Astral's agent-patched rustc fork speeds up builds as agentic Rust forks proliferate

On Oct 21, Ruff author Charlie Marsh posted a thread surveying a new wave of Rust alternatives/forks that pitch iteration speed as their core selling point — what he calls "agentic Rust forks".

Confirmed

• He named two representative projects: rustd builds on Rust Analyzer, leveraging RA's incremental-analysis-oriented design (using HIR, with MIR for some features), which in theory enables second-scale recompiles after edits; Relax is a Rust JIT that generates native code at runtime, with its own frontend and backend compilers and support for hot reloading.
• Per Marsh, Relax developer rikarends's project has reached 85% coverage of the rustc test suite and is heading toward 100%, with performance approaching LLVM.
• Marsh summarized the common trade-offs of such fast-compile projects: possibly requiring a long-lived stateful daemon, supporting only a subset of Rust, skipping borrow checking or type checking to emit code directly, and slower runtime code.

Not yet confirmed

• Marsh explicitly noted these projects are quite early: he hasn't managed to build Ruff successfully with any of them yet, nor has he read their source code, so conclusions await validation as the projects mature.

Why it matters

• Marsh argues that more noteworthy than any specific project are the ideas these projects explore, and whether those ideas can evolve and flow back into Rust mainline to improve dev-loop speed.

2026-10-21 ~ 2026-10-21 · 12 related posts

• [source] Agentic Rust forks focused on iteration speed are emerging, says Ruff's creator — charliermarsh · 2026-10-21
• Ruff creator: none of the fast-iteration Rust compilers can build Ruff yet — charliermarsh · 2026-10-21
• Four tradeoffs of fast Rust dev loops: stateful daemons, language subsets, skipped checks, slower runtime — charliermarsh · 2026-10-21
• Dev claims 10x faster Rust builds via per-function codegen caching and fine-grained invalidation — charliermarsh · 2026-10-21
• rustd builds on Rust Analyzer's incrementality for near-instant recompiles after edits — charliermarsh · 2026-10-21
• The costs of fast Rust builds: no borrow checker, behavior drift vs rustc, stateful daemons — charliermarsh · 2026-10-21
• [source] Rust JIT project Relax hits 85% of rustc test coverage, closing in on LLVM performance — charliermarsh · 2026-10-21
• Ruff creator surveys fast-iteration Rust compilers: 'there is something to this idea of a JIT for Rust' — charliermarsh · 2026-10-21
• Astral Forks the Entire Rust Toolchain, Lets Agents Optimize It — charliermarsh · 2026-10-21
• [source] Astral's Ohm rustc Fork Cuts Compile Times 38%, cargo check 3x Faster — charliermarsh · 2026-10-21
• Astral's Agent-Optimized rustc Fork Will Be Open Sourced, Author Uses It Daily — charliermarsh · 2026-10-21
• Astral's Agent-Optimized rustc Fork Speeds Up Real Sessions by 30-40% — charliermarsh · 2026-10-21