You may remember this blog post from last year:

The Rust community has had a presence on Mozilla’s IRC network almost since Rust’s inception. Over time, the single channel grew into a set of pretty active channels where folks would come to ask Rust questions, coordinate work on Rust itself, and just in general chat about Rust. Mozilla recently announced that it would be shutting down its IRC network, citing a growing maintenance and moderation burden. They are looking into new options for the Mozilla community, but this does leave the question open as to what the Rust project will do. […]

Since then most Rust project-related synchronous text communication has moved to either Zulip or Discord. The Library team however had remained in the #rust-libs channel on IRC.

With the shut down of Mozilla’s IRC network approaching (see Next steps in https://discourse.mozilla.org/t/synchronous-messaging-at-mozilla-the-decision/50620) we’ve finally decided to move to Zulip, joining the Language and Compiler teams. The t-libs stream is now available at https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs

Feel free to join questions or discussion of the standard library, crates under github.com/rust-lang, or project support for the ecosystem.