BTQ’s Bitcoin Quantum Testnet Lays Bare Public‑Key Exposure and Migration Costs

BTQ Technologies has deployed a Bitcoin-compatible test network to exercise post-quantum signature primitives in an environment that mirrors Bitcoin’s operational surface. Rather than claim an imminent cryptographic collapse, the testnet substitutes the elliptic-curve signing method with ML-DSA, a module-lattice approach standardized by NIST, to reveal practical engineering consequences. The most immediate observable consequence is signature bloat: lattice-based signatures increase per-transaction data dramatically, which in BTQ’s design required raising the block limit to 64 MiB to accommodate comparable throughput. Beyond raw size, the experiment recreates wallet flows, transaction verification and mining to measure end-to-end effects on nodes, explorers and pools. The cryptographic threat model the testnet probes remains focused on exposed public keys, because a large, fault-tolerant quantum computer would only be useful for deriving private keys if those public keys are visible onchain. That condition concentrates risk in a small set of legacy output types and in wallets that reuse addresses, so the danger is not uniform across all coins. BTQ’s numbers emphasize scale: certain historical output classes represent a tiny share of UTXOs yet carry outsized value, and the company points to millions of bitcoins that could be treated as exposed under this framing. The testnet therefore functions as a cost-model: it converts abstract algorithmic risk into measurable impacts on blockspace, bandwidth and verification load. This makes it clear that any protocol-level response will be both a coordination and capacity challenge — shifting signature formats affects transaction size, propagation, fee markets and the economics of mining and full-node operation. Proposals that reduce structural exposure without selecting a single post-quantum signer, such as new output encodings that avoid onchain public keys, look attractive because they delay the hardest trade-offs. In short, BTQ’s sandbox does not settle whether quantum machines will break Bitcoin; it clarifies the operational price of preparing for that possibility and the places where defenders should focus observability and migration planning.