It's not required for arxiv authors to submit papers to journals. As far as I can tell "Language Models are Unsupervised Multitask Learners", (the GPT-2 paper) which has 9,786 citations, was never published in a journal.

The paper is going to be submitted to EMNLP next month. An early version is being released now to garner feedback and improve the paper before submission.

Sometimes that is included in the journal LaTeX template, but otherwise authors (in my field at least) typically won’t say where a paper is submitted before it’s accepted for publication there, or at the very least if it’s made it past the editorial rejection hurdle and been sent out for review

Probably your best bet for getting a feed heads up is to set a GScholar alert on the first author?

This is straight to ARXIV (its not even the final copy yet)

that's what arxiv used to be, but that's not what it is anymore