add a changelog entry about Open Next perf improvements (#23277)

Co-authored-by: lrapoport-cf <[email protected]>

Author: 2 people

src/content/changelog/workers/2025-06-05-open-next-size.mdx

@@ -0,0 +1,18 @@
+---
+title: Performance and size optimization for the Cloudflare adapter for Open Next
+description: Update to the latest version of `@opennextjs/cloudflare` to automatically benefit from these improvements.
+products:
+  - workers
+date: 2025-06-05T19:00:00Z
+---
+
+With the release of the Cloudflare adapter for Open Next v1.0.0 in May 2025, we already had followups plans [to improve performance and size](https://blog.cloudflare.com/deploying-nextjs-apps-to-cloudflare-workers-with-the-opennext-adapter/#1-0-and-the-road-ahead).
+
+`@opennextjs/cloudflare` v1.2 released on June 5, 2025 delivers on these enhancements. By removing `babel` from the app code and dropping a dependency on `@ampproject/toolbox-optimizer`, we were able to reduce generated bundle sizes. Additionally, by stopping preloading of all app routes, we were able to improve the cold start time.
+
+This means that users will now see a decrease from 14 to 8MiB (2.3 to 1.6MiB gzipped) in generated bundle size for a Next app created via create-next-app, and typically 100ms faster startup times for their medium-sized apps.
+
+Users only need to update to the latest version of `@opennextjs/cloudflare` to automatically benefit from these improvements.
+
+Note that we published [CVE-2005-6087](https://github.com/opennextjs/opennextjs-cloudflare/security/advisories/GHSA-rvpw-p7vw-wj3m) for a SSRF vulnerability in the `@opennextjs/cloudflare` package.
+The vulnerability has been fixed from `@opennextjs/cloudflare` v1.3.0 onwards. Please update to any version after this one. v1.6.3 is the latest at the time of writing.