We have MPN as RAK3172-T-9-SM-I , If we purchase this then it is sure that it is coming in US 915 Band by default and 4.2.1 Version from manufacturer ?
Yes, it will support US915, but if you want RUI3 V4.2.1, please request it. Factory default is V4.0.6.
If you order from DigiKey or from other distributors, you will get RUI3 V4.0.6 as firmware.