The Pushshift BETA API is up. Currently query terms are not supported in beta because the Elasticsearch cluster is still under development. However, you can request comments and submissions and filter by author, subreddit, link id, etc.
There are two sets of documentation...
Conversation
beta.pushshift.io/redoc
beta.pushshift.io/docs
Comments and submissions come in slightly out of order so if you want to make sure you get everything, you can sort and filter on the sid (the id Pushshift gives each object).
The BETA API is around 10-100x faster than production.
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I'll be adding more parameters and eventually will have the Elasticsearch cluster up for it.
You can also get a list of all seen subreddits from the API and filter subreddits by substrings in the subreddit name.