The statewide minimum energy code in Texas is IECC 2015/ASHRAE 90.1-2013. However, some cities (Plano, Austin, etc...) have adopted newer energy codes or have local amendments. Be sure to check the local building codes of the city your project is located in.

I would recommend asking the city plan review department what their requirements are for submitting energy model documentation. Different cities have different requirements, and there is not much standardization across the state.