Is there any production ready implementation out there?

ZKP is integrated in Google Wallet and has been running in production for a few months. We (Google) released the ZKP library as open source last year (this is the library used in production).

Announcement: https://blog.google/innovation-and-ai/technology/safety-secu...

Library: https://github.com/google/longfellow-zk

Paper: https://eprint.iacr.org/2024/2010

Afterwards, folks from ISRG produced an independent implementation https://github.com/abetterinternet/zk-cred-longfellow with our blessing and occasional help. I don't know if the authors would call it "production ready" yet, but it is at least code complete, fast enough, and interoperable with ours.