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Rspack 2.2.9 Improves Chunking to Cut Duplicate Modules and Shrinks Its Native Binary by 2.13 MB

Rspack 2.2.9, released October 13, reworks code-splitting to reduce duplicated modules and trims its native binary by 2.13 MB through an SWC upgrade.

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Overview

Rspack, the Rust-based JavaScript bundler, published version 2.2.9 on October 13, 2026, according to its GitHub release page. The release is headlined by two changes: an improved code-splitting algorithm intended to produce smaller bundles, and a smaller native binary. The release notes state that “Rspack’s chunking algorithm has been improved to reduce duplicate modules across chunks.”

What Changed

Chunking: fewer duplicated modules

The chunking work comes from pull request #15885, authored by JSerFeng and merged on October 9. The pull request describes the problem this way: “Late reuse of a named async chunk can leave modules duplicated in its descendants.” Its example is a graph in which a child chunk is discovered before a second parent chunk is merged in; the child should then inherit the module supplied by the merged parent instead of carrying its own copy.

According to the pull request, the change keeps ordinary merging intersection-only and, after the existing queues settle, unions pending additions in a separate step. The author writes that separating these phases prevents growth and shrinkage from oscillating around cycles. Duplicate copies are deleted only when every consumer can inherit the module.

The pull request reports measurements on a test application named app-flow-chat. Client JavaScript and CSS size under Brotli fell from 42,569,778 to 41,717,715 bytes, which the author puts at about 2.00%. Physical chunks fell from 1,921 to 1,890, and JavaScript and CSS files from 2,526 to 2,482. The same pull request attaches caveats: those figures came from an earlier commit, and “These whole-build measurements were not rerun for the final convergence/CSS fixes and are not first-screen measurements.” The author also notes that CodSpeed measurements of the chunk-graph build “did not establish a reliable speedup or regression.”

A 2.13 MB smaller native binary

The release notes say Rspack upgraded browserslist-rs and enabled deflate compression for its browser data, “reducing native binary by 2.13 MB (3.08%).” That change rides on pull request #16009, authored by LingyuCoder and merged by chenjiahan on October 8, which upgrades swc_core from 79.0.0 to 82.0.0.

The pull request’s stated motivation is a crash: “Enabling React Compiler can overflow the native stack on long expressions, including files that contain no React code.” The SWC upgrade brings in an upstream fix, and the pull request adds a regression test built from a 1,000-term expression. It also shares the browserslist-rs 0.21.2 dependency with SWC, removing duplicated Browserslist code and data.

Side Effects Documented in the Upgrade

The SWC upgrade pull request includes a breaking-change audit that lists several output-level effects:

  • Refreshed browser data means the default CSS query now resolves Android 151 instead of 150, and four stats test cases had their hashes refreshed as a result.
  • A reverted upstream optimization means some property reads and destructuring are now retained, “potentially increasing output size.”
  • With HtmlRspackPlugin minification enabled, adjacent <script> elements now remain separate rather than being merged.

On plugins, the author states: “This upgrade does not break the Wasm plugin ABI or AST schema.” The pull request says the same prebuilt @swc/plugin-remove-console 14.0.0 binary ran successfully on both Rspack 2.2.8 and the upgraded build.

Rest of the Release

Beyond the two headline items, the release notes list 18 entries under Performance, covering areas such as lazy module source-map materialization, watcher analysis and cache restoration, along with bug fixes for types, CSS handling, lazy compilation and module concatenation. The release credits five first-time contributors.

What We Don’t Know

  • The roughly 2.00% bundle-size reduction was measured on one application at an earlier commit, per the pull request, and was not re-run for the final code. How it generalizes to other projects is not reported in the cited sources.
  • The cited sources do not give a build-time benchmark for the new chunking logic; the pull request says its CodSpeed results were inconclusive.