Given that the interpreter makes system calls directly using inline assembly [1], I suspect that any hope of portability went out the window long ago.
[1]: https://bitbucket.org/ngn/k/src/b54eb5cfea5eb821fe1de68d2a8a...
[1]: https://bitbucket.org/ngn/k/src/b54eb5cfea5eb821fe1de68d2a8a...
across operating systems: it works on linux and freebsd as-is (thanks bakul), and with a few changes on windows+libc (thanks ktye) - https://github.com/ktye/i/tree/master/_/ngn though i personally never use windows