0-RTT Connection Resumption

Last updated Oct 16, 2026 Zero round trip time resumption (0-RTT) improves performance for clients who have previously connected to your website, reducing latency for returning users. This feature is especially beneficial for those who frequently visit your application or connect over mobile networks.

We support 0-RTT for GET, HEAD, and OPTIONS requests, facilitating faster responses for these types of requests. Note that 0-RTT is not supported for POST requests.

In line with 0-RTT standards, we add the Early-Data: 1 header to 0-RTT requests, which allows origin servers to identify when a request has used 0-RTT resumption. Customers should be able to see the Early-Data: 1 header for any 0-RTT requests connecting to their origin.

For more information on 0-RTT, including its functionality and potential limitations, refer to our blog post ↗︎.

Availability

Enable 0-RTT Connection Resumption

By default, 0-RTT Connection Resumption is not enabled on your Cloudflare application.

To enable 0-RTT Connection Resumption in the dashboard:

1. In the Cloudflare dashboard, go to the Speed > Settings page. Go to Settings ↗
2. Go to the Protocol Optimization tab and under 0-RTT Connection Resumption, switch the toggle to On.

To adjust your 0-RTT Connection Resumption settings with the API, send a PATCH request with 0rtt as the setting name in the URI path, and the value parameter set to "on" or "off".

Note

The 0-RTT Connection Resumption is only established between the client and Cloudflare. It does not extend to the origin server.

Security considerations

0-RTT reduces latency by allowing requests before the connection handshake completes. By design, these requests can be replayed and, for QUIC, processed before the client source IP address is validated. Before enabling 0-RTT, evaluate whether these risks are compatible with your security requirements.

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