ECMWF Newsletter No.149, Autumn 2016, contains an article "ECMWF releases software for observational data" in the News section announcing release of ODB API.
Electronic version of the Newsletter in PDF format is already available to its readers, the article is on the page 10:
http://www.ecmwf.int/sites/default/files/elibrary/2016/16759-newsletter-no149-autumn-2016.pdf