diff --git a/AltServer/Anisette Data/RemoteAnisetteDataFetcher.swift b/AltServer/Anisette Data/RemoteAnisetteDataFetcher.swift
index 8f2706735b..2acb2968ba 100644
--- a/AltServer/Anisette Data/RemoteAnisetteDataFetcher.swift	
+++ b/AltServer/Anisette Data/RemoteAnisetteDataFetcher.swift	
@@ -87,6 +87,10 @@ actor RemoteAnisetteDataFetcher
     private static let timeout: TimeInterval = 90
     private static let placeholderSerialNumber = "C02LKHBBFD57"
 
+    // Apple rejects the client info anisette servers currently report with -23782 ("A Mac with macOS version 10.13 or later is required"),
+    // so identify as akd on macOS instead until servers report client info Apple accepts. Same override as iloader v2.4.1 (nab138/iloader@d319ce7).
+    private static let clientInfoOverride: (clientInfo: String, userAgent: String)? = ("<Mac15,7> <macOS;27.0;26A5378j> <com.apple.AuthKit/1 (com.apple.akd/1.0)>", "akd/1.0 CFNetwork/811.5.4")
+
     private let session: URLSession
     private let sessionDelegate = AnisetteSessionDelegate()
 
@@ -265,7 +269,7 @@ private extension RemoteAnisetteDataFetcher
             throw AnisetteError.remoteServerInvalidResponse(serverURL: serverURL)
         }
 
-        // 5. Assemble the result. deviceDescription and userAgent must be the server's, so they match the client that generated the anisette data.
+        // 5. Assemble the result. deviceDescription and userAgent must match the client info used for provisioning.
         let anisetteData = RemoteAnisetteData(machineID: machineID,
                                               oneTimePassword: oneTimePassword,
                                               localUserID: identity.localUserID,
@@ -279,6 +283,11 @@ private extension RemoteAnisetteDataFetcher
 
     func fetchClientInfo(from serverURL: URL) async throws -> (clientInfo: String, userAgent: String)
     {
+        if let clientInfoOverride = RemoteAnisetteDataFetcher.clientInfoOverride
+        {
+            return clientInfoOverride
+        }
+
         struct Response: Decodable
         {
             var clientInfo: String
diff --git a/AltStore/Operations/FetchAnisetteDataOperation.swift b/AltStore/Operations/FetchAnisetteDataOperation.swift
index 8d84fc1760..cbabc82c12 100644
--- a/AltStore/Operations/FetchAnisetteDataOperation.swift
+++ b/AltStore/Operations/FetchAnisetteDataOperation.swift
@@ -48,6 +48,10 @@ class FetchAnisetteDataOperation: ResultOperation<ALTAnisetteData>, @unchecked S
 {
     let context: OperationContext
 
+    // Apple rejects the client info anisette servers currently report with -23782 ("A Mac with macOS version 10.13 or later is required"),
+    // so identify as akd on macOS instead until servers report client info Apple accepts. Same override as AltServer and iloader v2.4.1 (nab138/iloader@d319ce7).
+    fileprivate static let clientInfoOverride: (clientInfo: String, userAgent: String)? = ("<Mac15,7> <macOS;27.0;26A5378j> <com.apple.AuthKit/1 (com.apple.akd/1.0)>", "akd/1.0 CFNetwork/811.5.4")
+
     // Set to Apple's X-Apple-I-MD-DATA to resynchronize the existing anisette data instead of fetching it normally.
     var resynchronizationData: String?
 
@@ -126,6 +130,12 @@ class FetchAnisetteDataOperation: ResultOperation<ALTAnisetteData>, @unchecked S
                     anisetteData.deviceDescription = sanitizedDescription
                 }
 
+                if let clientInfoOverride = FetchAnisetteDataOperation.clientInfoOverride
+                {
+                    // GrandSlam also rejects akd's client info unless it's sent with a matching user agent, including anisette data from AltServer.
+                    ALTAppleAPI.shared.authenticationUserAgent = clientInfoOverride.userAgent
+                }
+
                 self.finish(.success(anisetteData))
             }
             catch
@@ -245,7 +255,15 @@ private extension FetchAnisetteDataOperation
         let decoder = Foundation.JSONDecoder()
         decoder.keyDecodingStrategy = .convertFromSnakeCase
         
-        let response: Response = try await self.send(URLRequest(url: clientInfoURL), decoder: decoder, anisetteServerURL: serverURL)
+        let response: Response
+        if let clientInfoOverride = FetchAnisetteDataOperation.clientInfoOverride
+        {
+            response = Response(clientInfo: clientInfoOverride.clientInfo, userAgent: clientInfoOverride.userAgent)
+        }
+        else
+        {
+            response = try await self.send(URLRequest(url: clientInfoURL), decoder: decoder, anisetteServerURL: serverURL)
+        }
         
         // 2. Provision against this server unless we have a cached anisette identifier + adi.pb with the same client info.
         // A cached adi.pb from a different anisette implementation is no longer accepted, so discard it when the client info changes.