Google AdSense has an ad unit known as a link units, which are simple text based links that are ads that drive you to a page of ads. Normally, on the vertical display you get a maximum of 3 link units but some publishers are saying they are seeing 4 or more.
Here is what Google shows as an example:
A WebmasterWorld thread has some AdSense publishers saying they saw more than just the 2 or 3 links in this vertical ad links unit.
Here are some comments from the thread:
A couple of times today I have started to see 4 ads in a vertical display where there was just 3 ads in the past.
Definitely, for the past couple of days I have been seeing as many as five, yes 5, even on mobile devices.
Have you seen more ads showing in your ad links units?
Forum discussion at WebmasterWorld.