Next.js Daily: CSS Chunking Algorithm and Performance Improvements
Four pull requests were merged to Next.js on May 18th, including a major new experimental CSS chunking algorithm for Turbopack and task prioritization improvements. Additional testing infrastructure updates were also completed.
Duration: PT2M1S
Transcript
Good morning. This is Next.js Daily for Monday, May 18th, 2026.
Tobias Koppers merged a significant addition to Turbopack - a new graph-based CSS chunking algorithm available behind the experimental flag `cssChunking: "graph"`. This algorithm models CSS ordering as a weighted DAG and aims to reduce overshipping of CSS while optimizing for shared chunks across pages. The feature is off by default and Turbopack-only, with configurable cost parameters for request overhead and module sizing. Testing on vercel.com shows approximately 3 seconds for the complete chunking pipeline.
Tim Neutkens merged improvements to the test infrastructure, converting more tests from the legacy `createNext` pattern to the newer `nextTestSetup` approach. This continues the ongoing effort to modernize the testing framework across 31 files.
Sokra also merged two performance-focused changes to the Turbopack task system. The first introduces a new "Recomputation" priority level that schedules recomputed tasks ahead of invalidation phases, improving build latency when downstream consumers are waiting for task outputs. The second optimizes the asset emission process by running actual file writes before duplicate checks and parallelizing conflict detection, addressing build time issues that could previously extend to 30 minutes.
Four additional commits landed covering the same changes, with the CSS chunking algorithm representing the largest addition at over 3,200 lines added across 27 files.
What's next: The experimental CSS chunking feature will likely see real-world testing and parameter tuning based on production usage patterns. The ongoing test infrastructure migration should continue with additional test suites being converted.
That's your Next.js update for today. I'm back tomorrow.