Individual firm and ecosystem level efforts are required to meaningfully improve sustainability across the food system. While there has been extensive research on collaboration for sustainability in the food system, these studies focus on working along the supply chain. As the food system is complex with relations and effects spanning across supply chains and industries, another approach is for firms to look beyond their traditional supply chain to tackle sustainability at their ecosystem level. In this regard, there is a need to investigate how firms collaborate with partners to influence sustainability in their ecosystem. In this paper, we present findings of an exploratory study with interviews of 17 firms across the food system that work with partners in their ecosystem for sustainability. We found that informal collaboration among partners is common but occur differently at certain stages of innovation and development and happens even when sharing of benefits are not yet agreed upon. The findings suggest how individual firms can support ecosystem change and how they can work with partners to develop and propagate innovative sustainability solutions in the food system.