Twitter has 105 million registered users, with 300,000 new users signing up every day, Stone said, opening Twitter's Chirp conference at the Palace of Fine Arts before an audience of just shy of 1,000 developers. That user figure is more than a recent estimate from comScore, which pegged Twitter's user base at 65 million.
The Twitter API (application programming interface) fields 3 billion requests per day, Williams said. "That's bigger than all but a couple of Web sites in the world," he said, claiming it makes Twitter "about the same size as Yahoo." He said the service has grown 1,500 percent each year on average since "Twitter Inc." was founded three years ago this month. The service is also fielding about 19 billion searches a month, Williams said, which compares to about 90 billion for Google.
But the growth has brought challenges. Twitter has struggled to keep up with the demands on its infrastructure, and Williams acknowledged the past two years have been a chaotic and not always pleasant time for the company.
His message for developers Wednesday was that Twitter is putting the difficult times behind it and can now offer a stable, reliable platform on which developers can build new applications.
"Even just in the past few months, Twitter is a qualitatively different company than it has been," Williams said. "We're out of the chaos to some degree, we're reacting better, we've built the infrastructure we need.
"What it means for you guys," he told developers, "is a more stable and organized platform for you to build on."
He addressed the fact that Twitter has started releasing some of its own applications, putting it in competition with its developer community. Referring to the BlackBerry and iPhone applications the company recently released, Williams said he knew it was a "controversial decision" but that it had to be done.
"When we did the research we found we were underserving users," he said. "We had to have a core experience on these platforms just like we have on the Web. We were failing the ecosystem because we were not getting as many people as we could engaged."
The company has seen 100,000 new users sign up through the BlackBerry app in just a few days, and 1.7 percent of all Twitter posts come through the BlackBerry application, he said.
Making Twitter easier to use remains a key objective. "Twitter is too hard to use. It's amazing it has grown as big as it is given how hard it is to use," Williams said..
To illustrate the point, he said if you type "I don't get" into the Google search bar, the second auto-complete suggestion is "I don't get Twitter." That example drew laughs, but Williams said it's a serious problem the company has to address if it wants to keep expanding.
Twitter has four main priorities going forward, he said: keep improving its infrastructure, make the service easier to use, improve the relevance of "tweets" for users and make revenue.
Ease-of-use efforts will be focused in large part on mobile devices, where Williams still sees Twitter's future. "Mobile is clearly where the majority of use will happen," he said.
Better relevance will allow users to find what they want from the 55 million Twitter posts that he said are being created every day. The company serves 600 million search queries a day, he said, mostly through the Twitter search API. Until now the results have been presented mostly in chronological fashion -- presenting the most recent rather than the most relevant results.
The company has been experimenting with "Top Tweets," which try to present more relevant results, and it will continue to hone its algorithm to make results relevant. It will also expand its location capabilities, which are a big part of relevance because they allow people to find posts from people close to them or in particular locations.
A few weeks ago it began to incorporate city and neighborhood information into results. On Wednesday, it announced that it will provide information about specific landmarks. "You'll be able to click on Palace of Fine Arts and see what all the people there are saying in a search view -- but even that will just be the beginning," he said.
The company will talk a lot more about new APIs and its plans for making money over the next two days. "The revenue plan will be organic to Twitter, it will be user-beneficial and it will be ecosystem-friendly," Williams said.
He urged developers to look to the future. There will be "hundreds of millions of users" and "thousands of ways to use Twitter that haven't even been imagined yet," he said.
"It will be incorporated into our daily lives. There will be new capabilities that haven't been created yet. That's the type of world we want you to pour your creative minds into."
The Chirp conference comes at an important time for Twitter, which has been adding users at a fast clip but until this week had not come up with a plan for making money. That changed Tuesday with the launch of Promoted Tweets, through which some users will start to see promotional messages from Best Buy, Red Bull, Starbucks and other advertising partners at the top of Twitter search results.
Forrester analyst Josh Bernoff said placing ads in search results is a good place for Twitter to start. "Of all the places Twitter could include ads, this is the least obtrusive and the most relevant," he wrote in a blog post this week. "People will not desert Twitter for this. It's inevitable -- technology services need revenue."
But the company may soon move beyond that. Twitter said it will spend some time figuring out how the ads resonate with advertisers and end-users. After that it may soon start sprinkling them between its users' message timelines.
The conference continues Wednesday and Thursday with presentations about upcoming APIs and more details about Twitter's business plan.
