diff --git a/src/Microsoft.DotNet.Helix/Client/CSharp/ApiFactory.cs b/src/Microsoft.DotNet.Helix/Client/CSharp/ApiFactory.cs
index f5f6f7cec00..427101e2cef 100644
--- a/src/Microsoft.DotNet.Helix/Client/CSharp/ApiFactory.cs
+++ b/src/Microsoft.DotNet.Helix/Client/CSharp/ApiFactory.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using Azure.Core;
 
 namespace Microsoft.DotNet.Helix.Client
 {
@@ -20,6 +21,15 @@ public static IHelixApi GetAuthenticated(string accessToken)
             return new HelixApi(new HelixApiOptions(new HelixApiTokenCredential(accessToken)));
         }
 
+        /// <summary>
+        /// Obtains an API client using an Entra credential for authenticated access to internal queues.
+        /// The client requests the production Helix API scope and refreshes tokens based on their expiry.
+        /// </summary>
+        public static IHelixApi GetAuthenticatedWithEntra(TokenCredential credential)
+        {
+            return new HelixApi(new HelixApiOptions(ValidateEntraCredential(credential)));
+        }
+
         /// <summary>
         /// Obtains API client for unauthenticated access to external queues.
         /// The client will access production Helix instance.
@@ -46,6 +56,29 @@ public static IHelixApi GetAuthenticated(string baseUri, string accessToken)
             return new HelixApi(new HelixApiOptions(new Uri(baseUri), new HelixApiTokenCredential(accessToken)));
         }
 
+        /// <summary>
+        /// Obtains an API client using an Entra credential for authenticated access to the provided Helix instance.
+        /// Production and staging scopes are selected from the base URI.
+        /// </summary>
+        public static IHelixApi GetAuthenticatedWithEntra(string baseUri, TokenCredential credential)
+        {
+            return new HelixApi(new HelixApiOptions(new Uri(baseUri), ValidateEntraCredential(credential)));
+        }
+
+        /// <summary>
+        /// Obtains an API client using an Entra credential and explicit scope for a custom Helix instance.
+        /// </summary>
+        public static IHelixApi GetAuthenticatedWithEntra(
+            string baseUri,
+            TokenCredential credential,
+            string scope)
+        {
+            return new HelixApi(new HelixApiOptions(
+                new Uri(baseUri),
+                ValidateEntraCredential(credential),
+                new[] { scope }));
+        }
+
         /// <summary>
         /// Obtains API client for unauthenticated access to external queues.
         /// The client will access Helix instance at the provided URI.
@@ -58,5 +91,22 @@ public static IHelixApi GetAnonymous(string baseUri)
         {
             return new HelixApi(new HelixApiOptions(new Uri(baseUri)));
         }
+
+        private static TokenCredential ValidateEntraCredential(TokenCredential credential)
+        {
+            if (credential == null)
+            {
+                throw new ArgumentNullException(nameof(credential));
+            }
+
+            if (credential is HelixApiTokenCredential)
+            {
+                throw new ArgumentException(
+                    "HelixApiTokenCredential represents a PAT. Use GetAuthenticated(...) for PAT authentication.",
+                    nameof(credential));
+            }
+
+            return credential;
+        }
     }
 }
diff --git a/src/Microsoft.DotNet.Helix/Client/CSharp/HelixApiOptions.cs b/src/Microsoft.DotNet.Helix/Client/CSharp/HelixApiOptions.cs
index e525ec33435..9e44c61994b 100644
--- a/src/Microsoft.DotNet.Helix/Client/CSharp/HelixApiOptions.cs
+++ b/src/Microsoft.DotNet.Helix/Client/CSharp/HelixApiOptions.cs
@@ -2,26 +2,118 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using Azure.Core;
+using Azure.Core.Pipeline;
 using System;
+using System.Collections.Generic;
+using System.Linq;
 
 namespace Microsoft.DotNet.Helix.Client
 {
+    public enum HelixApiAuthenticationMode
+    {
+        Anonymous,
+        PersonalAccessToken,
+        EntraId,
+    }
+
     partial class HelixApiOptions
     {
+        public const string ProductionScope = "api://eb70c40b-c265-44f7-842e-1a568f035f33/.default";
