diff --git a/src/Microsoft.Build.Tasks.Git.UnitTests/GitReferenceResolverTests.cs b/src/Microsoft.Build.Tasks.Git.UnitTests/GitReferenceResolverTests.cs
index c61fb555..bfdc6edb 100644
--- a/src/Microsoft.Build.Tasks.Git.UnitTests/GitReferenceResolverTests.cs
+++ b/src/Microsoft.Build.Tasks.Git.UnitTests/GitReferenceResolverTests.cs
@@ -40,6 +40,32 @@ public void ResolveReference()
             Assert.Null(resolver.ResolveReference("ref: refs/heads/none" + string.Join("/", Path.GetInvalidPathChars())));
         }
 
+        [Fact]
+        public void ResolveReference_SHA256()
+        {
+            using var temp = new TempRoot();
+
+            var gitDir = temp.CreateDirectory();
+
+            var commonDir = temp.CreateDirectory();
+            var refsHeadsDir = commonDir.CreateDirectory("refs").CreateDirectory("heads");
+
+            // SHA256 hash (64 characters)
+            refsHeadsDir.CreateFile("master").WriteAllText("0000000000000000000000000000000000000000000000000000000000000000");
+            refsHeadsDir.CreateFile("br1").WriteAllText("ref: refs/heads/br2");
+            refsHeadsDir.CreateFile("br2").WriteAllText("ref: refs/heads/master");
+
+            var resolver = new GitReferenceResolver(gitDir.Path, commonDir.Path);
+
+            // Verify SHA256 hash is accepted directly
+            Assert.Equal("0123456789ABCDEFabcdef000000000000000000000000000000000000000000", 
+                         resolver.ResolveReference("0123456789ABCDEFabcdef000000000000000000000000000000000000000000"));
+
+            Assert.Equal("0000000000000000000000000000000000000000000000000000000000000000", resolver.ResolveReference("ref: refs/heads/master"));
+            Assert.Equal("0000000000000000000000000000000000000000000000000000000000000000", resolver.ResolveReference("ref: refs/heads/br1"));
+            Assert.Equal("0000000000000000000000000000000000000000000000000000000000000000", resolver.ResolveReference("ref: refs/heads/br2"));
+        }
+
         [Fact]
         public void ResolveReference_Errors()
         {
@@ -59,8 +85,12 @@ public void ResolveReference_Errors()
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference("ref: xyz/heads/rec1"));
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference("ref:refs/heads/rec1"));
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference("refs/heads/rec1"));
+            // Invalid SHA1 hash lengths
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference(new string('0', 39)));
             Assert.Throws<InvalidDataException>(() => resolver.ResolveReference(new string('0', 41)));
+            // Invalid SHA256 hash lengths
+            Assert.Throws<InvalidDataException>(() => resolver.ResolveReference(new string('0', 63)));
+            Assert.Throws<InvalidDataException>(() => resolver.ResolveReference(new string('0', 65)));
         }
 
         [Fact]
@@ -87,6 +117,31 @@ 2222222222222222222222222222222222222222 refs/heads/br2
             Assert.Equal("2222222222222222222222222222222222222222", resolver.ResolveReference("ref: refs/heads/br2"));
         }
 
+        [Fact]
+        public void ResolveReference_Packed_SHA256()
+        {
+            using var temp = new TempRoot();
+
+            var gitDir = temp.CreateDirectory();
+
+            // Packed refs with SHA256 hashes (64 characters)
+            gitDir.CreateFile("packed-refs").WriteAllText(
+@"# pack-refs with: peeled fully-peeled sorted
+1111111111111111111111111111111111111111111111111111111111111111 refs/heads/master
+2222222222222222222222222222222222222222222222222222222222222222 refs/heads/br2
+");
+            var commonDir = temp.CreateDirectory();
+            var refsHeadsDir = commonDir.CreateDirectory("refs").CreateDirectory("heads");
+
+            refsHeadsDir.CreateFile("br1").WriteAllText("ref: refs/heads/br2");
+
+            var resolver = new GitReferenceResolver(gitDir.Path, commonDir.Path);
+
+            Assert.Equal("1111111111111111111111111111111111111111111111111111111111111111", resolver.ResolveReference("ref: refs/heads/master"));
+            Assert.Equal("2222222222222222222222222222222222222222222222222222222222222222", resolver.ResolveReference("ref: refs/heads/br1"));
+            Assert.Equal("2222222222222222222222222222222222222222222222222222222222222222", resolver.ResolveReference("ref: refs/heads/br2"));
+        }
+
         [Fact]
         public void ReadPackedReferences()
         {
@@ -110,6 +165,29 @@ 7777777777777777777777777777777777777777 refs/heads/br
             }, actual.Select(e => $"{e.Key}:{e.Value}"));
         }
 
