diff --git a/src/Agent.Plugins/GitSourceProvider.cs b/src/Agent.Plugins/GitSourceProvider.cs
index 3d1c871d17..a429ad9321 100644
--- a/src/Agent.Plugins/GitSourceProvider.cs
+++ b/src/Agent.Plugins/GitSourceProvider.cs
@@ -802,6 +802,24 @@ public async Task GetSourceAsync(
                     {
                         additionalCheckoutArgs.Add(args);
                     }
+
+                    // When using partial clones (fetch filters), set up authentication in git config
+                    // so that git's automatic promisor fetches can access credentials
+                    if (additionalFetchFilterOptions.Any())
+                    {
+                        string authHeader = GenerateAuthHeader(executionContext, username, password, useBearerAuthType);
+                        string configValue = $"AUTHORIZATION: {authHeader}";
+                        executionContext.Debug("Setting up git config authentication for partial clone promisor fetches.");
+                        int exitCode_configAuth = await gitCommandManager.GitConfig(executionContext, targetPath, configKey, configValue);
+                        if (exitCode_configAuth != 0)
+                        {
+                            executionContext.Warning($"Failed to set git config authentication for partial clone. Promisor fetches may fail. Exit code: {exitCode_configAuth}");
+                        }
+                        else
+                        {
+                            configModifications[configKey] = configValue;
+                        }
+                    }
                 }
                 else
                 {
diff --git a/src/Test/L0/Plugin/TestGitSourceProvider/GitSourceProviderL0.cs b/src/Test/L0/Plugin/TestGitSourceProvider/GitSourceProviderL0.cs
index 39e975550a..17b46a7283 100644
--- a/src/Test/L0/Plugin/TestGitSourceProvider/GitSourceProviderL0.cs
+++ b/src/Test/L0/Plugin/TestGitSourceProvider/GitSourceProviderL0.cs
@@ -6,6 +6,8 @@
 using Xunit;
 using System.IO;
 using System;
+using System.Linq;
+using System.Threading.Tasks;
 using Moq;
 using Agent.Plugins.Repository;
 using System.Collections.Generic;
@@ -112,6 +114,32 @@ public void TestSetWSICConnection()
         Assert.Contains("dev.azure.com/test/_git/myrepo", tc.TaskVariables.GetValueOrDefault("repoUrlWithCred").Value);
     }
 
+    [Fact]
+    [Trait("Level", "L0")]
+    [Trait("Category", "Plugin")]
+    public async Task TestPartialCloneAuthenticationConfigSetup()
+    {
+        using TestHostContext hc = new(this);
+        MockAgentTaskPluginExecutionContext tc = new(hc.GetTrace());
+        var gitCliManagerMock = new MockGitCliManager();
+        
+        // Arrange - simulate authenticated git source provider with partial clone (fetch filter)
+        tc.Inputs["fetchFilter"] = "blob:none";
+        tc.Variables.Add("UseFetchFilterInCheckoutTask", "true");
+        
+        var repositoryPath = Path.Combine(getWorkFolder(hc), "1", "testrepo");
+        
+        // Test the specific authentication config logic for partial clones
+        var gitSourceProvider = new TestAuthenticatedGitSourceProvider();
+        await gitSourceProvider.TestGitConfigForPartialClone(tc, gitCliManagerMock, repositoryPath, "test-user", "test-token", false);
+        
+        // Assert - verify that git config command was called with authentication header
+        var configCalls = gitCliManagerMock.GitCommandCallsOptions.FindAll(call => 
+            call.Contains("config") && call.Contains("http.extraheader") && call.Contains("AUTHORIZATION:"));
+        
+        Assert.True(configCalls.Count > 0, "Expected git config call with authentication header for partial clone, but none found");
+    }
+
     private Pipelines.RepositoryResource GetRepository(TestHostContext hostContext, String alias, String relativePath)
     {
         var workFolder = hostContext.GetDirectory(WellKnownDirectory.Work);
@@ -126,3 +154,28 @@ private Pipelines.RepositoryResource GetRepository(TestHostContext hostContext,
         return repo;
     }
 }
+
+// Test helper class to expose the relevant functionality for testing
+internal class TestAuthenticatedGitSourceProvider : AuthenticatedGitSourceProvider
+{
+    public override bool GitSupportsFetchingCommitBySha1Hash(GitCliManager gitCommandManager)
+    {
+        return true;
+    }
+
+    // Method to test the specific authentication config logic for partial clones
+    public async Task TestGitConfigForPartialClone(AgentTaskPluginExecutionContext executionContext, IGitCliManager gitCommandManager, string targetPath, string username, string password, bool useBearerAuthType)
+    {
+        // Simulate the condition where we have fetch filter options (partial clone)
+        var additionalFetchFilterOptions = new List<string> { "blob:none" };
+        
+        // Simulate the authentication setup logic for partial clones
+        if (additionalFetchFilterOptions.Any())
+        {
+            string authHeader = GenerateAuthHeader(executionContext, username, password, useBearerAuthType);
+            string configValue = $"AUTHORIZATION: {authHeader}";
+            executionContext.Debug("Setting up git config authentication for partial clone promisor fetches.");
+            await gitCommandManager.GitConfig(executionContext, targetPath, "http.extraheader", configValue);
+        }
+    }
+}
diff --git a/src/Test/L0/Plugin/TestGitSourceProvider/MockGitCliManager.cs b/src/Test/L0/Plugin/TestGitSourceProvider/MockGitCliManager.cs
index 78256742c0..4044d6e558 100644
--- a/src/Test/L0/Plugin/TestGitSourceProvider/MockGitCliManager.cs
+++ b/src/Test/L0/Plugin/TestGitSourceProvider/MockGitCliManager.cs
@@ -11,6 +11,7 @@ public class MockGitCliManager : GitCliManager
     {
         public List<string> GitCommandCallsOptions = new List<string>();
         public bool IsLfsConfigExistsing = false;
+        
         public override Task<Version> GitVersion(AgentTaskPluginExecutionContext context)
         {
             return Task.FromResult(new Version("2.30.2"));
@@ -21,6 +22,12 @@ public override Task<Version> GitLfsVersion(AgentTaskPluginExecutionContext cont
             return Task.FromResult(new Version("2.30.2"));
         }
 
+        public override Task<int> GitConfig(AgentTaskPluginExecutionContext context, string repositoryPath, string configKey, string configValue)
+        {
+            GitCommandCallsOptions.Add($"{repositoryPath},config,{configKey} {configValue},");
+            return Task.FromResult(0);
+        }
+
         protected override Task<int> ExecuteGitCommandAsync(AgentTaskPluginExecutionContext context, string repoRoot, string command, string options, IList<string> output)
         {
             return Task.FromResult(0);