+        public const string StagingScope = "api://f45b17a4-149b-4f89-91bc-e6331af8d0e8/.default";
+
         // See https://github.com/Azure/azure-sdk-for-net/blob/master/sdk/core/Azure.Core/src/RetryOptions.cs for values this overrides
         public const int DefaultRetryDelaySeconds = 10;
         public const int DefaultMaxRetryCount = 5;
 
+        public HelixApiOptions(Uri baseUri, TokenCredential credentials, IEnumerable<string> scopes)
+        {
+            BaseUri = ValidateBaseUri(baseUri);
+            Credentials = credentials ?? throw new ArgumentNullException(nameof(credentials));
+            if (credentials is HelixApiTokenCredential)
+            {
+                throw new ArgumentException(
+                    "Explicit scopes are only supported for Entra credentials. " +
+                    "For PAT authentication, pass HelixApiTokenCredential without explicit scopes.",
+                    nameof(credentials));
+            }
+
+            string[] tokenScopes = scopes?.ToArray() ?? throw new ArgumentNullException(nameof(scopes));
+            if (tokenScopes.Length == 0 || tokenScopes.Any(string.IsNullOrWhiteSpace))
+            {
+                throw new ArgumentException("At least one non-empty token scope is required.", nameof(scopes));
+            }
+            TokenScopes = Array.AsReadOnly(tokenScopes);
+
+            InitializeOptions();
+        }
+
+        public HelixApiAuthenticationMode AuthenticationMode { get; private set; }
+
+        public IReadOnlyList<string> TokenScopes { get; private set; } = Array.Empty<string>();
+
         partial void InitializeOptions()
         {
-            if (Credentials != null)
+            if (Credentials == null)
             {
+                AuthenticationMode = HelixApiAuthenticationMode.Anonymous;
+            }
+            else if (Credentials is HelixApiTokenCredential)
+            {
+                AuthenticationMode = HelixApiAuthenticationMode.PersonalAccessToken;
+                TokenScopes = Array.Empty<string>();
                 AddPolicy(new HelixApiTokenAuthenticationPolicy(Credentials), HttpPipelinePosition.PerCall);
             }
+            else
+            {
+                AuthenticationMode = HelixApiAuthenticationMode.EntraId;
+                if (TokenScopes.Count == 0)
+                {
+                    TokenScopes = Array.AsReadOnly(new[] { GetDefaultScope(BaseUri) });
+                }
+
+                AddPolicy(
+                    new BearerTokenAuthenticationPolicy(Credentials, TokenScopes.ToArray()),
+                    HttpPipelinePosition.PerRetry);
+            }
 
             // Users should not generally need to modify these but can do so after creating a HelixApi object if needed
             Retry.Delay = TimeSpan.FromSeconds(DefaultRetryDelaySeconds);
             Retry.MaxRetries = DefaultMaxRetryCount;
         }
+
+        private static string GetDefaultScope(Uri baseUri)
+        {
+            baseUri = ValidateBaseUri(baseUri);
+
+            if (baseUri.Host.Equals("helix.dot.net", StringComparison.OrdinalIgnoreCase))
+            {
+                return ProductionScope;
+            }
+
+            if (baseUri.Host.Equals("helix.int-dot.net", StringComparison.OrdinalIgnoreCase))
+            {
+                return StagingScope;
+            }
+
+            throw new ArgumentException(
+                $"No default Entra scope is known for Helix API host '{baseUri.Host}'. " +
+                "Use the HelixApiOptions constructor that accepts explicit scopes.",
+                nameof(baseUri));
+        }
+
+        private static Uri ValidateBaseUri(Uri baseUri)
+        {
+            if (baseUri == null)
+            {
+                throw new ArgumentNullException(nameof(baseUri));
+            }
+
+            if (!baseUri.IsAbsoluteUri)
+            {
+                throw new ArgumentException("The Helix API base URI must be absolute.", nameof(baseUri));
+            }
+
+            return baseUri;
+        }
     }
 }
