A complicated-subsystem team builds and maintains a part of the system requiring specialist knowledge. A defining feature is that majority of team members must possess this specialist knowledge in order to participate1. The goal is to reduce the cognitive load of stream-aligned teams by abstracting away the complexity.
The complicated-subsystem team must work closely with stream-aligned teams during exploration and discovery in early phases and shift to interface and feature evolution during later stages.
1. Skelton, M., Pais, M. & Malan, R. Team Topologies: Organizing Business and Technology Teams for Fast Flow. (IT Revolution Press, Portland, OR, 2019).