In reviewing the Gerber RS-274X Format, Extended Gerber Files provide enhancements that handle polygon fill codes, custom apertures, and other features that the RS-274D (Basic Gerber) Format did not. As a result, this format is the preferred format when submitting your Gerber files to Sunstone Circuits, along with your NC Drill file if needed.
In most software packages, you are allowed several choices on which format is generated. See attached images of different software packages and the Extended Gerber option. If you have further questions about your specific software, please reply to this post or contact Sunstone Support with questions and we will do our best to assist you.