Tezos developers are leading the way.

Tezos ecosystem developers have launched a prototype private blockchain payment testnet called TzEL, aimed at resisting future quantum attacks. The prototype combines post-quantum cryptography and zk-STARK proofs to protect transaction data and payment metadata, preventing "collect first, decrypt later" attacks, and alleviating the approximately 300KB proof size issue through a data availability layer. TzEL is currently running on the Tezos testnet and is in the early stages of development, with the transition to quantum resistance still in its infancy.