diff --git a/FirebaseAuth/CHANGELOG.md b/FirebaseAuth/CHANGELOG.md
index fd141940888..9a878b35ca7 100644
--- a/FirebaseAuth/CHANGELOG.md
+++ b/FirebaseAuth/CHANGELOG.md
@@ -1,3 +1,7 @@
+# Unreleased
+- [fixed] Updated most decoders to be consistent with Firebase 10's behavior
+  for decoding `nil` values. (#14212)
+
 # 11.6.0
 - [added] Added reCAPTCHA Enterprise support for app verification during phone
   authentication for Firebase Authentication (#14114)
diff --git a/FirebaseAuth/Sources/Swift/AuthProvider/FacebookAuthProvider.swift b/FirebaseAuth/Sources/Swift/AuthProvider/FacebookAuthProvider.swift
index 59cb2385425..b02ee16854d 100644
--- a/FirebaseAuth/Sources/Swift/AuthProvider/FacebookAuthProvider.swift
+++ b/FirebaseAuth/Sources/Swift/AuthProvider/FacebookAuthProvider.swift
@@ -36,7 +36,7 @@ import Foundation
 @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
 @objc(FIRFacebookAuthCredential) class FacebookAuthCredential: AuthCredential, NSSecureCoding,
   @unchecked Sendable {
-  let accessToken: String
+  let accessToken: String?
 
   init(withAccessToken accessToken: String) {
     self.accessToken = accessToken
@@ -56,11 +56,7 @@ import Foundation
   }
 
   required init?(coder: NSCoder) {
-    guard let accessToken = coder.decodeObject(of: NSString.self, forKey: "accessToken") as? String
-    else {
-      return nil
-    }
-    self.accessToken = accessToken
+    accessToken = coder.decodeObject(of: NSString.self, forKey: "accessToken") as String?
     super.init(provider: FacebookAuthProvider.id)
   }
 }
diff --git a/FirebaseAuth/Sources/Swift/AuthProvider/GameCenterAuthProvider.swift b/FirebaseAuth/Sources/Swift/AuthProvider/GameCenterAuthProvider.swift
index 82836ee81b0..935418f27d5 100644
--- a/FirebaseAuth/Sources/Swift/AuthProvider/GameCenterAuthProvider.swift
+++ b/FirebaseAuth/Sources/Swift/AuthProvider/GameCenterAuthProvider.swift
@@ -130,14 +130,14 @@
   @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
   @objc(FIRGameCenterAuthCredential)
   class GameCenterAuthCredential: AuthCredential, NSSecureCoding, @unchecked Sendable {
-    let playerID: String
+    let playerID: String?
     let teamPlayerID: String?
     let gamePlayerID: String?
     let publicKeyURL: URL?
     let signature: Data?
     let salt: Data?
-    let timestamp: UInt64
-    let displayName: String
+    let timestamp: UInt64?
+    let displayName: String?
 
     /// - Parameter playerID: The ID of the Game Center local player.
     /// - Parameter teamPlayerID: The teamPlayerID of the Game Center local player.
@@ -177,27 +177,20 @@
     }
 
