Add breaking change documentation for NUGET_ENABLE_ENHANCED_HTTP_RETRY removal (#46927)

* Initial plan

* Add breaking change documentation for NUGET_ENABLE_ENHANCED_HTTP_RETRY removal

Co-authored-by: gewarren <[email protected]>

* human edits

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: gewarren <[email protected]>

Author: Copilot

docs/core/compatibility/10.0.md

@@ -82,6 +82,7 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
 | [NU1510 is raised for direct references pruned by NuGet](sdk/10.0/nu1510-pruned-references.md) | Source incompatible | Preview 1 |
 | [PackageReference without a version raises an error](sdk/10.0/nu1015-packagereference-version.md) | Behavioral change | Preview 6 |
 | [HTTP warnings promoted to errors in `dotnet package list` and `dotnet package search`](sdk/10.0/http-warnings-to-errors.md) | Behavioral/source incompatible change | Preview 4 |
+| [NUGET_ENABLE_ENHANCED_HTTP_RETRY environment variable removed](sdk/10.0/nuget-enhanced-http-retry-removed.md) | Behavioral change | Preview 6 |
 
 ## Windows Forms
 

docs/core/compatibility/sdk/10.0/nuget-enhanced-http-retry-removed.md

@@ -0,0 +1,38 @@
+---
+title: "Breaking change: NUGET_ENABLE_ENHANCED_HTTP_RETRY environment variable removed"
+description: "Learn about the breaking change in .NET 10 where NUGET_ENABLE_ENHANCED_HTTP_RETRY environment variable no longer disables exponential retry."
+ms.date: 06/24/2025
+ai-usage: ai-assisted
+ms.custom: https://github.com/dotnet/docs/issues/46537
+---
+# NUGET_ENABLE_ENHANCED_HTTP_RETRY environment variable removed
+
+The `NUGET_ENABLE_ENHANCED_HTTP_RETRY` environment variable no longer has any effect in .NET 10. Previously, this environment variable could be used to disable exponential retry back-off for failed HTTP calls in NuGet operations.
+
+## Version introduced
+
+.NET 10 Preview 6
+
+## Previous behavior
+
+When the `NUGET_ENABLE_ENHANCED_HTTP_RETRY` environment variable was set to `false`, NuGet used the old retry behavior with a fixed 200ms delay between failed HTTP calls instead of exponential back-off.
+
+## New behavior
+
+The `NUGET_ENABLE_ENHANCED_HTTP_RETRY` environment variable has no effect. NuGet always uses exponential retry back-off for failed HTTP calls, which has been the default behavior since .NET SDK 6.0.300.
+
+## Type of breaking change
+
+This is a [behavioral change](../../categories.md#behavioral-change).
+
+## Reason for change
+
+Exponential retry back-off has been the default behavior for nearly 4 years since .NET SDK 6.0.300. The feature was introduced to help when restores overwhelmed servers that couldn't handle all package requests, and exponential retry allowed these requests to succeed. Since there has been no feedback indicating issues with this approach, the fallback option has outlived its utility.
+
+## Recommended action
+
+No action is required.
+
+## Affected APIs
+
+None.

docs/core/compatibility/toc.yml

@@ -82,6 +82,8 @@ items:
                 href: sdk/10.0/nu1015-packagereference-version.md
               - name: HTTP warnings promoted to errors in package list and search
                 href: sdk/10.0/http-warnings-to-errors.md
+              - name: NUGET_ENABLE_ENHANCED_HTTP_RETRY environment variable removed
+                href: sdk/10.0/nuget-enhanced-http-retry-removed.md
           - name: Windows Forms
             items:
               - name: API obsoletions