Ethereum established December 2029 as an engineering objective to return resistant to quantum computing its main layer, while preparing Hegotá with programmable transactions, optional tests of execution and new privacy tools. The date does not constitute a guarantee, but it makes postquantic security one of the central commitments of the roadmap.
The Ethereum Foundation has set a December 2029 target for quantum-resistant ETH L1: accounts, consensus, and data layers; details from a September 16 Reddit AMA.