diff --git a/src/Microsoft.DotNet.Helix/Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests/HelixApiAuthenticationTests.cs b/src/Microsoft.DotNet.Helix/Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests/HelixApiAuthenticationTests.cs
new file mode 100644
index 00000000000..8772bb4b519
--- /dev/null
+++ b/src/Microsoft.DotNet.Helix/Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests/HelixApiAuthenticationTests.cs
@@ -0,0 +1,182 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Azure.Core;
+using Microsoft.DotNet.Helix.Client;
+using Xunit;
+
+namespace Microsoft.DotNet.Helix.Sdk.Tests
+{
+    public class HelixApiAuthenticationTests
+    {
+        [Fact]
+        public void AnonymousOptionsExposeAnonymousMode()
+        {
+            var options = new HelixApiOptions();
+
+            Assert.Equal(HelixApiAuthenticationMode.Anonymous, options.AuthenticationMode);
+            Assert.Empty(options.TokenScopes);
+        }
+
+        [Fact]
+        public void PatCredentialPreservesLegacyAuthenticationMode()
+        {
+            var options = new HelixApiOptions(new HelixApiTokenCredential("legacy-token"));
+
+            Assert.Equal(HelixApiAuthenticationMode.PersonalAccessToken, options.AuthenticationMode);
+            Assert.Empty(options.TokenScopes);
+        }
+
+        [Fact]
+        public void ProductionCredentialUsesProductionScope()
+        {
+            var options = new HelixApiOptions(new TestTokenCredential());
+
+            Assert.Equal(HelixApiAuthenticationMode.EntraId, options.AuthenticationMode);
+            Assert.Equal(new[] { HelixApiOptions.ProductionScope }, options.TokenScopes);
+        }
+
+        [Fact]
+        public void StagingCredentialUsesStagingScope()
+        {
+            var options = new HelixApiOptions(
+                new Uri("https://helix.int-dot.net/"),
+                new TestTokenCredential());
+
+            Assert.Equal(HelixApiAuthenticationMode.EntraId, options.AuthenticationMode);
+            Assert.Equal(new[] { HelixApiOptions.StagingScope }, options.TokenScopes);
+        }
+
+        [Fact]
+        public void CustomHostRequiresExplicitScope()
+        {
+            var exception = Assert.Throws<ArgumentException>(() =>
+                new HelixApiOptions(new Uri("https://localhost:5001/"), new TestTokenCredential()));
+
+            Assert.Contains("explicit scopes", exception.Message);
+        }
+
+        [Fact]
+        public void EntraCredentialRequiresBaseUri()
+        {
+            Assert.Throws<ArgumentNullException>(() =>
+                new HelixApiOptions(null, new TestTokenCredential()));
+        }
+
+        [Fact]
+        public void EntraCredentialRequiresAbsoluteBaseUri()
+        {
+            Assert.Throws<ArgumentException>(() =>
+                new HelixApiOptions(new Uri("relative", UriKind.Relative), new TestTokenCredential()));
+        }
+
+        [Fact]
+        public void CustomHostUsesExplicitScope()
+        {
+            const string scope = "api://custom-helix/.default";
+            var options = new HelixApiOptions(
+                new Uri("https://localhost:5001/"),
+                new TestTokenCredential(),
+                new[] { scope });
+
+            Assert.Equal(HelixApiAuthenticationMode.EntraId, options.AuthenticationMode);
+            Assert.Equal(new[] { scope }, options.TokenScopes);
+        }
+
+        [Fact]
+        public void ExplicitScopeCannotBeEmpty()
+        {
+            Assert.Throws<ArgumentException>(() =>
+                new HelixApiOptions(
+                    new Uri("https://localhost:5001/"),
+                    new TestTokenCredential(),
+                    new[] { "" }));
+        }
+
+        [Fact]
+        public void ExplicitScopeRequiresAbsoluteBaseUri()
+        {
+            Assert.Throws<ArgumentException>(() =>
+                new HelixApiOptions(
+                    new Uri("relative", UriKind.Relative),
+                    new TestTokenCredential(),
+                    new[] { "api://custom-helix/.default" }));
+        }
+
+        [Fact]
+        public void ExplicitScopeRejectsPatCredential()
+        {
+            var exception = Assert.Throws<ArgumentException>(() =>
