On September 23, 2016, Google announced on its Webmaster Central blog (now the Search Central blog) that "Penguin is now part of our core algorithm". With the change, Penguin's data is refreshed in real time, so ranking changes take effect much faster, typically shortly after Google recrawls and reindexes a page, instead of waiting for the next periodic Penguin refresh.
Penguin also became more granular: Google said it now "devalues spam by adjusting ranking based on spam signals" rather than affecting the ranking of the whole site. In practice, spammy links are discounted instead of dragging an entire domain down, a significant softening compared with earlier Penguin releases that demoted sites wholesale.
As Search Engine Land reported, Penguin 4.0 was the last confirmed Penguin update: with the filter running continuously inside the core algorithm, Google said it would no longer announce refreshes. The wait it ended was real; the previous release, Penguin 3.0, had launched on October 17, 2014, leaving affected sites nearly two years without a chance to recover.