The rustc-builds-alt directory in rust-lang-ci2 (example url ) contains per-commit artifacts of rustc with LLVM assertions enabled (this 'flipped' in 2017 ).
These buckets are for temporary artifacts  and previously there has been discussion about making it easier to consume arbitrary rustc 'channels'  but this has never come to fruition - the alt builds remain almost totally undiscoverable which indicates that it's likely nobody use them (even crater doesn't !).
As a result, the infra team would like to stop producing alt builds (for storage cost and CI time reasons). If you have thoughts on this, we'd love to hear from you