Rust 1.28.0 is released on Thursday and builds are available now for testing. Release artifacts are uploaded to dev (dev-static.rust-lang.org) currently and will be promoted to prod (static.rust-lang.org) this Thursday. The URL is https://dev-static.rust-lang.org/dist/2018-07-31/.
You can test rustup with
RUSTUP_DIST_SERVER=https://dev-static.rust-lang.org rustup update stable
Please let us know if you run into any issues! Pending any detected regressions these are likely to be the exact artifacts that we’ll release on Thursday.
Release notes can be found here.