Apple overlaps iOS versions from 7 to 28 days; the average is 13 days

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Want to downgrade your device to iOS 8.4.1? Yesterday you could, but today you can't.

This is because Apple keeps a tight leash on iOS updates. During the install process, the device (or iTunes, or Configurator, or GroundControl) must verify some information with Apple, specific to both the device and the iOS build. Apple's servers analyze the info, then send back a one-time key to permit the installation. So at any time, Apple can stop "signing" the iOS update, effectively stopping all installs.

(This process doesn't affect you if you are already running the OS, only if you are installing or re-installing it.

After a new release, Apple always shuts down the old release. But it doesn't shut it down immediately. It waits a week or two first. I don't know the exact reason for the "signing window" to stay open. Maybe it's to give extra time for companies in the middle of a large deployment to get organized. Maybe it's to allow individuals who accidentally upgraded too early to change their minds. But when Apple stops signing that old release, it effectively forces your hand, and any iOS install then MUST go to the latest version.

Unfortunately, Apple has never announced in advance when it will stop signing an older release. This makes planning, well, a challenge.

To help (a little), we've compiled a history of how long Apple's kept that window open, after an upgrade. Maybe history will be a guide.

iOS Version Days as latest version Days still signed after update
iOS 9.0.2 n/a n/a
iOS 9.0.1 7 days n/a
iOS 9 7 days 7 days
iOS 8.4.1 34 days 14 days
iOS 8.4 44 days 11 days
iOS 8.3 83 days 7 days
iOS 8.2 30 days 27 days
iOS 8.1.3 41 days 16 days
iOS 8.1.2 49 days 14 days
iOS 8.1.1 21 days 9 days
iOS 8.1 29 days 14 days
iOS 8.0.2 25 days 7 days
iOS 8.0.1 1 day 0 days
iOS 8 7 days 28 days
iOS 7.1.2 79 days 9 days

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dfeldman's picture

dfeldman

Joined: Oct 5, 2015

Does this impact devices that

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Does this impact devices that are still on 8.4.1 in any way. For example, if I'm using Configurator to manage devices that are currently on 8.4.1, will I lose any ability to do that?

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alexes's picture

alexes

Joined: Nov 4, 2013

You won't be able to install

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You won't be able to install 8.4.1 at this point, if say you have a device in recovery mode or needed to supervise a device, you'll need to put on an iOS version that Apple is signing, however operations on already supervised 8.4.1 devices should continue to work fine.

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dfeldman's picture

dfeldman

Joined: Oct 5, 2015

Thanks for the info!

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Thanks for the info!

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