H1B: Do I need to wait until after October 1 to fill out the DS-160 form and book an appointment, or can I submit it and book an appointment before th

Since you intend to return and be visaed with the H-1B in Vietnam in December, I see no reason why you cannot fill out the DS-160, submit it, and schedule your visa interview before October 1. A consular officer should just be concerned with whether you are qualified on the date of interview, not whether the H-1B had come into effect at the time that you submitted the DS-160. Due to the limitations of the Lawyers.com Forums, Alan Lee & Arthur Lee, Esqs.’ (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.

You do not have to wait till October 1st to fill out a Ds-160 and schedule an appoitnment. However, make sure that your appoinment is on or after Oct 1st.  This answer is intended for informational and educational purposes only and should not be considered legal advice nor forming the attorney client relationship. For initial consultation, call at 480-467-3188 or email at admin@cronuslaw.com.