     required init?(coder: NSCoder) {
-      guard let playerID = coder.decodeObject(of: NSString.self, forKey: "playerID") as? String,
-            let teamPlayerID = coder.decodeObject(
-              of: NSString.self,
-              forKey: "teamPlayerID"
-            ) as? String,
-            let gamePlayerID = coder.decodeObject(
-              of: NSString.self,
-              forKey: "gamePlayerID"
-            ) as? String,
-            let timestamp = coder.decodeObject(of: NSNumber.self, forKey: "timestamp") as? UInt64,
-            let displayName = coder.decodeObject(
-              of: NSString.self,
-              forKey: "displayName"
-            ) as? String else {
-        return nil
-      }
-      self.playerID = playerID
-      self.teamPlayerID = teamPlayerID
-      self.gamePlayerID = gamePlayerID
-      self.timestamp = timestamp
-      self.displayName = displayName
+      playerID = coder.decodeObject(of: NSString.self, forKey: "playerID") as String?
+      teamPlayerID = coder.decodeObject(
+        of: NSString.self,
+        forKey: "teamPlayerID"
+      ) as String?
+      gamePlayerID = coder.decodeObject(
+        of: NSString.self,
+        forKey: "gamePlayerID"
+      ) as String?
+      timestamp = coder.decodeObject(of: NSNumber.self, forKey: "timestamp") as? UInt64
+      displayName = coder.decodeObject(
+        of: NSString.self,
+        forKey: "displayName"
+      ) as String?
       publicKeyURL = coder.decodeObject(forKey: "publicKeyURL") as? URL
       signature = coder.decodeObject(of: NSData.self, forKey: "signature") as? Data
       salt = coder.decodeObject(of: NSData.self, forKey: "salt") as? Data
diff --git a/FirebaseAuth/Sources/Swift/AuthProvider/GitHubAuthProvider.swift b/FirebaseAuth/Sources/Swift/AuthProvider/GitHubAuthProvider.swift
index 75b914cbb7a..8765acaa7db 100644
--- a/FirebaseAuth/Sources/Swift/AuthProvider/GitHubAuthProvider.swift
+++ b/FirebaseAuth/Sources/Swift/AuthProvider/GitHubAuthProvider.swift
@@ -36,7 +36,7 @@ import Foundation
 @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
 @objc(FIRGitHubAuthCredential) class GitHubAuthCredential: AuthCredential, NSSecureCoding,
   @unchecked Sendable {
-  let token: String
+  let token: String?
 
   init(withToken token: String) {
     self.token = token
@@ -56,10 +56,7 @@ import Foundation
   }
 
   required init?(coder: NSCoder) {
-    guard let token = coder.decodeObject(of: NSString.self, forKey: "token") as? String else {
-      return nil
-    }
-    self.token = token
+    token = coder.decodeObject(of: NSString.self, forKey: "token") as String?
     super.init(provider: GitHubAuthProvider.id)
   }
 }
diff --git a/FirebaseAuth/Sources/Swift/AuthProvider/GoogleAuthProvider.swift b/FirebaseAuth/Sources/Swift/AuthProvider/GoogleAuthProvider.swift
index 0f41ac69ce3..38cfa40386e 100644
--- a/FirebaseAuth/Sources/Swift/AuthProvider/GoogleAuthProvider.swift
+++ b/FirebaseAuth/Sources/Swift/AuthProvider/GoogleAuthProvider.swift
@@ -38,8 +38,8 @@ import Foundation
 @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
 @objc(FIRGoogleAuthCredential) class GoogleAuthCredential: AuthCredential, NSSecureCoding,
   @unchecked Sendable {
-  let idToken: String
-  let accessToken: String
+  let idToken: String?
+  let accessToken: String?
 
   init(withIDToken idToken: String, accessToken: String) {
     self.idToken = idToken
@@ -62,13 +62,8 @@ import Foundation
   }
 
   required init?(coder: NSCoder) {
-    guard let idToken = coder.decodeObject(of: NSString.self, forKey: "idToken") as? String,
-          let accessToken = coder.decodeObject(of: NSString.self, forKey: "accessToken") as? String
-    else {
-      return nil
-    }
-    self.idToken = idToken
-    self.accessToken = accessToken
+    idToken = coder.decodeObject(of: NSString.self, forKey: "idToken") as String?
+    accessToken = coder.decodeObject(of: NSString.self, forKey: "accessToken") as String?
     super.init(provider: GoogleAuthProvider.id)
   }
 }
diff --git a/FirebaseAuth/Sources/Swift/AuthProvider/TwitterAuthProvider.swift b/FirebaseAuth/Sources/Swift/AuthProvider/TwitterAuthProvider.swift
index f9c32f9d5ad..d735ee0865b 100644
--- a/FirebaseAuth/Sources/Swift/AuthProvider/TwitterAuthProvider.swift
+++ b/FirebaseAuth/Sources/Swift/AuthProvider/TwitterAuthProvider.swift
@@ -37,8 +37,8 @@ import Foundation
 @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
 @objc(FIRTwitterAuthCredential) class TwitterAuthCredential: AuthCredential, NSSecureCoding,
   @unchecked Sendable {
-  let token: String
-  let secret: String
+  let token: String?
+  let secret: String?
 
