R5RS and R7RS define = as accepting at least two arguments; it is an error to supply fewer. However, that doesn't forbid Schemes from providing extension behavior. This is an investigation of what Schemes in the suite do with (=) and (= 1):
Returns #t for both (=) and (= 1): MIT, Gambit, Chicken, Guile, SCM, KSi, Sizzle
Signals an error for (=), but returns #t for (= 1): Chez, Vicare, Ypsilon, IronScheme, JScheme, STklos, XLisp, Elk, Llava, SXM
Signals an error for (=), but returns #f for (= 1): FemtoLisp
Signals an error in both cases: Racket, Gauche, Bigloo, Scheme48/scsh, Kawa, SISC, Larceny, Mosh, NexJ, SigScheme, Shoe, TinyScheme, Scheme 9, RScheme, S7, BDC, Rep, Schemik, UMB, Dfsch, Inlab, Oaklisp, Sagittarius, Foment, Picrin, Owl Lisp, Chibi