+                new HelixApiOptions(
+                    new Uri("https://localhost:5001/"),
+                    new HelixApiTokenCredential("legacy-token"),
+                    new[] { "api://custom-helix/.default" }));
+
+            Assert.Contains("without explicit scopes", exception.Message);
+        }
+
+        [Fact]
+        public void EntraFactoryUsesProductionScope()
+        {
+            var api = Assert.IsType<HelixApi>(
+                ApiFactory.GetAuthenticatedWithEntra(new TestTokenCredential()));
+
+            Assert.Equal(HelixApiAuthenticationMode.EntraId, api.Options.AuthenticationMode);
+            Assert.Equal(new[] { HelixApiOptions.ProductionScope }, api.Options.TokenScopes);
+        }
+
+        [Fact]
+        public void EntraFactoryRequiresCredential()
+        {
+            Assert.Throws<ArgumentNullException>(() =>
+                ApiFactory.GetAuthenticatedWithEntra(null));
+            Assert.Throws<ArgumentNullException>(() =>
+                ApiFactory.GetAuthenticatedWithEntra("https://helix.dot.net/", null));
+            Assert.Throws<ArgumentNullException>(() =>
+                ApiFactory.GetAuthenticatedWithEntra(
+                    "https://localhost:5001/",
+                    null,
+                    "api://custom-helix/.default"));
+        }
+
+        [Fact]
+        public void EntraFactoryRejectsPatCredential()
+        {
+            var credential = new HelixApiTokenCredential("legacy-token");
+
+            var productionException = Assert.Throws<ArgumentException>(() =>
+                ApiFactory.GetAuthenticatedWithEntra(credential));
+            var hostException = Assert.Throws<ArgumentException>(() =>
+                ApiFactory.GetAuthenticatedWithEntra("https://helix.dot.net/", credential));
+            var explicitScopeException = Assert.Throws<ArgumentException>(() =>
+                ApiFactory.GetAuthenticatedWithEntra(
+                    "https://localhost:5001/",
+                    credential,
+                    "api://custom-helix/.default"));
+
+            Assert.Contains("GetAuthenticated", productionException.Message);
+            Assert.Contains("GetAuthenticated", hostException.Message);
+            Assert.Contains("GetAuthenticated", explicitScopeException.Message);
+        }
+
+        private sealed class TestTokenCredential : TokenCredential
+        {
+            public override AccessToken GetToken(
+                TokenRequestContext requestContext,
+                CancellationToken cancellationToken)
+            {
+                return new AccessToken("test-token", DateTimeOffset.UtcNow.AddMinutes(30));
+            }
+
+            public override ValueTask<AccessToken> GetTokenAsync(
+                TokenRequestContext requestContext,
+                CancellationToken cancellationToken)
+            {
+                return new ValueTask<AccessToken>(GetToken(requestContext, cancellationToken));
+            }
+        }
+    }
+}
diff --git a/src/Microsoft.DotNet.Helix/Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests.csproj b/src/Microsoft.DotNet.Helix/Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests.csproj
index c464b912e7d..2038e551ea9 100644
--- a/src/Microsoft.DotNet.Helix/Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests.csproj
+++ b/src/Microsoft.DotNet.Helix/Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests.csproj
@@ -21,6 +21,7 @@
     <ProjectReference Include="..\..\..\Common\Microsoft.Arcade.Common\Microsoft.Arcade.Common.csproj" />
     <ProjectReference Include="..\..\..\Common\Microsoft.Arcade.Test.Common\Microsoft.Arcade.Test.Common.csproj" />
     <ProjectReference Include="..\..\..\Microsoft.DotNet.Internal.DependencyInjection.Testing\Microsoft.DotNet.Internal.DependencyInjection.Testing.csproj" />
+    <ProjectReference Include="..\..\Client\CSharp\Microsoft.DotNet.Helix.Client.csproj" />
     <ProjectReference Include="..\..\Sdk\Microsoft.DotNet.Helix.Sdk.csproj" />
     <ProjectReference Include="..\..\JobMonitor\Microsoft.DotNet.Helix.JobMonitor.csproj" />
   </ItemGroup>