diff --git a/extension/pytree/function_ref.h b/extension/pytree/function_ref.h
index c81add169c8..aba9f87c2df 100644
--- a/extension/pytree/function_ref.h
+++ b/extension/pytree/function_ref.h
@@ -6,117 +6,19 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-//===- llvm/ADT/STLFunctionalExtras.h - Extras for <functional> -*- C++ -*-===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-//
-// This file contains some extension to <functional>.
-//
-// No library is required when using these functions.
-//
-//===----------------------------------------------------------------------===//
-//     Extra additions to <functional>
-//===----------------------------------------------------------------------===//
-
-/// An efficient, type-erasing, non-owning reference to a callable. This is
-/// intended for use as the type of a function parameter that is not used
-/// after the function in question returns.
-///
-/// This class does not own the callable, so it is not in general safe to store
-/// a FunctionRef.
-
-// torch::executor: modified from llvm::function_ref
-// - renamed to FunctionRef
-// - removed LLVM_GSL_POINTER and LLVM_LIFETIME_BOUND macro uses
-// - use namespaced internal::remove_cvref_t
-
 #pragma once
 
-#include <cstdint>
-#include <type_traits>
-#include <utility>
-
-namespace executorch {
-namespace extension {
-namespace pytree {
-
-//===----------------------------------------------------------------------===//
-//     Features from C++20
-//===----------------------------------------------------------------------===//
-
-namespace internal {
-
-template <typename T>
-struct remove_cvref {
-  using type =
-      typename std::remove_cv<typename std::remove_reference<T>::type>::type;
-};
-
-template <typename T>
-using remove_cvref_t = typename remove_cvref<T>::type;
-
-} // namespace internal
-
-template <typename Fn>
-class FunctionRef;
-
-template <typename Ret, typename... Params>
-class FunctionRef<Ret(Params...)> {
-  Ret (*callback)(intptr_t callable, Params... params) = nullptr;
-  intptr_t callable;
-
-  template <typename Callable>
-  static Ret callback_fn(intptr_t callable, Params... params) {
-    return (*reinterpret_cast<Callable*>(callable))(
-        std::forward<Params>(params)...);
-  }
-
- public:
-  FunctionRef() = default;
-  FunctionRef(std::nullptr_t) {}
-
-  template <typename Callable>
-  FunctionRef(
-      Callable&& callable,
-      // This is not the copy-constructor.
-      std::enable_if_t<!std::is_same<
-          internal::remove_cvref_t<Callable>,
-          FunctionRef>::value>* = nullptr,
-      // Functor must be callable and return a suitable type.
-      std::enable_if_t<
-          std::is_void<Ret>::value ||
-          std::is_convertible<
-              decltype(std::declval<Callable>()(std::declval<Params>()...)),
-              Ret>::value>* = nullptr)
-      : callback(callback_fn<std::remove_reference_t<Callable>>),
-        callable(reinterpret_cast<intptr_t>(&callable)) {}
-
-  Ret operator()(Params... params) const {
-    return callback(callable, std::forward<Params>(params)...);
-  }
+#include <executorch/runtime/core/function_ref.h>
 
-  explicit operator bool() const {
-    return callback;
-  }
+/// This header is DEPRECATED; use executorch/runtime/core/function_ref.h
+/// directly instead.
 
-  bool operator==(const FunctionRef<Ret(Params...)>& Other) const {
-    return callable == Other.callable;
-  }
-};
-} // namespace pytree
-} // namespace extension
-} // namespace executorch
+namespace executorch::extension::pytree {
+using executorch::runtime::FunctionRef;
+} // namespace executorch::extension::pytree
 
-namespace torch {
-namespace executor {
-namespace pytree {
+namespace torch::executor::pytree {
 // TODO(T197294990): Remove these deprecated aliases once all users have moved
 // to the new `::executorch` namespaces.
 using ::executorch::extension::pytree::FunctionRef;
-} // namespace pytree
-} // namespace executor
-} // namespace torch
+} // namespace torch::executor::pytree
diff --git a/extension/pytree/test/CMakeLists.txt b/extension/pytree/test/CMakeLists.txt
index 5d99bad1339..ce9b2cec6ec 100644
--- a/extension/pytree/test/CMakeLists.txt
+++ b/extension/pytree/test/CMakeLists.txt
@@ -19,6 +19,6 @@ set(EXECUTORCH_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/../../..)
 
