Common Lisp seems to tick the boxes. The syntax is stable and it doesn't change. New syntax can be added through extensions (pattern matching, string interpolation, etc). The language is stable, meaning code written in pure CL still runs 20 years later. Then there are de-facto standard libraries (bordeaux-threads, lparallel,…) and other libraries. Implementations continue to be optimized (SBCL, CCL) and to develop core features (package-local-nicknames) and new implementations arise (Clasp, CL on LLVM, notably for bioinformatics). It's been rough at the beginning but a joy so far.
The "very compact, never changing" language will end up not quite expressive, thus prone to boilerplate; look at Go.
Lisps avoid this by building abstractions from the same material as the language itself. Basically no other language family has this property, though JavaScript and Kotlin, via different mechanisms, achieve something similar.
https://github.com/CodyReichert/awesome-cl