Gionee X1s has Android 7.0 Nougat and on top of it, Gionee has used Amigo 4.0 as the user interface.
Yes, Gionee X1s does have the VoLTE support.
No. Gionee X1s does not have the hybrid sim slot. It has 2 dedicated sim card slots and 1 dedicated MicroSD card slot. You can use MicroSD card of up to 256GB with this phone.
Yes, Gionee X1s does have the OTG support.