All Control Hubs feature an internal IMU. If your Expansion Hub was purchased BEFORE December 2021, it has an internal IMU installed.
There are a few options that will work for giving your Hub Gyro/IMU function.
navX2 Sensor Bundle - Also supported in the FTC programming environment. Code examples are listed on AndyMark's page, and this product includes the correct cables to use within FTC.
Adafruit 9-DOF Absolute Orientation IMU - This is the same IMU as in Control Hubs from before 2022, but will require you to either create an adapter cable or solder a cut sensor cable to the board. Plugging this in and configuring the IMU on I2C port zero will allow you to use and program the same as an internal IMU.
Integrating Gyro with our Logic Level Converter and Sensor Cable Adapter - This is supported in the FTC Programing environment but is just a single-axis gyro, not a full IMU.