two sectors often considered similar. We explain varying degrees of experimentalism with strategic uncertainty and the constellation of preferences, which we label “de facto polyarchy.” Thus, we confirm the emphasis on uncertainty documented in the experimentalist literature, while addressing a conventional critique by also highlighting the relevance of “politics.” Moreover, while corroborating the common spread of experimentalism, we suggest that an analytical framework based on ideal types offers the best route forward to develop comparative analysis of experimentalism and non‐hierarchical forms of governance more broadly.