Blazor and .NET 10 breaking changes

funkysi1701@gmail.com (funkysi1701) — Mon, 17 Nov 2025 20:00:00 +0000

What’s New in .NET 10?

.NET 10 was released this week and it is full of awesome new features. Check it out at .NET Download , there is also a new version of Visual Studio which you should also check out.

I quickly upgraded my .NET projects to take advantage of the new version, but my Blazor WebAssembly (Wasm) project encountered the following error in the browser console:

System.NotSupportedException: net_http_synchronous_reads_not_supported
 at System.Net.Http.BrowserHttpReadStream.Read(Byte[] buffer, Int32 offset, Int32 count)
 at System.IO.DelegatingStream.Read(Byte[] buffer, Int32 offset, Int32 count)
 at System.IO.StreamReader.ReadBuffer(Span`1 userBuffer, Boolean& readToUserBuffer)
 at System.IO.StreamReader.ReadSpan(Span`1 buffer)
 at System.IO.StreamReader.Read(Char[] buffer, Int32 index, Int32 count)
 at Newtonsoft.Json.JsonTextReader.ReadData(Boolean append, Int32 charsRequired)
 at Newtonsoft.Json.JsonTextReader.ReadData(Boolean append)
 at Newtonsoft.Json.JsonTextReader.ParseValue()
 at Newtonsoft.Json.JsonTextReader.Read()
 at Newtonsoft.Json.JsonReader.ReadAndMoveToContent()
 at Newtonsoft.Json.JsonReader.ReadForType(JsonContract contract, Boolean hasConverter)
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
 at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
 at Newtonsoft.Json.JsonSerializer.Deserialize(JsonReader reader, Type objectType)
 at Newtonsoft.Json.JsonSerializer.Deserialize[MyResult](JsonReader reader)
 at MyAPI.Client.MyClient.<ReadObjectResponseAsync>d__57`1[[MyAPI.Client.MyResult, MyAPI.Client, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].MoveNext()
 at MyAPI.Client.MyClient.MyAsync(MyRequest body, CancellationToken cancellationToken)

This error was getting thrown on a Blazor Wasm page when it tried to make a call to my API. This worked fine in .NET 9 so my suspicion was this might be a breaking change.

The list of new features for .NET 10 can be found .NET 10 Release Notes

HttpClient Response Streaming: Breaking Change in Blazor

I found the following new feature which I suspect is related to my issue:

HttpClient response streaming enabled by default

In prior Blazor releases, response streaming for HttpClient requests was opt-in. Now, response streaming is enabled by default.

This is a breaking change because calling HttpContent.ReadAsStreamAsync for an HttpResponseMessage.Content (response.Content.ReadAsStreamAsync()) returns a BrowserHttpReadStream and no longer a MemoryStream. BrowserHttpReadStream doesn’t support synchronous operations, such as Stream.Read(Span<Byte>). If your code uses synchronous operations, you can opt-out of response streaming or copy the Stream into a MemoryStream yourself.

To opt-out of response streaming globally, use either of the following approaches:

Add the <WasmEnableStreamingResponse> property to the project file with a value of false:

<WasmEnableStreamingResponse>false</WasmEnableStreamingResponse>

Set the DOTNET_WASM_ENABLE_STREAMING_RESPONSE environment variable to false or 0.

To opt-out of response streaming for an individual request, set SetBrowserResponseStreamingEnabled to false on the HttpRequestMessage (requestMessage in the following example):

requestMessage.SetBrowserResponseStreamingEnabled(false);

For more information, see HttpClient and HttpRequestMessage with Fetch API request options (Call web API article).

How to Fix the Streaming Issue in Blazor

To test out if this was the culprit I added <WasmEnableStreamingResponse>false</WasmEnableStreamingResponse> to my csproj file and sure enough this fixed my issue.

Do check out the docs for a complete list of new features and any other potential breaking changes. .NET 10 Release Notes

2025-11 on Funky Si's Test

Blazor and .NET 10 breaking changes

What’s New in .NET 10?

HttpClient Response Streaming: Breaking Change in Blazor

How to Fix the Streaming Issue in Blazor