diff --git a/FirebaseAuth/Sources/Swift/ActionCode/ActionCodeSettings.swift b/FirebaseAuth/Sources/Swift/ActionCode/ActionCodeSettings.swift
index 17bd7a30433..74472e33c71 100644
--- a/FirebaseAuth/Sources/Swift/ActionCode/ActionCodeSettings.swift
+++ b/FirebaseAuth/Sources/Swift/ActionCode/ActionCodeSettings.swift
@@ -105,22 +105,22 @@ import Foundation
 private extension ActionCodeSettings {
   /// Checked Sendable implementation of `ActionCodeSettings`.
   final class SendableActionCodeSettings: Sendable {
-    let url = FIRAllocatedUnfairLock<URL?>(initialState: nil)
+    let url = UnfairLock<URL?>(nil)
 
-    let handleCodeInApp = FIRAllocatedUnfairLock<Bool>(initialState: false)
+    let handleCodeInApp = UnfairLock<Bool>(false)
 
-    let iOSBundleID: FIRAllocatedUnfairLock<String?>
+    let iOSBundleID: UnfairLock<String?>
 
-    let androidPackageName = FIRAllocatedUnfairLock<String?>(initialState: nil)
+    let androidPackageName = UnfairLock<String?>(nil)
 
-    let androidMinimumVersion = FIRAllocatedUnfairLock<String?>(initialState: nil)
+    let androidMinimumVersion = UnfairLock<String?>(nil)
 
-    let androidInstallIfNotAvailable = FIRAllocatedUnfairLock<Bool>(initialState: false)
+    let androidInstallIfNotAvailable = UnfairLock<Bool>(false)
 
-    let linkDomain = FIRAllocatedUnfairLock<String?>(initialState: nil)
+    let linkDomain = UnfairLock<String?>(nil)
 
     init() {
-      iOSBundleID = FIRAllocatedUnfairLock<String?>(initialState: Bundle.main.bundleIdentifier)
+      iOSBundleID = UnfairLock<String?>(Bundle.main.bundleIdentifier)
     }
 
     func setAndroidPackageName(_ androidPackageName: String,
diff --git a/FirebaseAuth/Sources/Swift/Storage/AuthKeychainServices.swift b/FirebaseAuth/Sources/Swift/Storage/AuthKeychainServices.swift
index 349da7b73f8..fb3004da268 100644
--- a/FirebaseAuth/Sources/Swift/Storage/AuthKeychainServices.swift
+++ b/FirebaseAuth/Sources/Swift/Storage/AuthKeychainServices.swift
@@ -102,7 +102,7 @@ final class AuthKeychainServices: Sendable {
   /// been deleted.
   ///
   /// This dictionary is to avoid unnecessary keychain operations against legacy items.
-  private let legacyEntryDeletedForKey = FIRAllocatedUnfairLock<Set<String>>(initialState: [])
+  private let legacyEntryDeletedForKey = UnfairLock<Set<String>>([])
 
   func data(forKey key: String) throws -> Data? {
     if let data = try getItemLegacy(query: genericPasswordQuery(key: key)) {
diff --git a/FirebaseAuth/Sources/Swift/SystemService/SecureTokenService.swift b/FirebaseAuth/Sources/Swift/SystemService/SecureTokenService.swift
index 34f52a60a28..223f06e8014 100644
--- a/FirebaseAuth/Sources/Swift/SystemService/SecureTokenService.swift
+++ b/FirebaseAuth/Sources/Swift/SystemService/SecureTokenService.swift
@@ -125,7 +125,7 @@ final class SecureTokenService: NSObject, NSSecureCoding, Sendable {
     set { _requestConfiguration.withLock { $0 = newValue } }
   }
 
-  let _requestConfiguration: FIRAllocatedUnfairLock<AuthRequestConfiguration?>
+  let _requestConfiguration: UnfairLock<AuthRequestConfiguration?>
 
   /// The cached access token.
   ///
@@ -140,7 +140,7 @@ final class SecureTokenService: NSObject, NSSecureCoding, Sendable {
     set { _accessToken.withLock { $0 = newValue } }
   }
 
-  private let _accessToken: FIRAllocatedUnfairLock<String>
+  private let _accessToken: UnfairLock<String>
 
   /// The refresh token for the user, or `nil` if the user has yet completed sign-in flow.
   ///
@@ -150,7 +150,7 @@ final class SecureTokenService: NSObject, NSSecureCoding, Sendable {
     set { _refreshToken.withLock { $0 = newValue } }
   }
 
