Based on whatever your search string is, the links move around, displaying what Google thinks would be the most useful for you. It's seemingly intelligent, but it's annoying me like hell considering the fact that my muscle memory hits the second link all the time for Google Images. Note above that the Google Images links are in different locations in the header. I can see why they're attempting to do this: they're making the second link the most "useful" or "relevant" - but it seems like their algorithm is off too. With the search string of "reddit" - the most "useful link" is Google Shopping. There's something definitely off here.
Isn't one of Nielsen's heuristics "Consistency and Standards?" Why do the locations of the elements in this header change so often? It's great to see Google experimenting; however, it's definitely introducing unpredictability and having a huge negative impact on the website's usability.