The K40 is one of Keurig's flagship brewers and was introduced as an upgrade to the B40, though the two models have the exact same specs.
Currently discontinued, the K40 has been replaced by the K-Classic, which offers many of the same features:
The only differences between the K40 and K-Classic are the K-Classic's slightly expanded brew sizes (6, 8, and 10 oz) plus its upgraded brewing system that ensures you're brewing with Keurig's latest and greatest technology for hotter, stronger cups.
You may also see 4 model numbers that look identical: K40, K45, K50, and K55.
What's the difference?
The K40 and K45 were originally released as Keurig's K-Elite brewers. Both came with the K-Cup variety pack, but the K45 also came with the water filter starter kit.
In 2015, Keurig rebranded the K40 and K45 K-Elite brewers as the K50 and K55 K-Classic brewers.