-  private let _refreshToken: FIRAllocatedUnfairLock<String?>
+  private let _refreshToken: UnfairLock<String?>
 
   /// The expiration date of the cached access token.
   var accessTokenExpirationDate: Date? {
@@ -158,7 +158,7 @@ final class SecureTokenService: NSObject, NSSecureCoding, Sendable {
     set { _accessTokenExpirationDate.withLock { $0 = newValue } }
   }
 
-  private let _accessTokenExpirationDate: FIRAllocatedUnfairLock<Date?>
+  private let _accessTokenExpirationDate: UnfairLock<Date?>
 
   /// Creates a `SecureTokenService` with access and refresh tokens.
   /// - Parameter requestConfiguration: The configuration for making requests to server.
@@ -170,10 +170,10 @@ final class SecureTokenService: NSObject, NSSecureCoding, Sendable {
        accessTokenExpirationDate: Date?,
        refreshToken: String) {
     internalService = SecureTokenServiceInternal()
-    _requestConfiguration = FIRAllocatedUnfairLock(initialState: requestConfiguration)
-    _accessToken = FIRAllocatedUnfairLock(initialState: accessToken)
-    _accessTokenExpirationDate = FIRAllocatedUnfairLock(initialState: accessTokenExpirationDate)
-    _refreshToken = FIRAllocatedUnfairLock(initialState: refreshToken)
+    _requestConfiguration = UnfairLock(requestConfiguration)
+    _accessToken = UnfairLock(accessToken)
+    _accessTokenExpirationDate = UnfairLock(accessTokenExpirationDate)
+    _refreshToken = UnfairLock(refreshToken)
   }
 
   /// Fetch a fresh ephemeral access token for the ID associated with this instance. The token
diff --git a/FirebaseAuth/Tests/Unit/AuthAPNSTokenManagerTests.swift b/FirebaseAuth/Tests/Unit/AuthAPNSTokenManagerTests.swift
index 0dec3c5e4ce..4cf6f8f29a9 100644
--- a/FirebaseAuth/Tests/Unit/AuthAPNSTokenManagerTests.swift
+++ b/FirebaseAuth/Tests/Unit/AuthAPNSTokenManagerTests.swift
@@ -62,7 +62,7 @@
     func testCallback() throws {
       let expectation = self.expectation(description: #function)
       XCTAssertFalse(fakeApplication!.registerCalled)
-      let firstCallbackCalled = FIRAllocatedUnfairLock(initialState: false)
+      let firstCallbackCalled = UnfairLock(false)
       let manager = try XCTUnwrap(manager)
       manager.getTokenInternal { result in
         firstCallbackCalled.withLock { $0 = true }
@@ -77,7 +77,7 @@
       XCTAssertFalse(firstCallbackCalled.value())
 
       // Add second callback, which is yet to be called either.
-      let secondCallbackCalled = FIRAllocatedUnfairLock(initialState: false)
+      let secondCallbackCalled = UnfairLock(false)
       manager.getTokenInternal { result in
         secondCallbackCalled.withLock { $0 = true }
         switch result {
@@ -104,7 +104,7 @@
       XCTAssertEqual(manager.token?.type, .sandbox)
 
       // Add third callback, which should be called back immediately.
-      let thirdCallbackCalled = FIRAllocatedUnfairLock(initialState: false)
+      let thirdCallbackCalled = UnfairLock(false)
       manager.getTokenInternal { result in
         thirdCallbackCalled.withLock { $0 = true }
         switch result {
@@ -178,7 +178,7 @@
       XCTAssertGreaterThan(try XCTUnwrap(manager.timeout), 0)
 
       // Add callback to cancel.
-      let callbackCalled = FIRAllocatedUnfairLock(initialState: false)
+      let callbackCalled = UnfairLock(false)
       manager.getTokenInternal { result in
         switch result {
         case let .success(token):
diff --git a/FirebaseAuth/Tests/Unit/Fakes/FakeAuthKeychainStorage.swift b/FirebaseAuth/Tests/Unit/Fakes/FakeAuthKeychainStorage.swift
index 251c1b719db..d40846b9882 100644
--- a/FirebaseAuth/Tests/Unit/Fakes/FakeAuthKeychainStorage.swift
+++ b/FirebaseAuth/Tests/Unit/Fakes/FakeAuthKeychainStorage.swift
@@ -21,9 +21,9 @@ import XCTest
 @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
 final class FakeAuthKeychainStorage: AuthKeychainStorage {
   // Fake Keychain. It's a dictionary, keyed by service name, for each key-value store dictionary
-  private let fakeKeychain = FIRAllocatedUnfairLock<[String: [String: Any]]>(initialState: [:])
+  private let fakeKeychain = UnfairLock<[String: [String: Any]]>([:])
 
