Is the salience augmentation data free?


It contains themes (main concepts in a tweet) as well as sentiment and it seems quite useful. Is there any cost to receive that extra data?


Filtering by sentiment - salience.content.sentiment or salience.title.sentiment is currently free. 

You will see themes appear in the returned data for many interactions, but this is still being developed. When it is fully implemented in the New Year it will be a service that we need to charge for. Unfortunately I don't have a pricing estimate for this feature at this time.