Twitter has added support for full-archive search to their API, allowing – in theory – third-party clients to retrieve every tweet ever posted on the service. From their blog:

The Full-Archive Search API combines the best aspects of two of Gnip’s most popular offerings to solve enterprise business needs with user experiences not previously possible. By pairing instant accessibility with the full archive of historical Tweets, we’ve created a new premium solution for our ecosystem of partners to deliver historical social data to their own clients.

Since Twitter added full-archive search to their app last year, I’ve been using the feature every day to find old stuff I or others tweeted in the past. There’s no word on pricing for Gnip customers, but hopefully apps like Tweetbot and Twitterrific will be able to take advantage of it. Developer documentation is available here.