-  private let fakeLegacyKeychain = FIRAllocatedUnfairLock<[String: Any]>(initialState: [:])
+  private let fakeLegacyKeychain = UnfairLock<[String: Any]>([:])
 
   func get(query: [String: Any], result: inout AnyObject?) -> OSStatus {
     if let service = queryService(query) {
diff --git a/FirebaseCore/Internal/Sources/HeartbeatLogging/HeartbeatStorage.swift b/FirebaseCore/Internal/Sources/HeartbeatLogging/HeartbeatStorage.swift
index 224426e086a..c99c55b4e7e 100644
--- a/FirebaseCore/Internal/Sources/HeartbeatLogging/HeartbeatStorage.swift
+++ b/FirebaseCore/Internal/Sources/HeartbeatLogging/HeartbeatStorage.swift
@@ -52,9 +52,9 @@ final class HeartbeatStorage: Sendable, HeartbeatStorageProtocol {
   // MARK: - Instance Management
 
   /// Statically allocated cache of `HeartbeatStorage` instances keyed by string IDs.
-  private static let cachedInstances: FIRAllocatedUnfairLock<
+  private static let cachedInstances: UnfairLock<
     [String: WeakContainer<HeartbeatStorage>]
-  > = FIRAllocatedUnfairLock(initialState: [:])
+  > = UnfairLock([:])
 
   /// Gets an existing `HeartbeatStorage` instance with the given `id` if one exists. Otherwise,
   /// makes a new instance with the given `id`.
diff --git a/FirebaseCore/Internal/Sources/HeartbeatLogging/WeakContainer.swift b/FirebaseCore/Internal/Sources/HeartbeatLogging/WeakContainer.swift
index f1dd1777aea..d034fce3c8c 100644
--- a/FirebaseCore/Internal/Sources/HeartbeatLogging/WeakContainer.swift
+++ b/FirebaseCore/Internal/Sources/HeartbeatLogging/WeakContainer.swift
@@ -18,3 +18,5 @@ import Foundation
 struct WeakContainer<Object: AnyObject> {
   weak var object: Object?
 }
+
+extension WeakContainer: Sendable where Object: Sendable {}
diff --git a/FirebaseCore/Internal/Sources/Utilities/FIRAllocatedUnfairLock.swift b/FirebaseCore/Internal/Sources/Utilities/UnfairLock.swift
similarity index 68%
rename from FirebaseCore/Internal/Sources/Utilities/FIRAllocatedUnfairLock.swift
rename to FirebaseCore/Internal/Sources/Utilities/UnfairLock.swift
index c94f3153db9..9028029763c 100644
--- a/FirebaseCore/Internal/Sources/Utilities/FIRAllocatedUnfairLock.swift
+++ b/FirebaseCore/Internal/Sources/Utilities/UnfairLock.swift
@@ -13,60 +13,54 @@
 // limitations under the License.
 
 import Foundation
-import os.lock
+private import os.lock
 
 /// A reference wrapper around `os_unfair_lock`. Replace this class with
 /// `OSAllocatedUnfairLock` once we support only iOS 16+. For an explanation
 /// on why this is necessary, see the docs:
 /// https://developer.apple.com/documentation/os/osallocatedunfairlock
-public final class FIRAllocatedUnfairLock<State>: @unchecked Sendable {
+public final class UnfairLock<Value>: @unchecked Sendable {
   private var lockPointer: UnsafeMutablePointer<os_unfair_lock>
-  private var state: State
+  private var _value: Value
 
-  public init(initialState: sending State) {
+  public init(_ value: consuming sending Value) {
     lockPointer = UnsafeMutablePointer<os_unfair_lock>
       .allocate(capacity: 1)
     lockPointer.initialize(to: os_unfair_lock())
-    state = initialState
+    _value = value
   }
 
-  public convenience init() where State == Void {
-    self.init(initialState: ())
-  }
-
-  public func lock() {
-    os_unfair_lock_lock(lockPointer)
-  }
-
-  public func unlock() {
-    os_unfair_lock_unlock(lockPointer)
+  deinit {
+    lockPointer.deallocate()
   }
 
-  public func value() -> State {
+  public func value() -> Value {
     lock()
     defer { unlock() }
-    return state
+    return _value
   }
 
