[RTL5k](https://sdk.ably.com/builds/ably/specification/main/features/#RTL5k) was added in https://github.com/ably/docs/pull/1044, amended in https://github.com/ably/docs/pull/1160 and then only implemented in a single SDK (https://github.com/ably/ably-js/pull/784). It needs to be implemented in this SDK, as a specification/protocol version 1.2 requirement.
RTL5k was added in ably/docs#1044, amended in ably/docs#1160 and then only implemented in a single SDK (ably/ably-js#784).
It needs to be implemented in this SDK, as a specification/protocol version 1.2 requirement.