Twitter makes its API free for public announcement accounts

Twitter announced Tuesday that it is making its API free to use for accounts posting public announcements such as weather alerts, transportation information, and emergency warnings.
The company said that verified government or public-owned services posting about public utility alerts will be eligible for free API usage.

One of the most important use cases for the Twitter API has always been public utility. Verified gov or publicly owned services who tweet weather alerts, transport updates and emergency notifications may use the API, for these critical purposes, for free.
— Twitter Dev

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