Today Samsung UK officially responded to requests for an official statement saying the following:
"As we are currently investigating the reported issues with Galaxy S3 4.3 Jelly Bean update, the upgrading service has been temporarily suspended. We are committed to providing customers with the best possible mobile experience, and will ensure to resume the upgrading service at the earliest possibility."
So, the Galaxy S III update has been pulled from Kies and the OTA service has been suspended. We hope Samsung resolves this issues quickly and resumes the update rollout shortly. The Galaxy S III skipped Android 4.2.2 and its owners are waiting a year to get a newer Android version since the official 4.1 Jelly Bean ROM was released in 2012.
Things don’t seem to be going too well for Samsung’s Android 4.3 updates for various devices. After the Android 4.3 update for the Galaxy S III was put on hold because of major issues, it looks like AT&T might have done the same for the 4.3 update for the Galaxy S4. According to Android Police, the update has been pulled and AT&T is currently investigating some unmentioned issues, and is looking with “potential improvements” with Samsung.
This update was supposed to include Galaxy Gear support, but it looks like the Note 3 will be the only device on AT&T with support for Samsung's smart watch for a bit longer. So if you haven't received the update yet, you probably won't be getting it for a while yet.