curl/docs/EXPERIMENTAL.md

Experimental

Some features and functionality in curl and libcurl are considered EXPERIMENTAL.

Experimental support in curl means:

1. Experimental features are provided to allow users to try them out and provide feedback on functionality and API etc before they ship and get "carved in stone".
2. You must enable the feature when invoking configure as otherwise curl is not built with the feature present.
3. We strongly advise against using this feature in production.
4. We reserve the right to change behavior of the feature without sticking to our API/ABI rules as we do for regular features, as long as it is marked experimental.
5. Experimental features are clearly marked so in documentation. Beware.

Graduation

1. Each experimental feature should have a set of documented requirements of what is needed for that feature to graduate. Graduation means being removed from the list of experiments.
2. An experiment should NOT graduate if it needs test cases to be disabled, unless they are for minor features that are clearly documented as not provided by the experiment and then the disabling should be managed inside each affected test case.

Experimental features right now

HTTP/3 support (non-ngtcp2 backends)

Graduation requirements:

• The used libraries should be considered out-of-beta with a reasonable expectation of a stable API going forward.

• Using HTTP/3 with the given build should perform without risking busy-loops

The Rustls backend

Graduation requirements:

• a reasonable expectation of a stable API going forward.

ECH

Use of the HTTPS resource record and Encrypted Client Hello (ECH) when using DoH

Graduation requirements:

• ECH support exists in at least one widely used TLS library apart from BoringSSL and wolfSSL.

• feedback from users saying that ECH works for their use cases

• it has been given time to mature, so no earlier than April 2025 (twelve months after being added here)