diff --git a/dotnet/src/Microsoft.Agents.AI.Foundry/Hosting/ServiceCollectionExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Foundry/Hosting/ServiceCollectionExtensions.cs
index e3ff61ad0c..7f01e5904c 100644
--- a/dotnet/src/Microsoft.Agents.AI.Foundry/Hosting/ServiceCollectionExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Foundry/Hosting/ServiceCollectionExtensions.cs
@@ -1,7 +1,11 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Reflection;
+using System.Threading.Tasks;
 using Azure.AI.AgentServer.Responses;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
@@ -89,6 +93,56 @@ public static class FoundryHostingExtensions
     {
         ArgumentNullException.ThrowIfNull(endpoints);
         endpoints.MapResponsesServer(prefix);
+
+        if (endpoints is IApplicationBuilder app)
+        {
+            // Ensure the middleware is added to the pipeline
+            app.UseMiddleware<AgentFrameworkUserAgentMiddleware>();
+        }
+
         return endpoints;
     }
+
+    private sealed class AgentFrameworkUserAgentMiddleware(RequestDelegate next)
+    {
+        private static readonly string s_userAgentValue = CreateUserAgentValue();
+
+        public async Task InvokeAsync(HttpContext context)
+        {
+            var headers = context.Request.Headers;
+            var userAgent = headers.UserAgent.ToString();
+
+            if (string.IsNullOrEmpty(userAgent))
+            {
+                headers.UserAgent = s_userAgentValue;
+            }
+            else if (!userAgent.Contains(s_userAgentValue, StringComparison.OrdinalIgnoreCase))
+            {
+                headers.UserAgent = $"{userAgent} {s_userAgentValue}";
+            }
+
+            await next(context).ConfigureAwait(false);
+        }
+
+        private static string CreateUserAgentValue()
+        {
+            const string Name = "agent-framework-dotnet";
+
+            if (typeof(AgentFrameworkUserAgentMiddleware).Assembly.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion is string version)
+            {
+                int pos = version.IndexOf('+');
+                if (pos >= 0)
+                {
+                    version = version.Substring(0, pos);
+                }
+
+                if (version.Length > 0)
+                {
+                    return $"{Name}/{version}";
+                }
+            }
+
+            return Name;
+        }
+    }
 }
diff --git a/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/Hosting/UserAgentMiddlewareTests.cs b/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/Hosting/UserAgentMiddlewareTests.cs
new file mode 100644
index 0000000000..64f7458852
--- /dev/null
+++ b/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/Hosting/UserAgentMiddlewareTests.cs
@@ -0,0 +1,134 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Net.Http;
+using System.Text.RegularExpressions;
+using System.Threading.Tasks;
+using Microsoft.Agents.AI.Foundry.Hosting;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Hosting.Server;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.TestHost;
+using Microsoft.Extensions.DependencyInjection;
+using Moq;
+
+namespace Microsoft.Agents.AI.Foundry.UnitTests.Hosting;
+
+/// <summary>
+/// Tests for the <c>AgentFrameworkUserAgentMiddleware</c> registered by
+/// <see cref="FoundryHostingExtensions.MapFoundryResponses"/>.