+        [Fact]
+        public void ReadPackedReferences_SHA256()
+        {
+            var packedRefs =
+@"# pack-refs with:
+1111111111111111111111111111111111111111111111111111111111111111 refs/heads/master
+2222222222222222222222222222222222222222222222222222222222222222 refs/heads/br
+^3333333333333333333333333333333333333333333333333333333333333333
+4444444444444444444444444444444444444444444444444444444444444444 x
+5555555555555555555555555555555555555555555555555555555555555555 y 
+6666666666666666666666666666666666666666666666666666666666666666 y z
+7777777777777777777777777777777777777777777777777777777777777777 refs/heads/br
+";
+
+            var actual = GitReferenceResolver.ReadPackedReferences(new StringReader(packedRefs), "<path>");
+
+            AssertEx.SetEqual(new[]
+            {
+                "refs/heads/br:2222222222222222222222222222222222222222222222222222222222222222",
+                "refs/heads/master:1111111111111111111111111111111111111111111111111111111111111111"
+            }, actual.Select(e => $"{e.Key}:{e.Value}"));
+        }
+
         [Theory]
         [InlineData("# pack-refs with:")]
         [InlineData("# pack-refs with:xyz")]
diff --git a/src/Microsoft.Build.Tasks.Git.UnitTests/GitRepositoryTests.cs b/src/Microsoft.Build.Tasks.Git.UnitTests/GitRepositoryTests.cs
index 7ba9993d..7cc4eb83 100644
--- a/src/Microsoft.Build.Tasks.Git.UnitTests/GitRepositoryTests.cs
+++ b/src/Microsoft.Build.Tasks.Git.UnitTests/GitRepositoryTests.cs
@@ -226,6 +226,7 @@ public void OpenRepository_Version1_Extensions()
     preciousObjects = true
     partialClone = promisor_remote
     worktreeConfig = true
+    objectformat = sha256
 ");
 
             Assert.True(GitRepository.TryFindRepository(gitDir.Path, out var location));
@@ -264,6 +265,36 @@ public void OpenRepository_Version1_UnknownExtension()
             Assert.Throws<NotSupportedException>(() => GitRepository.OpenRepository(src.Path, new GitEnvironment(homeDir.Path)));
         }
 
+        [Fact]
+        public void OpenRepository_Version1_ObjectFormatExtension()
+        {
+            using var temp = new TempRoot();
+
+            var homeDir = temp.CreateDirectory();
+
+            var workingDir = temp.CreateDirectory();
+            var gitDir = workingDir.CreateDirectory(".git");
+
+            gitDir.CreateFile("HEAD").WriteAllText("ref: refs/heads/master");
+            gitDir.CreateDirectory("refs").CreateDirectory("heads").CreateFile("master").WriteAllText("0000000000000000000000000000000000000000");
+            gitDir.CreateDirectory("objects");
+
+            gitDir.CreateFile("config").WriteAllText(@"
+[core]
+	repositoryformatversion = 1
+[extensions]
+	objectformat = sha256");
+
+            var src = workingDir.CreateDirectory("src");
+
+            // Should not throw - objectformat extension should be supported
+            var repository = GitRepository.OpenRepository(src.Path, new GitEnvironment(homeDir.Path));
+            Assert.NotNull(repository);
+            Assert.Equal(gitDir.Path, repository.GitDirectory);
+            Assert.Equal(gitDir.Path, repository.CommonDirectory);
+            Assert.Equal(workingDir.Path, repository.WorkingDirectory);
+        }
+
         [Fact]
         public void OpenRepository_VersionNotSupported()
         {
diff --git a/src/Microsoft.Build.Tasks.Git/GitDataReader/GitReferenceResolver.cs b/src/Microsoft.Build.Tasks.Git/GitDataReader/GitReferenceResolver.cs
index 7d970c09..54d6fb1c 100644
--- a/src/Microsoft.Build.Tasks.Git/GitDataReader/GitReferenceResolver.cs
+++ b/src/Microsoft.Build.Tasks.Git/GitDataReader/GitReferenceResolver.cs
@@ -254,7 +254,8 @@ internal static string ReadReferenceFromFile(string path)
         private string? ResolvePackedReference(string reference)
             => _lazyPackedReferences.Value.TryGetValue(reference, out var objectId) ? objectId : null;
 
+        // SHA1 hashes are 40 hex characters, SHA256 hashes are 64 hex characters
         private static bool IsObjectId(string reference)
-            => reference.Length == 40 && reference.All(CharUtils.IsHexadecimalDigit);
+            => (reference.Length == 40 || reference.Length == 64) && reference.All(CharUtils.IsHexadecimalDigit);
     }
 }
diff --git a/src/Microsoft.Build.Tasks.Git/GitDataReader/GitRepository.cs b/src/Microsoft.Build.Tasks.Git/GitDataReader/GitRepository.cs
index fc7446ea..7186b258 100644
--- a/src/Microsoft.Build.Tasks.Git/GitDataReader/GitRepository.cs
+++ b/src/Microsoft.Build.Tasks.Git/GitDataReader/GitRepository.cs
@@ -25,7 +25,7 @@ internal sealed class GitRepository
         private const string GitModulesFileName = ".gitmodules";
 
         private static readonly ImmutableArray<string> s_knownExtensions =
-            ImmutableArray.Create("noop", "preciousObjects", "partialclone", "worktreeConfig");
+            ImmutableArray.Create("noop", "preciousObjects", "partialclone", "worktreeConfig", "objectformat");
 
         public GitConfig Config { get; }