Claude code developed Kaappi Scheme as directed by Baiju Muthukadan.  (I
don't know whether that sentence completely captures the intricacies of
the relationship.)

I don't know whether I can recommend Kaappi as a whole, but Baiju has
been very responsive to my posts about anomalies I found in Kaappi's
implementation of SRFI 231, and as of now all my SRFI 231 tests pass in
Kaappi with its SRFI 231 implementation.

There are some limitations: It defines u1-storage-class and
f16-storage-class to be #f (which is allowed) and it doesn't catch all
error conditions as soon as possible, which is OK (and is a property
shared by Chibi's implementation).

Kaappi's SRFI 231 implementation is written completely in R7RS small
(the SRFI's sample implementation uses some Gambitisms), so I think it
can be useful to people who would like to have a portable SRFI 231
implementation.

You can find Kaappi Scheme with its SRFI 231 implementation here:

https://github.com/kaappi/kaappi

Brad