Flexumers4Future (F4F) is piloting flexible district heating consumption. In the future, sustainable energy system production and consumption must be better integrated to maximize the utilization of renewable energy, reduce costs, and increase the security of supply. Demand side flexibility is crucial to enabling the planned electrification of the heat sector and adjusting to fluctuations in energy production based on wind and solar energy. HOFOR is, together with the City of Copenhagen, testing a flexumer concept, where customers voluntarily contribute to system flexibility. Flexumers are defined as customers who actively contribute to a sustainable, secure, and affordable energy supply by offering thermal flexibility from their buildings to the district heating (DH) system. The project has proven quite successful, being able to activate up to around 10 MW of flexibility through voluntary agreements --- sufficient to deliver “proof-of-concept” .