The core Algol 68 language is indeed set in stone.
But we are carefully adding many GNU extensions to the language, as was explicitly allowed by the Revised Report:
[RR page 52]
"[...] a superlanguage of ALGOL 68 might be defined by additions to
the syntax, semantics or standard-prelude, so as to improve
efficiency or to permit the solution of problems not readily
amenable to ALGOL 68."
The resulting language, which we call GNU Algol 68, is a strict super-language of Algol 68.You can find the extensions currently implemented by GCC listed at https://algol68-lang.org/