Twitter has been broadcasting for quite some time that it would be making changes to the API that developers use to access it for apps and today the company is finally beginning to detail what those changes are. First and foremost, developers who create apps that perform traditional 3rd party Twitter client functions (like Tweetbot) will be limited to 100,000 users total before the developer must get "permission" and/or "work with [Twitter] directly." Current apps will be able to continue to function as normal, however once their "user tokens" double whatever they are today, these new restrictions will apply. Essentially, once any 3rd party app hits its user limit, the developer will need to have a "come to Twitter" moment at which something will happen, and the most likely scenario is that the app simply won't be able to take on more users.
In case those numbers and what they mean aren't very clear, well, it's getting hard to argue that the confusion isn't by design. To clarify, Twitter presented a "quadrant" of types of apps and said it preferred that developers create analytics apps, Social CRM apps, and other types of essentially non-consumer-facing apps while avoiding traditional clients in the upper-righthand section of its chart. Again, Twitter said that developers "should not build client apps that mimic or reproduce the mainstream Twitter consumer client experience."
Twitter isn't saying exactly what will happen when those developers that have ignored Twitter's "guidance" run into their user caps beyond that it will require developers to work with the company and that it reserves the right to shut them down.
Beyond the above changes, Twitter is also limiting the number of API calls that can be made in an hour, which should act as a spam deterrent in some cases but in others will mean that anybody who wants to pull realtime analytics out of the Twitter firehose will need to work with the company more closely. Hardware manufacturers who ship pre-installed Twitter apps on devices will need to get those apps certified now, a move Twitter says is necessary since these pre-installed apps are so rarely updated.
Next: every app accessing Twitter's API must be authenticated. In other words, should any developer run afoul of the new rules and regulations Twitter had laid down here, the company will simply be able to revoke access, full stop.
One last change worth noting: going forward, Twitter will no longer issue "Display Guidelines," but instead give developers "Display Requirements." Right now, those requirements involve simple things like linking @usernames to Twitter profiles — but it's not difficult to imagine expanded requirements in the future. Those guidelines seem remarkably strict: for example they require that reply, retweet, and favorite "must always be visible" and that "No other social or 3rd party actions may be attached to a Tweet."
Developers will have six months to migrate over to the new API v1.1, at which point we'll have to see how Twitter decides to handle 3rd party clients that don't meet with its new requirements. However, the changes won't stop there, as Twitter is still planning on doing more with "Twitter Cards" that display more information within a specific Tweet.
Taken together, the new changes mean that any developer who creates an app must work with Twitter and as that app becomes more popular — especially if it's a "traditional" 3rd party client — Twitter's rules give the company more leverage over how that app will work. That could mean that we'll be seeing more and more partnerships between third party developers and Twitter (likely that involve displaying Twitter's ads and ensuring revenue flows in the right direction). What's much more likely is that we will see the most popular Twitter apps simply face a user cap. Whatever you believe Twitter's real intentions are with the limits, developers are about to run smack into Twitter's garden wall.