Does anyone know whether Sonic uses all-beef franks?

I can’t find anything spelling it out, and I hoped maybe a Doper might have worked there or knows something. Thanks.

I don’t know whether this is true of all Sonics, but when a friend of mine worked at a Sonic in my town (Tulsa, Oklahoma), they used all-beef wieners. This was in the late 1990s.

There is a mention of all-beef hot dogs on this Sonic webpage.