Valve has announced that the supply of physical Steam Link hardware devices is sold out. Whether the company is working on a new iteration or if it will discontinue the product entirely is still unknown.
The Steam Link was released in November 2015 when Valve also introduced Steam Machine hardware. Over the years it has seen numerous flash sales, indicating that the company was sitting on a significant number of units.
A year before the release of Steam Link, Google's Chromecast streaming stick started becoming popular in households worldwide, but didn't officially support game streaming to TVs.