Rules - New QUIC RTT and delivery rate fields

Two new fields are now available in rule expressions that surface Layer 4 transport telemetry from the client connection. Together with the existing cf.timings.client_tcp_rtt_msec field, these fields give you a complete picture of connection quality for both TCP and QUIC traffic — enabling transport-aware rules without requiring any client-side changes. Previously, QUIC RTT and delivery rate data was only available via the Server-Timing: cfL4 response header. These new fields make the same data available directly in rule expressions, so you can use them in Transform Rules, WAF Custom Rules, and other phases that support dynamic fields. New fields Field Type Description cf.timings.client_quic_rtt_msec Integer The smoothed QUIC round-trip time (RTT) between Cloudflare and the client in milliseconds. Only populated for QUIC (HTTP/3) connections. Returns 0 for TCP connections. cf.edge.l4.delivery_rate Integer The most recent data delivery rate estimate for the client connection, in bytes per second. Returns 0 when L4 statistics are not available for the request. Example: Route slow connections to a lightweight origin Use a request header transform rule to tag requests from high-latency connections, so your origin can serve a lighter page variant: Rule expression: cf.timings.client_tcp_rtt_msec > 200 or cf.timings.client_quic_rtt_msec > 200 Header modifications: Operation Header name Value Set X-High-Latency true Example: Match low-bandwidth connections cf.edge.l4.delivery_rate > 0 and cf.edge.l4.delivery_rate < 100000 For more information, refer to Request Header Transform Rules and the fields reference .