 include(${EXECUTORCH_ROOT}/tools/cmake/Test.cmake)
 
-set(_test_srcs function_ref_test.cpp test_pytree.cpp)
+set(_test_srcs test_pytree.cpp)
 
 et_cxx_test(extension_pytree_test SOURCES ${_test_srcs} EXTRA_LIBS)
diff --git a/extension/pytree/test/TARGETS b/extension/pytree/test/TARGETS
index 190bdb0bc67..e49e8cd2791 100644
--- a/extension/pytree/test/TARGETS
+++ b/extension/pytree/test/TARGETS
@@ -10,12 +10,6 @@ cpp_unittest(
     deps = ["//executorch/extension/pytree:pytree"],
 )
 
-cpp_unittest(
-    name = "function_ref_test",
-    srcs = ["function_ref_test.cpp"],
-    deps = ["//executorch/extension/pytree:pytree"],
-)
-
 python_unittest(
     name = "pybindings_test",
     srcs = [
diff --git a/runtime/core/function_ref.h b/runtime/core/function_ref.h
new file mode 100644
index 00000000000..07d3d582b0c
--- /dev/null
+++ b/runtime/core/function_ref.h
@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+//===- llvm/ADT/STLFunctionalExtras.h - Extras for <functional> -*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains some extension to <functional>.
+//
+// No library is required when using these functions.
+//
+//===----------------------------------------------------------------------===//
+//     Extra additions to <functional>
+//===----------------------------------------------------------------------===//
+
+/// An efficient, type-erasing, non-owning reference to a callable. This is
+/// intended for use as the type of a function parameter that is not used
+/// after the function in question returns.
+///
+/// This class does not own the callable, so it is not in general safe to store
+/// a FunctionRef.
+
+// torch::executor: modified from llvm::function_ref
+// - renamed to FunctionRef
+// - removed LLVM_GSL_POINTER and LLVM_LIFETIME_BOUND macro uses
+// - use namespaced internal::remove_cvref_t
+
+#pragma once
+
+#include <cstdint>
+#include <type_traits>
+#include <utility>
+
+namespace executorch::runtime {
+
+//===----------------------------------------------------------------------===//
+//     Features from C++20
+//===----------------------------------------------------------------------===//
+
+namespace internal {
+
+template <typename T>
+struct remove_cvref {
+  using type =
+      typename std::remove_cv<typename std::remove_reference<T>::type>::type;
+};
+
+template <typename T>
+using remove_cvref_t = typename remove_cvref<T>::type;
+
+} // namespace internal
+
+template <typename Fn>
+class FunctionRef;
+
+template <typename Ret, typename... Params>
+class FunctionRef<Ret(Params...)> {
+  Ret (*callback)(intptr_t callable, Params... params) = nullptr;
+  intptr_t callable;
+
+  template <typename Callable>
+  static Ret callback_fn(intptr_t callable, Params... params) {
+    return (*reinterpret_cast<Callable*>(callable))(
+        std::forward<Params>(params)...);
+  }
+
+ public:
+  FunctionRef() = default;
+  FunctionRef(std::nullptr_t) {}
+
+  template <typename Callable>
+  FunctionRef(
+      Callable&& callable,
+      // This is not the copy-constructor.
+      std::enable_if_t<!std::is_same<
+          internal::remove_cvref_t<Callable>,
+          FunctionRef>::value>* = nullptr,
+      // Functor must be callable and return a suitable type.
+      std::enable_if_t<
+          std::is_void<Ret>::value ||
+          std::is_convertible<
+              decltype(std::declval<Callable>()(std::declval<Params>()...)),
+              Ret>::value>* = nullptr)
+      : callback(callback_fn<std::remove_reference_t<Callable>>),
+        callable(reinterpret_cast<intptr_t>(&callable)) {}
+
+  Ret operator()(Params... params) const {
+    return callback(callable, std::forward<Params>(params)...);
+  }
+
+  explicit operator bool() const {
+    return callback;
+  }
+
+  bool operator==(const FunctionRef<Ret(Params...)>& Other) const {
+    return callable == Other.callable;
+  }
+};
+} // namespace executorch::runtime
diff --git a/runtime/core/targets.bzl b/runtime/core/targets.bzl
index d3e02b1afb5..efc7853f3c1 100644
--- a/runtime/core/targets.bzl
+++ b/runtime/core/targets.bzl
@@ -41,6 +41,7 @@ def define_common_targets():
             "defines.h",
             "error.h",
             "freeable_buffer.h",
+            "function_ref.h",
             "result.h",
             "span.h",
         ],
diff --git a/runtime/core/test/CMakeLists.txt b/runtime/core/test/CMakeLists.txt
index 70f7cbf4bfd..bdc427baf7d 100644
--- a/runtime/core/test/CMakeLists.txt
+++ b/runtime/core/test/CMakeLists.txt
@@ -20,14 +20,15 @@ set(EXECUTORCH_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/../../..)
 include(${EXECUTORCH_ROOT}/tools/cmake/Test.cmake)
 
