How big are preprints? – Adam Day – Medium

"Current estimates put the total number of peer-reviewed research articles at around 100m. Growth is around 3.5–4m articles per annum and accelerating. ArXiv, the largest preprint server in the world, has published only 1.5m preprints and is currently putting out around 100k preprints per annum. ArXiv (and preprint servers generally) are accelerating too, but there’s still a lot of catching up to be done...."