Magento 2.1.1 not compatibile with PHP 7.1.0

Update - September 2017:

Magento 2.2 now officially supports PHP 7.1, so that's the Magento version you should aim for from now on if PHP 7.1 is something you want or need on your platform.

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Original - October 2016:

I am actually wondering if the DevDocs documentation is a mistake and maybe they meant PHP 7.0.10 instead of 7.1.0, that would make more sense to me.

That being said, I guess Magento 2.1.1 could be compatible with PHP 7.1, if you want to test it, just add this additional parameter to your composer commands to tell Composer to ignore the PHP version check for the time being:

composer install --ignore-platform-reqs

Update:

After raising an issue on Github, the requirements description now has been updated to reflect that PHP 7.1 is not supported at this point. The description was indeed a typo.

There are two possibilities:

1. The devdocs are wrong and PHP 7.1 is not supported
2. The requirement in composer.json is wrong.

Since Magento 2.1 was released before PHP 7.1, it is most likely option (2) and the requirement in composer.json has just not been updated yet.

But you can ignore it and install Magento anyways, if you add the --ignore-platform-reqs argument to your composer install command.

Update: As confirmed by https://github.com/magento/magento2/issues/7663, Magento 2.1 is not compatible with PHP 7.1

Update 2: There has been a merged PR for 7.1 compatibility that will be part of the magento-2.2 release. See https://github.com/magento/magento2/pull/8609#issuecomment-281743983

I didn't do composer install --ignore-platform-reqs just to make sure that I'm not running anything else on the server (or missing something) that's incompatible with M2.

In order to make it work I downgraded to PHP version 7.0.11 on my server and that did the trick so Magento 2.1.1 is compatible with PHP version 7.0.11 and not PHP 7.1.0