Check back here for live updates Wednesday from CNN's Heather Kelly, who'll be posting from the event hall in San Francisco.
First on stage is Terry Myerson, the executive vice president of Microsoft's operating systems group.
Joe Belifiore is up on stage now. He runs a group for PC, tablets and phones in the Operating System Groups. He's going to be talking about major Windows updates, starting with Windows phone 8.1 update.
He is showing off two new Windows Phones from new partners. There's one from Micromax another from Prestigio.
There's a new "action center" in Windows Phone 8.1. It's a notification and settings screen with battery percentage, notifications from social networks, and shortcuts for airplane mode and wireless connections. It can be brought up from any screen.
The lock screen is getting a makeover. Third parties can develop custom lock screens for the phone.
The start screen can be customized to pack in even more tiles and have a custom background image.
Windows Phone now has its own Siri, its name is Cortona.
Cortona? It's a town in Italy. That seems random. Then again, so did Siri.
Microsoft is calling it a "she" and the voice activated assistant has a slightly sexier voice than Siri. Why do we always want to anthropomorphize our digital assistants as women?
Cortona replaces search on the Windows Phone and can be accessed from the home screen. It does reminders, takes notes, sends messages, the usual.
There's a lot of Google Now influence on Cortana. The more you use it, the more it learns about your interests so that it can serve up customized information.
It determines who is in your inner circle based on your communications. If you want some down time, turn on quiet hours but allow a custom set of people to reach you. There are flight notifications, etc.
To get the necessary information about you, these personal assistant tools scan your calendars, email, and other personal accounts (with permission). Cortana also pulls information from Bing, Yelp and other databases of useful information.
Google Now is a powerful voice assistant that operates like Siri and Cortana, but it might suffer from a lack of personality. Should Google give in and give it a name?
There are a few glitches in the Cortana demonstration, but it's still in beta and seems to be working pretty well for a new hire.
To be clear -- that blue screen is my lame attempt at humor, not something that actually showed up at the keynote.
Cortana does something called "people reminders." You can set reminders for future phone calls to remind you to bring up specific topics when you call someone. The example is asking a sibling about their new puppy. Good for people who are really bad at casual chit chat?
Cortana takes app-specific requests such as putting something specific on your Hulu queue or seeing what a buddy is doing on Facebook.
They played a quick Jimmy Fallon sketch in which Siri hears about Cortana and says "Oh it's on, b*tch." Because they're both female voices, you see.
Windows Phone 8.1 supports S/MIME which allows users to send and receive signed and encrypted emails on their phone.
Windows phone has added a couple of other features for business users, including the encryption.
The store has been slightly redesigned with beefed up "partner engagement." Appealing to big app developers is key for Windows Phone if Microsoft wants to keep the platform competitive.
WiFi Sense knows who your Facebook friends and other contacts are. Turn it on and when a friend visits your house, they can hop on your WiFi network without you having to share your personal password.
New feature: shape writing! Drag a finger across the on-screen keyboard from letter to letter without lifting it up and it figures out what words you're trying to spell.
Very Swype, that feature. Good for those of us with clumsy thumbs.
Windows Phone 8.1 will be available to consumers with existing phones in the next few months.
New Windows Phones will start shipping with the new OS in late April and early May.
We're moving on from phones and looking at the Windows desktop updates.
A few older features that older Windows users missed are seeping back into Windows 8.1. Right click menus are back.
A new prompt shows you where new apps are installed. Apparently some users were having difficulty finding them after downloading them in the tile view.
The free Windows 8.1 update will be available starting next Tuesday, April 8.
David Treadwell is on stage. He has worked at Microsoft for almost 25 years.