+/// </summary>
+public sealed partial class UserAgentMiddlewareTests : IAsyncDisposable
+{
+    private const string VersionedUserAgentPattern = @"agent-framework-dotnet/\d+\.\d+\.\d+";
+
+    private WebApplication? _app;
+    private HttpClient? _httpClient;
+
+    public async ValueTask DisposeAsync()
+    {
+        this._httpClient?.Dispose();
+        if (this._app != null)
+        {
+            await this._app.DisposeAsync();
+        }
+    }
+
+    [Fact]
+    public async Task MapFoundryResponses_NoUserAgentHeader_SetsAgentFrameworkUserAgentAsync()
+    {
+        // Arrange
+        await this.CreateTestServerAsync();
+
+        using var request = new HttpRequestMessage(HttpMethod.Get, "/test-ua");
+
+        // Act
+        var response = await this._httpClient!.SendAsync(request);
+        var userAgent = await response.Content.ReadAsStringAsync();
+
+        // Assert
+        Assert.Matches(VersionedUserAgentPattern, userAgent);
+    }
+
+    [Fact]
+    public async Task MapFoundryResponses_WithExistingUserAgent_AppendsAgentFrameworkUserAgentAsync()
+    {
+        // Arrange
+        await this.CreateTestServerAsync();
+
+        using var request = new HttpRequestMessage(HttpMethod.Get, "/test-ua");
+        request.Headers.TryAddWithoutValidation("User-Agent", "MyApp/1.0");
+
+        // Act
+        var response = await this._httpClient!.SendAsync(request);
+        var userAgent = await response.Content.ReadAsStringAsync();
+
+        // Assert
+        Assert.StartsWith("MyApp/1.0", userAgent);
+        Assert.Matches(VersionedUserAgentPattern, userAgent);
+    }
+
+    [Fact]
+    public async Task MapFoundryResponses_AlreadyContainsUserAgent_DoesNotDuplicateAsync()
+    {
+        // Arrange
+        await this.CreateTestServerAsync();
+
+        // First request to capture the actual middleware-generated value
+        using var firstRequest = new HttpRequestMessage(HttpMethod.Get, "/test-ua");
+        var firstResponse = await this._httpClient!.SendAsync(firstRequest);
+        var middlewareValue = await firstResponse.Content.ReadAsStringAsync();
+
+        // Act: send a second request that already contains the middleware value
+        using var secondRequest = new HttpRequestMessage(HttpMethod.Get, "/test-ua");
+        secondRequest.Headers.TryAddWithoutValidation("User-Agent", $"MyApp/2.0 {middlewareValue}");
+        var secondResponse = await this._httpClient!.SendAsync(secondRequest);
+        var userAgent = await secondResponse.Content.ReadAsStringAsync();
+
+        // Assert: should remain unchanged (no duplication)
+        Assert.Equal($"MyApp/2.0 {middlewareValue}", userAgent);
+        Assert.Single(VersionedUserAgentRegex().Matches(userAgent));
+    }
+
+    [Fact]
+    public async Task MapFoundryResponses_UserAgentValue_ContainsVersionAsync()
+    {
+        // Arrange
+        await this.CreateTestServerAsync();
+
+        using var request = new HttpRequestMessage(HttpMethod.Get, "/test-ua");
+
+        // Act
+        var response = await this._httpClient!.SendAsync(request);
+        var userAgent = await response.Content.ReadAsStringAsync();
+
+        // Assert: should match "agent-framework-dotnet/x.y.z" pattern
+        Assert.Matches(VersionedUserAgentPattern, userAgent);
+    }
+
+    private async Task CreateTestServerAsync()
+    {
+        var builder = WebApplication.CreateBuilder();
+        builder.WebHost.UseTestServer();
+
+        var mockAgent = new Mock<AIAgent>();
+        builder.Services.AddFoundryResponses(mockAgent.Object);
+
+        this._app = builder.Build();
+        this._app.MapFoundryResponses();
+
+        // Test endpoint that echoes the User-Agent header after middleware processing
+        this._app.MapGet("/test-ua", (HttpContext ctx) =>
+            Results.Text(ctx.Request.Headers.UserAgent.ToString()));
+
+        await this._app.StartAsync();
+
+        var testServer = this._app.Services.GetRequiredService<IServer>() as TestServer
+            ?? throw new InvalidOperationException("TestServer not found");
+
+        this._httpClient = testServer.CreateClient();
+    }
+
+    [GeneratedRegex(VersionedUserAgentPattern)]
+    private static partial Regex VersionedUserAgentRegex();
+}
diff --git a/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/Microsoft.Agents.AI.Foundry.UnitTests.csproj b/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/Microsoft.Agents.AI.Foundry.UnitTests.csproj
index 6473b799bf..f006096208 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/Microsoft.Agents.AI.Foundry.UnitTests.csproj
+++ b/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/Microsoft.Agents.AI.Foundry.UnitTests.csproj
@@ -12,6 +12,7 @@
 
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
     <PackageReference Include="Azure.AI.AgentServer.Responses" />
+    <PackageReference Include="Microsoft.AspNetCore.TestHost" />
   </ItemGroup>
 
   <!-- Hosting tests only compile on .NET Core TFMs -->