For Japan-coverage IoT SIMs, supported networks differ by subscription plan:
- plan-D: 3G, 4G, and LTE Cat.M1
- plan-DU / plan-K / plan-K2: 4G only
- plan-KM1: LTE Cat.M1 only
Whether a Soracom IoT SIM can use 4G depends on whether your area has 4G coverage. See the Supported Carriers documentation for details. Whether you connect via 4G or 3G is determined by your module's supported methods/frequencies, your location, and signal conditions. The Soracom platform has no feature to lock a SIM to 3G or 4G.