Description: I'm noticing that when using the completion handler variant of URLSession.dataTask(with:), the delegate method urlSession(_:dataTask:didReceive:) is not called—even though a delegate is set when creating the session. Here's a minimal reproducible example: ✅ Case where delegate method is called: class CustomSessionDelegate: NSObject, URLSessionDataDelegate { func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) { print("✅ Delegate method called: Data received") } } let delegate = CustomSessionDelegate() let session = URLSession(configuration: .default, delegate: delegate, delegateQueue: nil) let request = URLRequest(url: URL(string: "https://httpbin.org/get")!) let task = session.dataTask(with: request) // ✅ No completion handler task.resume() In this case, the delegate method didReceive is called as expected. ❌ Case where delegate method is NOT called: class CustomSessionDelegate: NSObject, URLSessionDataDelegate { func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) { print("❌ Delegate method NOT called") } } let delegate = CustomSessionDelegate() let session = URLSession(configuration: .default, delegate: delegate, delegateQueue: nil) let request = URLRequest(url: URL(string: "https://httpbin.org/get")!) let task = session.dataTask(with: request) { data, response, error in print("Completion handler called") } task.resume() Here, the completion handler is executed, but the delegate method didReceive is never called. Notes: I’ve verified this behavior on iOS 16, 17, and 18. Other delegate methods such as urlSession(_:task:didFinishCollecting:) do get called with the completion handler API. This happens regardless of whether swizzling or instrumentation is involved — the issue is reproducible even with direct method implementations. Questions: Is this the expected behavior (i.e., delegate methods like didReceive are skipped when a completion handler is used)? If yes, is there any official documentation that explains this? Is there a recommended way to ensure delegate methods are invoked, even when using completion handler APIs? Thanks in advance!