Quantum computers won't kill Bitcoin mining. They will kill the signature.

Every chain you use signs transactions with ECDSA, EdDSA or Schnorr. One algorithm breaks all of them: Shor's algorithm, run on a cryptographically relevant quantum computer (CRQC). It recovers the private key from the public key. No brute force, no workaround.

What survives: hashing. Grover's algorithm only halves hash security — SHA-256 goes from 256-bit to 128-bit effective. Mining is fine. PoW is fine.

What dies: signatures. And blockchains have a twist classical crypto doesn't: public keys are already public. Old address types (P2PK, like Satoshi's coins) and reused addresses have exposed pubkeys today. No harvesting needed. The attack is: wait for Q-day, sweep the coins before the owner moves them. Current estimates: 4-7 million BTC sits in exposed addresses.

Estimated qubits needed to break RSA-2048 has collapsed four orders of magnitude in fourteen years — and every revision moves faster than the last.

• Lattice — ML-KEM (Kyber), ML-DSA (Dilithium), Falcon. The workhorse family: smallest signatures, most adoption. Cost: signatures 10-70× bigger than ECDSA's 64 bytes.
• Hash-based — SLH-DSA (SPHINCS+), XMSS, LMS, Winternitz. The most conservative assumptions (only requires hash functions to stay hard). Cost: signatures from 2.5 KB to 49 KB, and stateful schemes (XMSS/LMS) sign exactly once per key. Painful for wallets.
• Code-based — HQC. Backup key exchange, standard expected ~2027.

• Standards: done. FIPS 203/204/205 finalized 2024. Falcon final expected 2026-27.
• The internet: round one complete. TLS with hybrid X25519+ML-KEM is default in Chrome, Firefox, Cloudflare and AWS since 2024-25. Signal (PQXDH) and iMessage (PQ3) too.
• Bitcoin: BIP-360 (P2QRH) merged into the official BIP repo Feb 2026. Testnet live. No soft-fork activation scheduled — still just a proposal, but the first structural step.
• Ethereum: 'lean Ethereum' (Justin Drake, Jul 2025). PQ elevated to top strategic priority Jan 2026 — hash-based everything, leanVM, dropping Poseidon for SHA/BLAKE. Plus the emergency plan: a hard fork that wipes exposed accounts, STARK fallback. All roadmap; execution 2026-2030.
• Algorand: furthest of the big L1s. Falcon-1024 in State Proofs since 2022; PQ transactions on mainnet since Nov 2025 (140K+). Stage 3 'Migration Live' on qrindex.org.
• Solana: opt-in Winternitz Vault (Blueshift, Jan 2025), one-time use. Official 'Quantum Readiness' post Apr 2026; bigger tx sizes coming to fit PQ signatures.
• QRL: the OG. XMSS since 2018. Zond (EVM-compatible, ML-DSA-87) testnet V2 Mar 2026, audits ~50%, mainnet date not set.
• PQ-native chains: Mochimo (WOTS+, 2018), Cellframe (Dilithium + Kyber), QANplatform, Quantus (Poseidon2 PoW + mandatory ML-DSA addresses, mainnet Sep 2026). They don't have to migrate — born safe. A real structural edge, traded against liquidity and team risk.

Scorecard in one line: standardization done, the internet half done, blockchains still at the starting line. The urgency runs on a collapsing qubit clock, not on a real machine.

Look for published assumptions and a security argument. If the pitch is just the phrase 'quantum-proof', walk away — the founders actually building in this space are the first to say so. Today's cohort is micro-caps with bus factor 1 and no audits: options priced like a used car.

Tracker worth bookmarking: [qrindex.org](https://qrindex.org) — ranks every chain's PQ migration stage, updated quarterly.