How do I install IOS26 on my Iphone 8 plus?

You don’t. IOS 26 will not run on that device.

You don't!

That will never happen.

Even when it's out of beta, the iPhone 8 is not compatible with anything later than iOS 16.

You do not install iOS 26 on your iPhone 8 Plus – even after it becomes available this fall.

When the Phone 8 Plus first came out in September 2017 – more than seven and a half years ago – it ran iOS 11. It got five major updates. You can update it to the latest release of iOS 16 – but it will never receive iOS 17, 18, or 26. iOS 16 is the end of the line.

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FYI,, these are the iPhones that will be able to run iOS 26 when it comes out this fall. For the 11-series phones and the SE (2nd generation), iOS 26 will be their sixth major update. So although Apple has made no announcement, I would not count on the 11-series phones or the SE (2nd generation) being able to run iOS 27. Six major updates is already more than many other iPhones historically have gotten.

Note that only the 16-series phones, the 15 Pro, and the 15 Pro Max are compatible with Apple Intelligence. Other phones on this list can run iOS 18 now, and will be able to run iOS 26 when it comes out, but will not get the Apple Intelligence features.

An iPhone 8, iPhone 8 Plus, or iPhone X isn't capable of 17 or above; they require an A12 or better CPU. If it matters, 26 isn't yet publicly available.

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That's not possible, now or ever in the future when iOS 26 is officially released in the fall. iPhone 8 is forever frozen at iOS 16.7.11.

Your iPhone will never receive iOS 26. Your iPhone 8 Plus was discontinued on updates and didn’t receive iOS 17 or 18, so there’s no reason why it will receive the newest coming iOS 26.