diff --git a/FirebaseCore/Internal/Sources/Utilities/AtomicBox.swift b/FirebaseCore/Internal/Sources/Utilities/AtomicBox.swift
deleted file mode 100644
index 6346d05701c..00000000000
--- a/FirebaseCore/Internal/Sources/Utilities/AtomicBox.swift
+++ /dev/null
@@ -1,45 +0,0 @@
-// Copyright 2025 Google LLC
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//      http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-import Foundation
-
-final class AtomicBox<T> {
-  private var _value: T
-  private let lock = NSLock()
-
-  public init(_ value: T) {
-    _value = value
-  }
-
-  public func value() -> T {
-    lock.withLock {
-      _value
-    }
-  }
-
-  @discardableResult
-  public func withLock(_ mutatingBody: (_ value: inout T) -> Void) -> T {
-    lock.withLock {
-      mutatingBody(&_value)
-      return _value
-    }
-  }
-
-  @discardableResult
-  public func withLock<R>(_ mutatingBody: (_ value: inout T) throws -> R) rethrows -> R {
-    try lock.withLock {
-      try mutatingBody(&_value)
-    }
-  }
-}
diff --git a/FirebaseFunctions/Sources/Functions.swift b/FirebaseFunctions/Sources/Functions.swift
index a87c68324a8..8ab6d63e780 100644
--- a/FirebaseFunctions/Sources/Functions.swift
+++ b/FirebaseFunctions/Sources/Functions.swift
@@ -25,36 +25,7 @@ import Foundation
 #endif
 
 internal import FirebaseCoreExtension
-
-final class AtomicBox<T>: Sendable {
-  private nonisolated(unsafe) var _value: T
-  private let lock = NSLock()
-
-  public init(_ value: T) where T: Sendable {
-    _value = value
-  }
-
-  public func value() -> T {
-    lock.withLock {
-      _value
-    }
-  }
-
-  @discardableResult
-  public func withLock(_ mutatingBody: (_ value: inout T) -> Void) -> T {
-    lock.withLock {
-      mutatingBody(&_value)
-      return _value
-    }
-  }
-
-  @discardableResult
-  public func withLock<R>(_ mutatingBody: (_ value: inout T) throws -> R) rethrows -> R {
-    try lock.withLock {
-      try mutatingBody(&_value)
-    }
-  }
-}
+private import FirebaseCoreInternal
 
 /// File specific constants.
 private enum Constants {
@@ -82,8 +53,7 @@ enum FunctionsConstants {
 
   /// A map of active instances, grouped by app. Keys are FirebaseApp names and values are arrays
   /// containing all instances of Functions associated with the given app.
-  private static let instances: AtomicBox<[String: [Functions]]> =
-    AtomicBox([:])
+  private static let instances = FIRAllocatedUnfairLock<[String: [Functions]]>(initialState: [:])
 
   /// The custom domain to use for all functions references (optional).
   let customDomain: String?
@@ -91,7 +61,7 @@ enum FunctionsConstants {
   /// The region to use for all function references.
   let region: String
 
-  private let _emulatorOrigin: AtomicBox<String?>
+  private let _emulatorOrigin: FIRAllocatedUnfairLock<String?>
 
   // MARK: - Public APIs
 
@@ -371,7 +341,7 @@ enum FunctionsConstants {
     self.projectID = projectID
     self.region = region
     self.customDomain = customDomain
-    _emulatorOrigin = AtomicBox(nil)
+    _emulatorOrigin = FIRAllocatedUnfairLock(initialState: nil)
     contextProvider = FunctionsContextProvider(auth: auth,
                                                messaging: messaging,
                                                appCheck: appCheck)
diff --git a/FirebaseFunctions/Sources/HTTPSCallable.swift b/FirebaseFunctions/Sources/HTTPSCallable.swift
index b1d00830576..ab839003e17 100644
--- a/FirebaseFunctions/Sources/HTTPSCallable.swift
+++ b/FirebaseFunctions/Sources/HTTPSCallable.swift
@@ -14,6 +14,8 @@
 
 import Foundation
 
+private import FirebaseCoreInternal
+
 /// A `HTTPSCallableResult` contains the result of calling a `HTTPSCallable`.
 @objc(FIRHTTPSCallableResult)
 open class HTTPSCallableResult: NSObject {
@@ -163,7 +165,7 @@ private extension HTTPSCallable {
 
     // MARK: - Public Properties
 
-    let _timeoutInterval: AtomicBox<TimeInterval> = .init(70)
+    let _timeoutInterval = FIRAllocatedUnfairLock<TimeInterval>(initialState: 70)
 
     /// The timeout to use when calling the function. Defaults to 70 seconds.
     var timeoutInterval: TimeInterval {
diff --git a/FirebaseSessions/Sources/Public/SessionsDependencies.swift b/FirebaseSessions/Sources/Public/SessionsDependencies.swift
index e929fff98d4..9e0b3aafe6e 100644
--- a/FirebaseSessions/Sources/Public/SessionsDependencies.swift
+++ b/FirebaseSessions/Sources/Public/SessionsDependencies.swift
@@ -15,27 +15,7 @@
 
 import Foundation
 
-private final class AtomicBox<T> {
-  private var _value: T
-  private let lock = NSLock()
-
-  init(_ value: T) {
-    _value = value
-  }
-
-  func value() -> T {
-    lock.withLock {
-      _value
-    }
-  }
-
-  @discardableResult func withLock(_ body: (_ value: inout T) -> Void) -> T {
-    lock.withLock {
-      body(&_value)
-      return _value
-    }
-  }
-}
+private import FirebaseCoreInternal
 
 /// Sessions Dependencies determines when a dependent SDK is
 /// installed in the app. The Sessions SDK uses this to figure
@@ -46,10 +26,8 @@ private final class AtomicBox<T> {
 /// dependent SDKs
 @objc(FIRSessionsDependencies)
 public class SessionsDependencies: NSObject {
-  private nonisolated(unsafe) static let _dependencies: AtomicBox<Set<SessionsSubscriberName>> =
-    AtomicBox(
-      Set()
-    )
+  private static let _dependencies =
+    FIRAllocatedUnfairLock<Set<SessionsSubscriberName>>(initialState: Set())
 
   static var dependencies: Set<SessionsSubscriberName> {
     _dependencies.value()