Google I/O has historically always sold out in record fashion. Some years, it's sold out in under a minute. To combat this, and make it a bit more fair to those that aren't sitting at their desk refreshing the page over and over again, Google came up with the lottery. Essentially what happens here is you are given a few days to register your interest in attending Google I/O, which happens to take place May 18th through the 20th in Mountain View, CA instead of the usual San Francisco, CA. Once the site closes on March 10th, Google will then choose some lucky lottery winners to head to Google I/O in May. Tickets for the event are $900 per person, and academic attendees will pay $300. Space is limited, as always. Although it's likely to be not as limited this year seeing as they are doing Google I/O at the Shoreline Amphitheater in Mountain View.
As always, Google I/O is indeed a developers conference. We'll see the big keynote on May 18th, likely headlined by Google CEO, Sundar Pichai. The next two days are full of smaller sessions where developers can check out what Google is working on and how they can make their apps and games better than ever. Google, Apple and Microsoft all hold some pretty big developer conferences each year between May and July.
There's nothing confirmed for Google I/O just yet, however many are thinking we'll see something in regards to drones, self-driving cars and such. Seeing as this is at the Shoreline Amphitheater this year instead of Moscone Center, so there's no roof, making it easier to show off drones and self-driving cars. After all, Google has been working on self-driving cars for years and years now. With them bringing these cars to more and more cities, they've got to be close to mass manufacturing these cars. Especially with companies like Ford, GM and others working on their own self-driving cars. We'll definitely see Android N previewed at the keynote on May 18th, and a developer preview available later that day. Everything else is up in the air, as to whether we'll see at Google I/O this year.