NOTE: Point/dot releases (example 11.3.1) may or may not come with an associated BridgeOS update. A forced BridgeOS update will be triggered if macOS 11.4 or newer is installed. This table shows how BridgeOS version 18P4556 is compatible with macOS version 11.0.1 – 11.3.1. I built a table to help visualize the current situation. You will now be running 11.3 and the matching bridgeOS version 18P4556. The Mac would boot into “macOS Update Assistant” and would then download the latest compatible BridgeOS update and install it for you.Īfter downgrading BridgeOS you will need to reinstall/downgrade 11.3 over the top of 11.4 or erase and install 11.3 again. If you don’t downgrade macOS to a compatible version and attempted to boot your Mac, you would be immediately prompted to update BridgeOS. You now need to downgrade macOS to version 11.3 to support the previous version of BridgeOS. You will need to downgrade to the minimum version of macOS that is supported by the version of BridgeOS that you are trying to downgrade to. You can now downgrade! The only problem is, the 11.3 version of BridgeOS does NOT support newer versions of macOS. You want to downgrade to the 11.3 compatible version of BridgeOS to see if that fixes the issue. Let’s go over an example.Īfter updating to Big Sur version 11.4, you are now are having issues with your speakers (sound processed through T2 chip). The BridgeOS version also supports previous versions macOS. BridgeOS supports the macOS version that’s released alongside it. The first thing to know about BridgeOS is that it has macOS version requirements. Apple leaves ONE previous version signed (for 7 days) so you can now downgrade to that version! BridgeOS and macOS Version Caveats The signing process follows iOS and is canceled usually about one week after the release of a new update. The difference here is that Apple WILL stop signing for previous versions of BridgeOS. We can then use the BridgeOS IPSW File to restore/revive BridgeOS to your T2 Mac. We can now download full BridgeOS IPSW Files directly from Apple the same way we do now with Apple Silicon M1 Macs. I’ve also talked about downgrading BridgeOS before, but this was ONLY for beta versions of BridgeOS to get back to production/final versions.Īpple Configurator took care of all the work in both above examples, downloading the prod/final version of BridgeOS for your hardware. You could always upgrade BridgeOS via automatic download with Apple Configurator 2. Now you want to downgrade to a previous version of BridgeOS so you can single out an issue or test the full update process again. Set this Mac on the shelf because you will never be able to take it through a full update process again until 11.5. Even if you boot back to recovery and install 11.3, BridgeOS will remain the same updated version. Now that this T2 Mac is on the latest version of BridgeOS it normally can not be downgraded. An example of this is if you upgrade a T2 Mac from 11.3 to 11.4. Part of that macOS Update process is updating BridgeOS. If you are a system administrator in charge of updating a large fleet of Mac testing is very important. Now you thinking that the new version of bridgeOS might be causing problems on your T2 Mac. So in this example, maybe you are getting audio cracking noise (has happened in the past). The T2 chip handles many things including, fan speed, battery, power, charging & sound (speakers & microphone). After the update, you’ve found that something is not working right. You updated to macOS Big Sur 11.4 from 11.3. Let’s go over a quick example of why you might want to downgrade BridgeOS. Why would anyone want to downgrade BridgeOS? Downgrading BridgeOS for troubleshooting & macOS Update workflow testing. Updating BridgeOS on a T2 Mac was a one way street. You can now downgrade T2 BridgeOS with an IPSW file and Apple Configurator 2 (for up to one week after the release of a new macOS update) You can now downgrade BridgeOS on your T2 Intel Mac (2017-2020) to a previous version with Apple Configurator 2!Įver since Apple released the very first T2 equipped Mac, some users wished that they had a way to downgrade to the previous version of BridgeOS.
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