AWS D1.1:2015, section 1.2 - Limitations-
"The code was specifically developed for welded steel structures that utilize carbon or low alloy steels that are 1/8 in [3 mm] or thicker with a minimum specified yield strength of 100 ksi [690 MPa] or less. The code may be suitable to govern structural fabrications outside the scope of the intended purpose. However, the Engineer should evaluate such suitability, and based upon such evaluations, incorporate into contract documents any necessary changes to code requirements to address the specific requirements of the application that is outside the scope of the code."

AWS D1.3:2018, section 1.1 Scope -
"This code contains the requirements for arc welding of structural sheet/strip steels, including cold formed members,
hereafter collectively referred to as “sheet steel,” which are equal to or less than 3/16 in [5 mm] in nominal thickness. In
addition, welding hollow structural section (HSS) also called tubular members with wall thickness less than 1/8 in [3 mm]
are included in the scope of this code. Design requirements for HSS member connections are not in the scope of this code."

D1.3 also has provisions for welding sheet to structural members.

Which code to use is dependent on not just material thickness and type, but also end use. This decision is is to be made by the Engineer and/or contract documents.