# facebook/stylex · RepoSense Release & Migration Intelligence

> [devtools-extension] Fix panel CSS, dedupe rules, and add. Review breaking API changes before upg… Migration: Moderate.

## Metadata
- **Repository URL**: https://github.com/facebook/stylex
- **Primary Package**: `@stylexjs/stylex` (NPM)
- **Categories**: `STYLING`, `BUILD_TOOL`
- **Latest Version**: `v0.19.1`
- **Semantic Status**: `BREAKING`
- **Bundle Size Impact (unavailable)**: `Size Unavailable`
- **Atom Ingestion Feed**: https://github.com/facebook/stylex/releases.atom

## The Human Context (Plain-English Pitch)
@stylexjs/stylex is an open-source library and developer tool in the facebook/stylex ecosystem. It saves developers from writing repetitive low-level boilerplate from scratch by providing a battle-tested, open-source implementation ready for production.

## Stage 1 Executive Summary ([Core Change] + [Required Action] + [Migration Effort])
[devtools-extension] Fix panel CSS, dedupe rules, and add. Review breaking API changes before upg… Migration: Moderate.

## Breaking Changes & Required Actions
- [BREAKING] [babel-plugin] Deterministic ordering for px min/max-width `defineConsts` breakpoints by @henryqdineen in #1652
- [BREAKING] Remove property-prefixed debug class names by @nmn in #1834
- [devtools-extension] Fix panel CSS, dedupe rules, and add metadata export by @mellyeliu in #1721
- [devtools] Improvements to the DevTools extension and expansion to all browsers by @nmn in #1822
- [eslint-plugin] Allow type exports in `enforce-extension` rule by @henryqdineen in #1743
- [eslint-plugin] Accept numeric values for grid line properties by @ahmedsadid in #1730

## Migration Snippet
```ts
npm install @stylexjs/stylex@0.19.1
```

## Ecosystem Compatibility Matrix & Graph Warnings
- **TypeScript 5.x** [`COMPATIBLE`]: Ships standard TypeScript declaration files without type regressions.

## Zero-Noise Release Timeline
- **v0.19.1** (2026-09-15) [BREAKING]: [devtools-extension] Fix panel CSS, dedupe rules, and add. Review breaking API changes before upg… Migration: Moderate.

## Upgrade & Migration Q&A (GEO Direct Answers)
### Is facebook/stylex v0.19.1 safe to upgrade in production?
facebook/stylex v0.19.1 is classified as BREAKING (PATCH release). [devtools-extension] Fix panel CSS, dedupe rules, and add. Review breaking API changes before upg… Migration: Moderate.

### What breaking changes or compatibility risks exist in facebook/stylex v0.19.1?
[babel-plugin] Deterministic ordering for px min/max-width `defineConsts` breakpoints by @henryqdineen in #1652 Remove property-prefixed debug class names by @nmn in #1834

### What is the bundle size impact of @stylexjs/stylex v0.19.1?
Measured bundle size telemetry is currently unavailable for @stylexjs/stylex v0.19.1; verify build output locally before deploying.

### How do I upgrade @stylexjs/stylex to v0.19.1?
Upgrade @stylexjs/stylex to v0.19.1 by running "npm install @stylexjs/stylex@0.19.1" and applying the migration steps: npm install @stylexjs/stylex@0.19.1