 set(_test_srcs
-    span_test.cpp
+    array_ref_test.cpp
     error_handling_test.cpp
+    evalue_test.cpp
     event_tracer_test.cpp
     freeable_buffer_test.cpp
-    array_ref_test.cpp
-    memory_allocator_test.cpp
+    function_ref_test.cpp
     hierarchical_allocator_test.cpp
-    evalue_test.cpp
+    memory_allocator_test.cpp
+    span_test.cpp
 )
 
 et_cxx_test(runtime_core_test SOURCES ${_test_srcs} EXTRA_LIBS)
diff --git a/extension/pytree/test/function_ref_test.cpp b/runtime/core/test/function_ref_test.cpp
similarity index 91%
rename from extension/pytree/test/function_ref_test.cpp
rename to runtime/core/test/function_ref_test.cpp
index cdb2c0538fd..beef00893cf 100644
--- a/extension/pytree/test/function_ref_test.cpp
+++ b/runtime/core/test/function_ref_test.cpp
@@ -6,13 +6,13 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-#include <executorch/extension/pytree/function_ref.h>
+#include <executorch/runtime/core/function_ref.h>
 
 #include <gtest/gtest.h>
 
 using namespace ::testing;
 
-using ::executorch::extension::pytree::FunctionRef;
+using ::executorch::runtime::FunctionRef;
 
 namespace {
 void one(int32_t& i) {
diff --git a/runtime/core/test/targets.bzl b/runtime/core/test/targets.bzl
index 7db74475c92..1ad0940c62e 100644
--- a/runtime/core/test/targets.bzl
+++ b/runtime/core/test/targets.bzl
@@ -33,6 +33,16 @@ def define_common_targets():
         ],
     )
 
+    runtime.cxx_test(
+        name = "function_ref_test",
+        srcs = [
+            "function_ref_test.cpp",
+        ],
+        deps = [
+            "//executorch/runtime/core:core",
+        ],
+    )
+    
     runtime.cxx_test(
         name = "event_tracer_test",
         srcs = [
diff --git a/test/utils/OSSTestConfig.json b/test/utils/OSSTestConfig.json
index be594f9d5f4..2cfc4b8a995 100644
--- a/test/utils/OSSTestConfig.json
+++ b/test/utils/OSSTestConfig.json
@@ -45,7 +45,6 @@
     {
         "directory": "extension/pytree/test",
         "sources": [
-            "function_ref_test.cpp",
             "test_pytree.cpp"
         ]
     },
@@ -96,14 +95,15 @@
     {
         "directory": "runtime/core/test",
         "sources": [
-            "span_test.cpp",
+            "array_ref_test.cpp",
             "error_handling_test.cpp",
+            "evalue_test.cpp",
             "event_tracer_test.cpp",
             "freeable_buffer_test.cpp",
-            "array_ref_test.cpp",
-            "memory_allocator_test.cpp",
+            "function_ref_test.cpp",
             "hierarchical_allocator_test.cpp",
-            "evalue_test.cpp"
+            "memory_allocator_test.cpp",
+            "span_test.cpp"
         ]
     },
     {