The largest commercial impact of quantum computing, by an order of magnitude, is not the new compute paradigm but the cryptographic transition forced by Shor's algorithm. Every TLS connection, every signed firmware blob, every long-lived signed document is potentially exposed to a future cryptographically-relevant quantum computer (CRQC). Harvest-now-decrypt-later attacks make the calendar urgent even though a CRQC does not yet exist.
The PQC market is forecast at $50B+ cumulative through 2035 (McKinsey, BCG mid-cases). Most of that spend is software services and HSM replacement, not new product sales. The names with shipping PQC products today — Cloudflare, Apple, Google, NIST-aligned vendors — capture the first wave; the names silent at scale (notably Meta, X) are accumulating risk that auditors will start to price.
See /glossary for ML-KEM, ML-DSA, SLH-DSA, HNDL, Q-Day, CNSA 2.0 definitions. See /learn/bb84 for the QKD alternative architecture and the NSA's reasoning for preferring PQC over QKD.