[Fundamentals] Changelog: Add 2025-10-16-header-limit-increase.mdx (#25874)

Changelog entry for header increase to 128 KB

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Co-authored-by: Pedro Sousa <[email protected]>

Author: mbullock1986

src/content/changelog/fundamentals/2025-10-16-header-limit-increase.mdx

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+---
+title: Increased HTTP header size limit to 128 KB
+description: Cloudflare's CDN and Workers platform now support up to 128 KB for request and response headers
+date: 2025-10-16
+---
+
+## CDN now supports 128 KB request and response headers 🚀
+
+We're excited to announce a significant increase in the maximum header size supported by Cloudflare's Content Delivery Network (CDN). Cloudflare now supports up to **128 KB** for both **request and response headers**.
+
+Previously, customers were limited to a total of 32 KB for request or response headers, with a maximum of 16 KB per individual header. Larger headers could cause requests to fail with `HTTP 413` (Request Header Fields Too Large) errors.
+
+---
+
+### What's new?
+
+- **Support for large headers:** You can now utilize much larger headers, whether as a single large header up to 128 KB or split over multiple headers.
+- **Reduces `413` and `520` HTTP errors:** This change drastically reduces the likelihood of customers encountering `HTTP 413` errors from large request headers or `HTTP 520` errors caused by oversized response headers, improving the overall reliability of your web applications.
+- **Enhanced functionality:** This is especially beneficial for applications that rely on:
+  - A large number of cookies.
+  - Large Content-Security-Policy (CSP) response headers.
+  - Advanced use cases with Cloudflare Workers that generate large response headers.
+
+This enhancement improves compatibility with Cloudflare's CDN, enabling more use cases that previously failed due to header size limits.
+
+---
+
+To learn more and get started, refer to the [Cloudflare Fundamentals documentation](/fundamentals/reference/connection-limits/#request-limits).