Rust tool Blaze patches edits into cargo binaries and claims up to 92x faster rebuilds

A new open-source tool called Blaze claims to cut Rust rebuild times from seconds to milliseconds by compiling only the functions you changed and patching them into the binary cargo already built. The project, published on GitHub by Indexable and currently on Hacker News' front page, advertises incremental builds up to 92x faster than cargo and rustc, though the averages it reports from real projects are more modest.

A drop-in cargo wrapper

Blaze takes the same commands as cargo with its own name in front: blaze run, blaze test, blaze build. The first build is an ordinary cargo build, after which Blaze spends a few seconds loading the project. From then on, editing a function and building again returns within milliseconds, according to the project's README, and the finished line is tagged [ra-jit] — the engine's name before the project was renamed from ra-jit to Blaze on 2026-10-24. Every other cargo command passes straight through to cargo, and cargo blaze run works as an alias. Installation is via a shell script, crates.io or Nix; the tool downloads its own Rust toolchain once (roughly 100 to 135 MB) or reuses the one from rustup.

The benchmarks

The headline figure is 92x, but the measured averages over real projects that the README reports are 10x on macOS arm64, 24x on Linux aarch64 and 11x on Linux x86-64. Per-project results on Linux x86-64:

Project	cargo build	blaze
ripgrep	508 ms	56 ms (9.1x)
nushell	1.25 s	236 ms (5.3x)
helix	2.15 s	116 ms (19x)
bun (1.25M lines of Rust)	9.11 s	451 ms (20x)

With live edits enabled, the project says a running program picks up new code about 20 ms after you save the file.

How it works

Blaze runs beside cargo and keeps the project compiled in memory. After an edit it recompiles only the changed functions and writes them into the executable cargo already produced, instead of relinking from scratch. Programs that opt in can take the new code while they keep running — the project demonstrates this with a Game of Life whose rules, colours and speed can be changed live on Apple silicon.

The implementation leans on established components: rust-analyzer's analysis and MIR, Cranelift for fast code generation, LLVM via inkwell for the optimised tiers, salsa as the incremental engine, and code from DioxusLabs' rustd. The README is careful to note that none of these projects endorses Blaze.

The caveats

Blaze supports macOS on Apple silicon and Linux; on Windows, every build falls back to cargo. It ships as its own toolchain pinned to a nightly snapshot (blaze-2026-10-25) regardless of what a project pins — both stable code and code using feature gates builds, but your own toolchain and CI remain authoritative. The tool trades memory for speed, consuming a few GB even for a small project. The project describes itself as young and advises keeping cargo check or CI as the final arbiter, and reporting any behaviour that differs from cargo.

Why it matters

Compile times remain one of Rust's most persistent complaints, especially in the edit-build-run loop where a few seconds of relinking breaks concentration. Most prior work has focused on faster linkers or smarter caching; Blaze attacks the problem differently, by reusing cargo's output and hot-patching only what changed. A roughly 20 ms save-to-run latency is the kind of responsiveness that changes how developers iterate, not just how fast CI finishes. The numbers are the project's own and not independently verified, and Indexable says it is already building fast Rust CI and remote builds on top of Blaze with early-access partners — a signal that it sees team-scale build pain, not just local rebuilds, as the opportunity. The tool is dual-licensed under MIT or Apache-2.0 and was built at Indexable for the company's native app.