[LazyPup]

Both the International Residential Code and the Uniform Plumbing Code require SDC (Seismic Design Category) strapping and flex lines in specific regions that are subject to seismic activity (earthquakes) or hurricanes, but it is not required in all locations.

in fact, in my location all Gas connections MUST BE piped the full distance and flex lines are prohibited.

When in doubt, contact your local code enforcement authority to determine what the local code requires.