   init(withToken token: String, secret: String) {
     self.token = token
@@ -61,12 +61,8 @@ import Foundation
   }
 
   required init?(coder: NSCoder) {
-    guard let token = coder.decodeObject(of: NSString.self, forKey: "token") as? String,
-          let secret = coder.decodeObject(of: NSString.self, forKey: "secret") as? String else {
-      return nil
-    }
-    self.token = token
-    self.secret = secret
+    token = coder.decodeObject(of: NSString.self, forKey: "token") as String?
+    secret = coder.decodeObject(of: NSString.self, forKey: "secret") as String?
     super.init(provider: TwitterAuthProvider.id)
   }
 }
diff --git a/FirebaseAuth/Sources/Swift/Backend/RPC/SignInWithGameCenterRequest.swift b/FirebaseAuth/Sources/Swift/Backend/RPC/SignInWithGameCenterRequest.swift
index 7d722326f71..34f94f87489 100644
--- a/FirebaseAuth/Sources/Swift/Backend/RPC/SignInWithGameCenterRequest.swift
+++ b/FirebaseAuth/Sources/Swift/Backend/RPC/SignInWithGameCenterRequest.swift
@@ -22,7 +22,7 @@ class SignInWithGameCenterRequest: IdentityToolkitRequest, AuthRPCRequest {
   typealias Response = SignInWithGameCenterResponse
 
   /// The playerID to verify.
-  var playerID: String
+  var playerID: String?
 
   /// The team player ID of the Game Center local player.
   var teamPlayerID: String?
@@ -40,7 +40,7 @@ class SignInWithGameCenterRequest: IdentityToolkitRequest, AuthRPCRequest {
   var salt: Data
 
   /// The date and time that the signature was created.
-  var timestamp: UInt64
+  var timestamp: UInt64?
 
   /// The STS Access Token for the authenticated user, only needed for linking the user.
   var accessToken: String?
@@ -57,10 +57,10 @@ class SignInWithGameCenterRequest: IdentityToolkitRequest, AuthRPCRequest {
   /// - Parameter salt: A random string used to compute the hash and keep it randomized.
   /// - Parameter timestamp: The date and time that the signature was created.
   /// - Parameter displayName: The display name of the Game Center player.
-  init(playerID: String, teamPlayerID: String?, gamePlayerID: String?,
+  init(playerID: String?, teamPlayerID: String?, gamePlayerID: String?,
        publicKeyURL: URL,
        signature: Data, salt: Data,
-       timestamp: UInt64, displayName: String?,
+       timestamp: UInt64?, displayName: String?,
        requestConfiguration: AuthRequestConfiguration) {
     self.playerID = playerID
     self.teamPlayerID = teamPlayerID
diff --git a/FirebaseAuth/Sources/Swift/MultiFactor/MultiFactorSession.swift b/FirebaseAuth/Sources/Swift/MultiFactor/MultiFactorSession.swift
index cc83e3f2f0d..42067fd30c3 100644
--- a/FirebaseAuth/Sources/Swift/MultiFactor/MultiFactorSession.swift
+++ b/FirebaseAuth/Sources/Swift/MultiFactor/MultiFactorSession.swift
@@ -46,7 +46,7 @@ import Foundation
       return .init(idToken: currentUser.tokenService.accessToken, currentUser: currentUser)
     }
 
-    init(idToken: String, currentUser: User) {
+    init(idToken: String?, currentUser: User) {
       self.idToken = idToken
       self.currentUser = currentUser
     }
diff --git a/FirebaseAuth/Sources/Swift/SystemService/SecureTokenService.swift b/FirebaseAuth/Sources/Swift/SystemService/SecureTokenService.swift
index 6bdee4c395a..a24ce10aabc 100644
--- a/FirebaseAuth/Sources/Swift/SystemService/SecureTokenService.swift
+++ b/FirebaseAuth/Sources/Swift/SystemService/SecureTokenService.swift
@@ -123,7 +123,7 @@ class SecureTokenService: NSObject, NSSecureCoding {
 
   /// The cached access token.
   ///
-  ///  This method is specifically for providing the access token to internal clients during
+  /// This method is specifically for providing the access token to internal clients during
   /// deserialization and sign-in events, and should not be used to retrieve the access token by
   ///     anyone else.
   var accessToken: String