Cloudflare has turned on Automatic Key Exchange for existing zones and made it the default for new ones. The system probes TLS 1.3 origins, learns which key-agreement algorithms they accept, and leads with the strongest compatible option when Cloudflare opens a new connection to an origin. It prefers the standardized hybrid post-quantum algorithm X25519MLKEM768 when the origin supports it.
What changed
Cloudflare previously began origin handshakes with a static X25519 key share. An origin that preferred another algorithm had to request a retry, adding a network round trip. Automatic Key Exchange now scans active origins about once a day, selects a traffic-weighted preference for the zone, and rolls that preference out in stages while monitoring failures and retry rates. An unhealthy change is rolled back.
The practical consequence
For eligible sites, post-quantum protection on the Cloudflare-to-origin leg can arrive without manual configuration or the latency penalty of a retry. Cloudflare says that, across the scanned cohort in its rollout, the share of origin connections requiring a HelloRetryRequest fell from roughly 52% to 3.7%, reducing p90 handshake latency by more than 150 milliseconds. It also reports that 99.2% of post-quantum TLS 1.3 connections in that cohort now complete in one round trip, while post-quantum origin traffic grew from roughly 25 billion to 45 billion connections per day.
Limits of the protection
This affects only new TLS 1.3 connections between Cloudflare and the origin; browser-to-Cloudflare traffic is a separate connection, and requests that reuse an existing origin connection do not perform another key exchange. The feature requires a compatible encrypted origin mode, does not apply to Cloudflare Tunnel, and cannot add post-quantum capability to an origin that lacks X25519MLKEM768 support. Its preference is currently zone-wide rather than per origin. Post-quantum key agreement also does not provide post-quantum certificate authentication, so it does not close every future quantum attack path.
Configuration caution
Automatic selection is available on all Cloudflare plans and is designed to fall back to a compatible classical algorithm. A separate compliance control can require post-quantum-only or FIPS key agreements. Enforcing a requirement that the origin cannot satisfy can leave no common algorithm and make TLS 1.3 origin connections fail.
Benchmark status
The connection counts, retry rates, and latency improvement are Cloudflare’s measurements from its own rollout cohort. Cloudflare did not publish raw measurements or a reproducible test corpus with the announcement, and DrComps did not independently reproduce the results. Keep-alive traffic is unaffected by the reported handshake improvement.