   @discardableResult
-  public func withLock<R>(_ body: (inout State) throws -> R) rethrows -> R {
-    let value: R
+  public borrowing func withLock<Result>(_ body: (inout sending Value) throws
+    -> sending Result) rethrows -> sending Result {
     lock()
     defer { unlock() }
-    value = try body(&state)
-    return value
+    return try body(&_value)
   }
 
   @discardableResult
-  public func withLock<R>(_ body: () throws -> R) rethrows -> R {
-    let value: R
+  public borrowing func withLock<Result>(_ body: (inout sending Value) -> sending Result)
+    -> sending Result {
     lock()
     defer { unlock() }
-    value = try body()
-    return value
+    return body(&_value)
   }
 
-  deinit {
-    lockPointer.deallocate()
+  private func lock() {
+    os_unfair_lock_lock(lockPointer)
+  }
+
+  private func unlock() {
+    os_unfair_lock_unlock(lockPointer)
   }
 }
diff --git a/FirebaseCore/Internal/Tests/Unit/HeartbeatStorageTests.swift b/FirebaseCore/Internal/Tests/Unit/HeartbeatStorageTests.swift
index c48cea653f7..d8cec20a203 100644
--- a/FirebaseCore/Internal/Tests/Unit/HeartbeatStorageTests.swift
+++ b/FirebaseCore/Internal/Tests/Unit/HeartbeatStorageTests.swift
@@ -407,7 +407,7 @@ class HeartbeatStorageTests: XCTestCase {
     final class WeakRefs: @unchecked Sendable {
       // Lock is used to synchronize `weakRefs` during concurrent access.
       private(set) var weakRefs =
-        FIRAllocatedUnfairLock<[WeakContainer<HeartbeatStorage>]>(initialState: [])
+        UnfairLock<[WeakContainer<HeartbeatStorage>]>([])
 
       func append(_ weakRef: WeakContainer<HeartbeatStorage>) {
         weakRefs.withLock {
diff --git a/FirebaseFunctions/Sources/Functions.swift b/FirebaseFunctions/Sources/Functions.swift
index 8ab6d63e780..42a59a3e106 100644
--- a/FirebaseFunctions/Sources/Functions.swift
+++ b/FirebaseFunctions/Sources/Functions.swift
@@ -53,7 +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 = FIRAllocatedUnfairLock<[String: [Functions]]>(initialState: [:])
+  private static let instances = UnfairLock<[String: [Functions]]>([:])
 
   /// The custom domain to use for all functions references (optional).
   let customDomain: String?
@@ -61,7 +61,7 @@ enum FunctionsConstants {
   /// The region to use for all function references.
   let region: String
 
-  private let _emulatorOrigin: FIRAllocatedUnfairLock<String?>
+  private let _emulatorOrigin: UnfairLock<String?>
 
   // MARK: - Public APIs
 
@@ -341,7 +341,7 @@ enum FunctionsConstants {
     self.projectID = projectID
     self.region = region
     self.customDomain = customDomain
-    _emulatorOrigin = FIRAllocatedUnfairLock(initialState: nil)
+    _emulatorOrigin = UnfairLock(nil)
     contextProvider = FunctionsContextProvider(auth: auth,
                                                messaging: messaging,
                                                appCheck: appCheck)
diff --git a/FirebaseFunctions/Sources/HTTPSCallable.swift b/FirebaseFunctions/Sources/HTTPSCallable.swift
index b03d5b8fccd..b74e5b93c4b 100644
--- a/FirebaseFunctions/Sources/HTTPSCallable.swift
+++ b/FirebaseFunctions/Sources/HTTPSCallable.swift
@@ -43,7 +43,7 @@ public final class HTTPSCallable: NSObject, Sendable {
 
   private let options: HTTPSCallableOptions?
 
-  private let _timeoutInterval: AtomicBox<TimeInterval> = .init(70)
+  private let _timeoutInterval: UnfairLock<TimeInterval> = .init(70)
 
   // MARK: - Public Properties
 
diff --git a/FirebaseSessions/Sources/Installations+InstallationsProtocol.swift b/FirebaseSessions/Sources/Installations+InstallationsProtocol.swift
index 5a13dcfb838..158be0bee64 100644
--- a/FirebaseSessions/Sources/Installations+InstallationsProtocol.swift
+++ b/FirebaseSessions/Sources/Installations+InstallationsProtocol.swift
@@ -39,9 +39,9 @@ extension InstallationsProtocol {
   // TODO(ncooke3): Convert o async await ahead of Firebase 12.
 
