The Pixhawk 4 Mini autopilot is designed for engineers and hobbyists who are looking to tap into the power of Pixhawk 4 but are working with smaller drones. Pixhawk 4 Mini takes the FMU processor and memory resources from the Pixhawk 4 while eliminating interfaces that are normally unused. This allows the Pixhawk 4 Mini to be small enough to fit in a 250mm racer drone. This autopilot is designed and developed in collaboration with Holybro and Auterion. It is based on the Pixhawk FMUv5 design standard optimized to run PX4.
You can read more over on the px4 wiki, but as usual we will be sticking this at our store soon:-)