O365 SharePoint Online Compatibility Level

A colleague recently asked if its possible to create a Wave14 (SP2010) level site collection in a new Wave15 (SP2013) SharePoint Online tenant.
In testing, I've found that it depends.
If you are working in a Wave15 tenant that has been upgraded from Wave14, then the answer is yes. In the Wave15 SharePoint Online Admin Center under "Settings" there is the "Global Experience Version Setting in which you have the option to allow the creation of old version (SP2010) site collections.

 

 

 

 

Also, all pre-existing SP2010 sites will look the same after a tenant is upgraded from Wave14 to Wave15. Once the upgrade is done, site collection admins will need to upgrade each of their sites to take advantage of all the new features of SharePoint.
Its important to note this is a required step that should be completed within three months of the upgrade. If you don't get around to it, the MS Online Team will trigger the upgrade automatically at some point--They will contact you before they do so.

 

 But what about brand new Wave15 tenants (that are not upgrade from Wave14)?
What I've found through testing and PowerShell (the SPO Management Shell), is that new Wave15 tenants do not provide the ability to allow creation of old version (wave14) site collections.
First, from the SPO Admin Center, under Settings, the "Global Experience Version Settings" setting has "Prevent creation of old version site collections" selected, and the  Allow creation of old version site collections" is grayed out. You cannot modify this setting via the SPO Admin Center.

Using SPO Management Shell, even though attempting to change the minimum compatibility level by running Set-SPOTenant -minCompatibilityLevel 14 appears to succeed, as shown below, the setting will not take affect. Leaving the minCompatibilityLevel set to 15