We introduce shape-changing swarm robots, a new type of computer interface that consist of a swarm of self-transformable robots. These robots can both individually and collectively change their shape to display information, actuate objects, act as tangible controllers, visualize data and provide affordances. To demonstrate this idea, we present ShapeBots, a concept prototype of shape-changing swarm robots. Each robot can change its shape by leveraging small linear actuators that are thin (2.5 cm) and highly extendable (extend up to 20cm) in both horizontal and vertical directions. The modular design of each linear actuator enables various shapes and topologies of self-transformation. We illustrate potential applications scenarios and discuss how this new type of interface can open up new possibilities for the future of ubiquitous and distributed shape-changing interfaces.