Headstart

Overview

Headstart is an experimental patch set for rustc and cargo (PowderworksCode/headstart) that emits .early-rmeta metadata after item interfaces are type-checked — before function bodies finish — allowing dependent crates to compile in parallel.

Recent Developments

• 2026-10-04: Public benchmarks on 13 real projects (rust-analyzer, zed, bevy, polars, wasmtime, lemmy, etc.) report up to 54% faster cargo check and 42% faster cargo build on 16-core machines; gains shrink on 4-core systems (2026-10-04-rust-headstart-faster-builds, 2026-10-04-rust-headstart-terminal-space)
• Enabled via -Zearly-metadata (rustc) and -Zheadstart (cargo), or CARGO_UNSTABLE_HEADSTART=true
• Readiness doc: “Ready for the design conversation” — not yet ready to merge; no license file as of analysis

Related

• rust-compiler-pipelining
• cargo-build-optimization
• rust
• developer-productivity
• rust-build-performance

Sources

• 2026-10-04-rust-headstart-faster-builds
• 2026-10-04-rust-headstart-terminal-space
• 2026-10-04-rust-headstart-gokawiil