Probably the same as the Instagram API, with hash tag #share2steem (seems this tag is used by some on Steemit that don't know its story and that it is useless) -
it all came to a crashing halt sometime after July 2019 - my last successful post using this tag on Instagram was this: thermoplastic's instagram Feed : 2019/07/01 14:35:18
Checking the hash tag on Instagram shows the following summary of posts: #share2steem, the last one July 9th 2019.
On the bottom of my last successful post you find:
the later link goes to my dead account on "share2steem.io" and shows a connection error.
So all in all, I "enjoyed" that feed for about 2 months, my first post using that API was 2019/05/31
Never used share2steem, but it's a pity that this useful service is also dead.
For me, it was short-lived, just a little more than a month. I wasn't using Instagram all that much (since my phone sucks, and the hack to post from a PC stopped working). So back to the same old. Steemit is "almost" useful, but not quite - I explained in a post on Facebook that I find it regrettable that you cannot embed content into a Steemit post (example: a Facebook video), thus I need to use my Blogger more often now where 1) this is possible and 2) I run my own ads! Since Blogger belongs to Google, I usually get better search results also.