Bitcoin's Post-Quantum Upgrade May Break Scalability Assumptions

The crypto industry is facing a daunting challenge as it transitions to a post-quantum future. According to a new report from quantum-secure blockchain project Quantus, Bitcoin and other legacy chains may struggle to migrate before quantum hardware reaches dangerous capability thresholds.

The report warns that the industry's biggest problem is no longer whether quantum computers will eventually break classical cryptography, but rather whether decentralized networks can coordinate a migration to post-quantum systems without overwhelming scalability limits, wallet infrastructure, and governance processes.

Bitcoin's transition to post-quantum systems could be particularly problematic. A standard Bitcoin transaction using ECDSA signatures carries approximately 97 bytes of signature and public key data. In contrast, a comparable transaction using ML-DSA-87 would carry around 7,187 bytes, representing a roughly 74-fold increase.

This increase in signature size could sharply reduce transaction capacity per block unless Bitcoin undergoes deeper architectural changes beyond a simple cryptographic swap. The report argues that this creates a new version of the blockchain trilemma for the post-quantum era.