Search engine indexing is available in Zulip today via Zulip's public archive tool (https://github.com/zulip/zulip-archive). Many larger OSS projects using Zulip, like Rust, Julia, and Lean Prover, use it.

We expect to have a native feature allowing a configurable set of streams to be browsed using a real Zulip web app UI without creating an account, available in beta in the next few weeks; we're actively integrating the implementation via https://github.com/zulip/zulip/pull/18532.

We plan to look at optional search indexing in that native implementation once the logged-out access feature is complete.