Today we're excited to announce the general availability of Account Activity API. Now developers can get started for free, upgrade to premium as they scale, and move to enterprise when they need even more subscriptions or enterprise functionality. https://t.co/AkMCDNOxbs — Twitter Dev (@TwitterDev) May 16, 2018

This API suits Twitters goal of feeding analytics and entertainment products, but it's a heavy blow to developers of third-part Twitter apps like Twitterrific and Tweetbot, and services like the already shutting down Favstar. Here's why:

There's no streaming connection capability as is used by only 1% of monthly active apps. Also there's no home timeline data. We have no plans to add that data to Account Activity API or create a new streaming service. However, home timeline data remains accessible via REST API. — Twitter Dev (@TwitterDev) May 16, 2018

So, to start with, third-party clients will have to discontinue features like live updates and activity information. Developers at The Iconfactory, which created the first-ever third-party Twitter Client, Twitterrific, have been sharing their reactions:

The public pricing that I'm seeing shows Twitter's Account Activity API pricing as $2,899/month to get activity updates… for 250 users.



Needless to say, we have more than 250 users.



It's possible an "enterprise" deal could be made, but it seems unlikely to be affordable. — Sean Heber (@BigZaphod) May 16, 2018

The math works out to about $10 per user a month to get push notifications. On a platform where people balk at spending 99¢… — Craig Hockenberry (@chockenberry) May 16, 2018

Make it $14 or more once associated costs are added and implemented, which would be untenable.

It's possible Twitter will work with developers to come up with affordable alternatives and even feature workarounds. There are no guarantees, though. And the bigger problem remains: Twitter, for years now, has through action and innaction been terrorizing the developers that helped make the service popular in the very early days of the service.

Favstar has already announced it's shutting down due to the uncertainty and constraints Twitter continues to introduce.

August 16, 2018 is the new end-of-life date for the old Streaming API. We'll have to wait and see how many third-party apps and services it takes along with it.