Clarify Blazor WASM environment config for >=10.0 (#37043)

Author: guardrex

aspnetcore/migration/90-to-100.md

@@ -3,7 +3,7 @@ title: Migrate from ASP.NET Core in .NET 9 to ASP.NET Core in .NET 10
 author: wadepickett
 description: Learn how to migrate an ASP.NET Core in .NET 9 to ASP.NET Core in .NET 10.
 ms.author: wpickett
-ms.date: 11/10/2025
+ms.date: 04/22/2026
 uid: migration/90-to-100
 ---
 # Migrate from ASP.NET Core in .NET 9 to ASP.NET Core in .NET 10

aspnetcore/migration/90-to-100/includes/blazor.md

@@ -6,7 +6,7 @@ For new feature coverage, see <xref:aspnetcore-10>.
 
 *This section only applies to standalone Blazor WebAssembly apps.*
 
-The `Properties/launchSettings.json` file is no longer used to control the environment in standalone Blazor WebAssembly apps.
+The `Blazor-Environment` header and `Properties/launchSettings.json` file (`ASPNETCORE_ENVIRONMENT` environment variable) are no longer used to control the environment in standalone Blazor WebAssembly apps.
 
 Set the environment with the `<WasmApplicationEnvironmentName>` property in the app's project file (`.csproj`).
 

aspnetcore/release-notes/aspnetcore-10.0.md

@@ -5,7 +5,7 @@ author: wadepickett
 description: Learn about the new features in ASP.NET Core in .NET 10.
 ms.author: wpickett
 ms.custom: mvc
-ms.date: 04/15/2026
+ms.date: 04/22/2026
 uid: aspnetcore-10
 ---
 # What's new in ASP.NET Core in .NET 10

aspnetcore/release-notes/aspnetcore-10/includes/blazor.md

@@ -233,7 +233,7 @@ For more information, see <xref:blazor/fundamentals/static-files?view=aspnetcore
 
 ### Set the environment in standalone Blazor WebAssembly apps
 
-The `Properties/launchSettings.json` file is no longer used to control the environment in standalone Blazor WebAssembly apps.
+The `Blazor-Environment` header and `Properties/launchSettings.json` file (`ASPNETCORE_ENVIRONMENT` environment variable) are no longer used to control the environment in standalone Blazor WebAssembly apps.
 
 Starting in .NET 10, set the environment with the `<WasmApplicationEnvironmentName>` property in the app's project file (`.csproj`).