OCaml 5.1.0 is still a relatively experimental release compared to the OCaml 4.14 branch. Some of the highlights in OCaml 5.1.0 are:

• Many runtime performance regression and memory-leaks fixes (dynlinking, weak array, weak hash sets, GC with idle domains, GC prefetching).
• Restored support for native code generation on RISC-V and s390x architectures.
• Restored Cygwin port.
• Reduced installation size (50% reduction)
• Compressed compilation artefacts (.cmi, .cmt, .cmti, .cmo, .cma files)
• 19 error message improvements
• 14 standard library functions made tail-recursive with Tail-Recursion-Modulo-Cons (TRMC), such as List.append and List.map.
• 57 new standard library functions
• More examples in the standard library documentation
• 42 bug fixes