Answer
LoRa Basics Modem (LBM) is an open-source LoRaWAN stack and software library that can run on external MCUs. It for example enables worldwide interoperability in the ISM sub-GHz and 2.4 GHz bands and is broadly used by many companies in their LoRaWAN end-node products.
Our AT Interface application and implementation for the RM126x series is utilizing the LoRa Basics Modem SDK version 2.0.1. It is developed and maintained by the Semtech Corporation and also publicly available on GitHub at https://github.com/Lora-net/SWSD001/tree/v2.0.1.