# Flags SDK 4.2.1

- Product: Flags SDK (https://whatsnew.fyi/product/flags-sdk)
- Vendor: Vercel
- Date: 2026-07-20
- Version: 4.2.1
- Original notes: https://github.com/vercel/flags/releases/tag/flags%404.2.1
- Permalink: https://whatsnew.fyi/product/flags-sdk/releases/4.2.1

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

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- **fixed** — Allow passing a NextRequest or Web Request directly to flag(req) and evaluate(flags, req) outside App Router, fixing empty headers when NextRequest was passed to a flag

###### Patch Changes

-   [#434](https://github.com/vercel/flags/pull/434) [`4d6eb10`](https://github.com/vercel/flags/commit/4d6eb10705ab5aa97baac2fc6f50b85a84c4368a) Thanks [@dferber90](https://github.com/dferber90)! - Allow passing a `NextRequest` / Web `Request` directly to `flag(req)` and `evaluate(flags, req)` outside App Router (e.g. in routing middleware).

    Previously only a Pages Router `IncomingMessage`, or a manually-flattened headers object, worked when calling a flag directly — passing a `NextRequest` produced empty headers because it wasn't recognized as already having a `Headers` instance.