Windows 10 Mobile has yet to roll out for existing devices, but Microsoft has now offered a few more details.

Specifically, the company notes that a number of Windows Phone 8.1 devices will first have to receive firmware updates, and only after that will they be able to get the new Windows 10 Mobile update.

We're still not closer to getting a specific release date for Windows 10 Mobile, but at least now, the Microsoft representative offered a few more tidbits of information.

So far, nearly all Windows Phone updates gracing Lumia handsets came bundled with firmware updates. Windows Phone 8.1 came with Lumia Cyan and Windows Phone 8.1 Update 1 came with Lumia Denim, but Windows 10 Mobile will reportedly not come with any firmware update bundled.

This means that Windows Phone 8.1 devices will get firmware updates separately. These updates will arrive at the same time as Windows 10 Mobile for some devices, while for others, they will come before Windows 10 Mobile.

"For existing 8.1 devices, Win10 update is going to be only SW update, but in order to fix [a] few issue[s], there will be FW updates for some devices which are still based on 8.1 SW before they can receive [the] Win10 update," a Microsoft spokesperson tells Neowin.

"Right now we have not communicated what 8.1 devices will get updated and when but please have the latest SW on all your 8.1 [devices] in preparation of Win10."

The company has still not offered a specific release date for its new OS, but Windows Phone users are getting increasingly frustrated. Windows 10 Mobile was expected to roll out for existing Windows Phone devices back in December 2015 but faced delays.

It was then expected to arrive in January of this year, but subsequent reports revealed another delay, this time until February. More than halfway through February, Microsoft Mexico announced that Windows 10 Mobile would start rolling out on Feb. 29, only to later admit that its announcement was off.

It remains to be seen when Windows 10 Mobile will finally start reaching Windows Phone 8.1 devices, but Microsoft is staying mum on the matter. We'll keep you up to date as soon as more information becomes available, so stay tuned.