Back when Twitter announced these changes, the company wrote only that the "stricter guidelines" in version 1.1 of the Twitter API would be released "in the coming weeks." And as of Wednesday, the new API has apparently arrived, though, again, not all of the API is yet available for viewing.
At the time, Twitter also told developers that they would have six months to migrate their apps from version 1.0 of the API to version 1.1. When that period expires, version 1.0 of the API will be deprecated, so apps that fail to update to use the new API will cease to work. It's not clear whether that six-month grace period started last month, when the new API was announced, or today.
As part of its new Developer Rules of the Road, Twitter explicitly states that it reserves the right to temporarily or permanently block access to its API form those developers it determines "have attempted to exceed or circumvent" its limitations, and says that it will "monitor [developers'] use of the Twitter API...to ensure your compliance with these Rules." The Rules also state that developers must use Twitter's own options as the defaults for common features such as photo uploading (via pic.twitter.com), suggested user lists, and trending topics. The rules further state that developers can "not attempt to interfere with, disrupt, filter, or disable any features of the Twitter API...including the content of embedded Tweets and embedded timelines." That seems to imply that showing content that Twitter embeds in tweets--iTunes Store previews, images, and the like--will no longer be optional for third-party clients.
And Twitter hints that ads may be coming to your timeline in third-party apps. The documentation states, "Twitter reserves the right to serve advertising via its APIs ("Twitter Ads"). If you decide to serve Twitter Ads once we start delivering them, we will share a portion of advertising revenue with you per our then-current terms and conditions." Though the company says it will allow developers to continue showing ads around tweets--in other words, elsewhere in an app or on a website--the only ads that can be displayed in the actual Twitter timeline are Twitter Ads.
None of the newly revealed API specifics are shocking, but they do make clear that Twitter is standing its ground, making life for third-party developers tougher and more restricted than ever before. Whether that will stifle innovation across third-party clients and apps remains to be seen.