Microsoft today launched Windows 10 preview for phones. To get started, you’ll need to download the Windows Insider app from the Windows Phone Store.

Microsoft has already released multiple new Windows 10 preview builds, but those were limited to just PCs. Today’s preview is for smartphones, and it comes with a slew of new features.

More specifically, Microsoft is promising the following:

  • A browser rendering engine.
  • Full-size Background Image for Start: A new option to customize the start screen with a full-size background image.
  • More Quick Actions in Action Center: Windows Phone 8.1 is limited to four programmable quick actions, while Windows 10 gives you an expanded view with up to three rows.
  • Interactive Notifications: Notifications are now interactive, allowing you to take action directly, like dismissing an alarm or seeing images for maps. For example, for text messages, when the toast pops, you can quickly reply inline via text or voice.
  • Significantly enhanced speech-to-text capability: You can talk to virtually any data field you choose. Your words show up as you speak them — and punctuation appears automatically. This feature is smart enough to understand when to use “two” the number instead of “too” as in “also.”
  • More powerful Photos app: From your very first launch, Photos will show the aggregated set of all your local photos and all your OneDrive photos.

There is one major limitation worth emphasizing. In this build, Cortana is U.S.-only, English-only, and lacks some of the features already in Windows Phone 8.1. That said, Cortana will get better in future builds.

Until now, the Windows Insider app only worked for Microsoft employees. Today, Microsoft flipped the switch so that Windows Phone users who are part of the Insider program can install the first Windows 10 preview build, as long as they have one of the six compatible devices.

The Windows 10 preview works on the Lumia 630, Lumia 635, Lumia 636, Lumia 638, Lumia 730, and Lumia 830. “Expect the list to grow slowly at first but expand comprehensively over time,” Microsoft wrote. Your device will also need at least 8GB of storage and already have had Windows Phone 8.1 installed at the time of purchase (if you updated to Windows Phone 8.1, the preview won’t work).

New Windows 10 preview builds for phones will arrive as over-the-air (OTA) updates. They will be made available automatically after they are validated by engineers at Microsoft, who will first use them on their own phones.

Microsoft promises to continue pushing updates to testers’ phones “all the way up to the final build that goes out to all customers.” If you decide you no longer want to participate, Microsoft promises you can roll your phone back to the previous OS “any time you’d like.”

As for the limited list of supported devices, Microsoft is only supporting phones that have a recovery image available because it wants to be able to support restoring to older versions. This is why some “newer” devices aren’t supported yet:

We have a feature that will be coming soon called “partition stitching” which will allow us to adjust the OS partition dynamically to create room for the install process to be able to update the OS in-place. Until this comes in, we needed devices which were configured by mobile operators with sufficiently sized OS partitions to allow the in-place upgrade, and many of the bigger phones have very tight OS partitions.

Earlier this month, screenshots of Windows 10 for phones leaked out, showing a lot of what’s new. Yet those were old builds, and today’s release is the latest we’ve seen.

While this one is official, it still comes with a big warning label from Gabriel Aul, the leader of Microsoft’s Operating Systems Group’s Data and Fundamentals Team:

This is the earliest publicly available preview we’ve ever done for Windows on phones. This preview is still very much under development and you’re going to see some rough edges. We’re sharing it with you so you can be with us at every step, and provide your feedback to help make this the best release ever — because it’s the one made for you.

You will encounter bugs. You will see experiences that are clearly just not done yet, and UX that lacks polish at this point. DON’T WORRY! It will improve as we go and new features, stability and performance improvements, and more polished UX will come at each step.

You will likely feel like this first preview build for phones seems “less complete” or “earlier” than the PC. That’s true — it is. Although Windows 10 is built on shared code that runs on both PCs and phones, keep in mind that Windows 8.1 for PC was finished months earlier than Windows Phone 8.1, so the PC build has had more bake time.

Last but not least, Microsoft is also launching the phone version of Office for Windows 10 in the next few weeks. These free apps are supposed to ship for free with Windows 10 for phones, but they aren’t yet ready for preview.

In upcoming builds, Microsoft promises to include Word, Excel, PowerPoint, and the new Mail and Calendar apps from the Outlook team. IP-based messaging from Skype and others will also integrated directly into the Messaging experience.

In short, this Windows 10 preview already brings a lot to the table, but Microsoft has even more in the pipeline.