   func installationID(completion: @escaping (Result<(String, String), Error>) -> Void) {
-    let authTokenComplete = FIRAllocatedUnfairLock<String>(initialState: "")
-    let installationComplete = FIRAllocatedUnfairLock<String?>(initialState: nil)
-    let errorComplete = FIRAllocatedUnfairLock<Error?>(initialState: nil)
+    let authTokenComplete = UnfairLock<String>("")
+    let installationComplete = UnfairLock<String?>(nil)
+    let errorComplete = UnfairLock<Error?>(nil)
 
     let workingGroup = DispatchGroup()
 
diff --git a/FirebaseSessions/Sources/Public/SessionsDependencies.swift b/FirebaseSessions/Sources/Public/SessionsDependencies.swift
index 9e0b3aafe6e..923bd1daea6 100644
--- a/FirebaseSessions/Sources/Public/SessionsDependencies.swift
+++ b/FirebaseSessions/Sources/Public/SessionsDependencies.swift
@@ -27,7 +27,7 @@ private import FirebaseCoreInternal
 @objc(FIRSessionsDependencies)
 public class SessionsDependencies: NSObject {
   private static let _dependencies =
-    FIRAllocatedUnfairLock<Set<SessionsSubscriberName>>(initialState: Set())
+    UnfairLock<Set<SessionsSubscriberName>>(Set())
 
   static var dependencies: Set<SessionsSubscriberName> {
     _dependencies.value()
diff --git a/FirebaseSessions/Sources/Public/SessionsSubscriber.swift b/FirebaseSessions/Sources/Public/SessionsSubscriber.swift
index bc15106e3c5..3f6225f81aa 100644
--- a/FirebaseSessions/Sources/Public/SessionsSubscriber.swift
+++ b/FirebaseSessions/Sources/Public/SessionsSubscriber.swift
@@ -27,8 +27,8 @@ public protocol SessionsSubscriber: Sendable {
 /// Session Payload is a container for Session Data passed to Subscribers
 /// whenever the Session changes
 @objc(FIRSessionDetails)
-public class SessionDetails: NSObject {
-  @objc public var sessionId: String?
+public final class SessionDetails: NSObject, Sendable {
+  @objc public let sessionId: String?
 
   public init(sessionId: String?) {
     self.sessionId = sessionId
diff --git a/FirebaseSessions/Sources/Settings/RemoteSettings.swift b/FirebaseSessions/Sources/Settings/RemoteSettings.swift
index 9f57b348b88..2e0e0080ab0 100644
--- a/FirebaseSessions/Sources/Settings/RemoteSettings.swift
+++ b/FirebaseSessions/Sources/Settings/RemoteSettings.swift
@@ -29,7 +29,7 @@ final class RemoteSettings: SettingsProvider, Sendable {
   private static let flagSessionsCache = "app_quality"
   private let appInfo: ApplicationInfoProtocol
   private let downloader: SettingsDownloadClient
-  private let cache: FIRAllocatedUnfairLock<SettingsCacheClient>
+  private let cache: UnfairLock<SettingsCacheClient>
 
   private var sessionsCache: [String: Any] {
     cache.withLock { cache in
@@ -41,7 +41,7 @@ final class RemoteSettings: SettingsProvider, Sendable {
        downloader: SettingsDownloadClient,
        cache: SettingsCacheClient = SettingsCache()) {
     self.appInfo = appInfo
-    self.cache = FIRAllocatedUnfairLock(initialState: cache)
+    self.cache = UnfairLock(cache)
     self.downloader = downloader
   }
 
diff --git a/FirebaseSessions/Tests/Unit/Mocks/MockSubscriber.swift b/FirebaseSessions/Tests/Unit/Mocks/MockSubscriber.swift
index 2f3845e70bc..6c4238312f8 100644
--- a/FirebaseSessions/Tests/Unit/Mocks/MockSubscriber.swift
+++ b/FirebaseSessions/Tests/Unit/Mocks/MockSubscriber.swift
@@ -30,10 +30,8 @@ final class MockSubscriber: SessionsSubscriber, Sendable {
     set { _isDataCollectionEnabled.withLock { $0 = newValue } }
   }
 
-  private let _sessionThatChanged = FIRAllocatedUnfairLock<FirebaseSessions.SessionDetails?>(
-    initialState: nil
-  )
-  private let _isDataCollectionEnabled = FIRAllocatedUnfairLock<Bool>(initialState: true)
+  private let _sessionThatChanged = UnfairLock<FirebaseSessions.SessionDetails?>(nil)
+  private let _isDataCollectionEnabled = UnfairLock<Bool>(true)
 
   init(name: SessionsSubscriberName) {
     sessionsSubscriberName = name