# What changed in @shopify/mini-oxygen > 35 changes in @shopify/mini-oxygen 2 to 4 from its official release notes, upgrade guides and advisories: 10 breaking, 5 new APIs and options. Each one cited. Sources checked 2026-11-15. HTML: https://unstale.sh/npm/@shopify/mini-oxygen/ To see which of these apply to a repository, run `npx @unstale/cli init` in it. ## @shopify/mini-oxygen 4 ### Breaking changes - Local development now runs the requested compatibility date, or the newest date supported by the bundled runtime and prints a warning if the requested date is unsupported. (4.3.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.3.0) - MiniOxygen re-exports Response from Miniflare; it is now an undici 7 class instead of an undici 5 class. (4.3.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.3.0) - The file is emitted only during SSR builds. (4.2.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.0) - The skeleton template no longer needs the vite-tsconfig-paths plugin because Vite 8 supports resolve.tsconfigPaths natively. (4.1.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.1.0) - The Customer Account API development flag is stable and ready for production use; it enables tunneling for local OAuth development. (4.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.0.0) ### New APIs and options - An optional override lets developers specify custom worker output paths for preview. (4.2.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.0) - MiniOxygen adds support for the Oxygen compatibility date parameter. (4.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.0.0) - MiniOxygen adds support for Oxygen compatibility flags. (4.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.0.0) ### Behavior and default changes - MiniOxygen re-exports fetch from Miniflare, now using undici 7 instead of undici 5. (4.3.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.3.0) - MiniOxygen re-exports Request from Miniflare; it is now an undici 7 class instead of an undici 5 class. (4.3.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.3.0) - The Oxygen Vite plugin infers a compatibility date from the resolved Hydrogen package when one is not provided. (4.2.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.0) - The Oxygen Vite plugin loads Vite environment variables as Mini Oxygen bindings when plugin options or the Hydrogen CLI provide no env bindings. (4.2.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.0) - Worker-specific resolve conditions apply only to the SSR worker environment, leaving browser/client modules on Vite's normal client conditions. (4.2.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.0) - New Hydrogen projects created with npm create @shopify/hydrogen will default to Vite 8. (4.1.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.1.0) - This environment variable enables the stable Customer Account API development flag. (4.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.0.0) ### Tooling - The command can run the built Oxygen worker in Mini Oxygen. (4.2.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.0) - Mini Oxygen supports Vite 7 and Vite 8 while remaining backwards-compatible with Vite 5+. (4.1.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.1.0) ### Fixes and other changes - The oxygen() Vite plugin now writes oxygen.json in builds using the Vite Environment API, preventing Oxygen from using its fallback compatibility date. (4.3.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.3.0) - Local requests now include the traceparent header, matching the trace context Oxygen sets in production. (4.3.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.3.0) - A failed runtime start fails the current request instead of stopping the dev server, and the next request retries. (4.3.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.3.0) - When the Vite dev server runs over HTTPS, the worker receives a request URL with the https: scheme, so origin-dependent code sees the correct origin during local HTTPS development. (4.2.3) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.3) - MiniOxygen's Vite request conversion now supports HTTP/2 requests. (4.2.2) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.2) - Improves the reliability of local debugger connections. (4.2.1) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.1) - The plugin forwards the top-level Vite setting to the custom SSR environment so tsconfig path aliases resolve at runtime. (4.2.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.2.0) - Fixed defer and streaming in development and preview. (4.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.0.0) - External redirects are returned instead of followed internally, allowing the browser to handle OAuth/PKCE flows. (4.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.0.0) - Fixed the method for proper multi-cookie support. (4.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%404.0.0) ## @shopify/mini-oxygen 3 ### Breaking changes - The default runtime exported from the package is now based on workerd. (3.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%403.0.0) ### New APIs and options - The previous Node.js sandbox runtime is available from this export. (3.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%403.0.0) - A Vite plugin integrates Vite with MiniOxygen by running application code within a worker. (3.0.0) — [release notes](https://github.com/Shopify/hydrogen/releases/tag/%40shopify/mini-oxygen%403.0.0) ## @shopify/mini-oxygen 2 ### Breaking changes - Support for the JSON based configuration file is dropped. (2.0.0) — [release notes](https://github.com/Shopify/hydrogen/blob/HEAD/packages/mini-oxygen/CHANGELOG.md) - The oxygen-gen-config command no longer exists. (2.0.0) — [release notes](https://github.com/Shopify/hydrogen/blob/HEAD/packages/mini-oxygen/CHANGELOG.md) - Mini Oxygen can no longer be used in a standalone fashion. (2.0.0) — [release notes](https://github.com/Shopify/hydrogen/blob/HEAD/packages/mini-oxygen/CHANGELOG.md) - The preview function is renamed to startServer, which is now a named export. (2.0.0) — [release notes](https://github.com/Shopify/hydrogen/blob/HEAD/packages/mini-oxygen/CHANGELOG.md) ### Behavior and default changes - Mini Oxygen is now built as an ESM module. (2.0.0) — [release notes](https://github.com/Shopify/hydrogen/blob/HEAD/packages/mini-oxygen/CHANGELOG.md)