---
title: New L4 transport telemetry fields in Workers
description: Three new properties on request.cf expose client connection RTT and delivery rate, enabling transport-aware logic in Workers without client-side changes.
image: https://developers.cloudflare.com/changelog-preview.png
---

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## New L4 transport telemetry fields in Workers

Apr 01, 2026 

[ Workers ](https://developers.cloudflare.com/workers/) 

Three new properties are now available on `request.cf` in Workers that expose Layer 4 transport telemetry from the client connection. These properties let your Worker make decisions based on real-time connection quality signals — such as round-trip time and data delivery rate — without requiring any client-side changes.

Previously, this telemetry was only available via the `Server-Timing: cfL4` response header. These new properties surface the same data directly in the Workers runtime, so you can use it for routing, logging, or response customization.

#### New properties

| Property      | Type                | Description                                                                                                                                                              |
| ------------- | ------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| clientTcpRtt  | number \| undefined | The smoothed TCP round-trip time (RTT) between Cloudflare and the client in milliseconds. Only present for TCP connections (HTTP/1, HTTP/2). For example, 22.            |
| clientQuicRtt | number \| undefined | The smoothed QUIC round-trip time (RTT) between Cloudflare and the client in milliseconds. Only present for QUIC connections (HTTP/3). For example, 42.                  |
| edgeL4        | Object \| undefined | Layer 4 transport statistics. Contains deliveryRate (number) — the most recent data delivery rate estimate for the connection, in bytes per second. For example, 123456. |

#### Example: Log connection quality metrics

JavaScript

```

export default {

  async fetch(request) {

    const cf = request.cf;


    const rtt = cf.clientTcpRtt ?? cf.clientQuicRtt ?? 0;

    const deliveryRate = cf.edgeL4?.deliveryRate ?? 0;

    const transport = cf.clientTcpRtt ? "TCP" : "QUIC";


    console.log(`Transport: ${transport}, RTT: ${rtt}ms, Delivery rate: ${deliveryRate} B/s`);


    const headers = new Headers(request.headers);

    headers.set("X-Client-RTT", String(rtt));

    headers.set("X-Delivery-Rate", String(deliveryRate));


    return fetch(new Request(request, { headers }));

  },

};


```

Explain Code

For more information, refer to [Workers Runtime APIs: Request](https://developers.cloudflare.com/workers/runtime-apis/request/).