You can watch live here, from 2.30pm BST today (May 2nd 2017). Many have speculated on a successor to the popular Surface Pro 4 - plus a sniff of news of Microsoft's mobile plans, but I think we'll have to wait until the BUILD conference in a week's time for anything like that. Today's event is all about 'Windows 10 S' - I'm guessing the 'S' is for 'Store' (only).
This variant will only allow Store-approved applications (UWP apps and UWP-wrapped Win32 apps, i.e. via Project Centennial), which should set most peoples' minds at rest about inadvertent malware installation. Mind you, for an upgrade fee, users who find the new version restricting will be able to pay to upgrade this to the full, more open Windows 10 that we use today.
PS. Images of new Windows 10 hardware are leaking online as from a sieve. E.g. this tweet:
more images of Surface Laptop in Burgundy color :-) pic.twitter.com/FQToijmYwr— WalkingCat (@h0x0d) May 2, 2017