It is the old rendering path for Google Custom Search Engines:<p><a href="https:&#x2F;&#x2F;developers.google.com&#x2F;custom-search&#x2F;docs&#x2F;overview?hl=en" rel="nofollow">https:&#x2F;&#x2F;developers.google.com&#x2F;custom-search&#x2F;docs&#x2F;overview?hl...</a><p>Way back when Google first got VC, before they invented AdWords and got profitable, they explored a lot of custom business partner opportunities.  So there were a number of specialized Google search endpoints like &#x2F;linux, &#x2F;bsd, &#x2F;unclesam (search over Federal government websites).  These were maintained until about 2013 - they go through a different rendering path than the one that serves mainstream Google Search.  &#x2F;linux, &#x2F;bsd, &#x2F;unclesam, and a few others were decomissioned in 2013, soon before I left Google, but it looks like &#x2F;custom got a reprieve for whatever reason.  It&#x27;s actually been deprecated by the Custom Search Engine functionality linked above, but nobody&#x27;s gotten around to removing it.<p>Incidentally, you can also get a similar page (slightly different, its last update was around 2007 and it shows no ads) by setting your user agent to &quot;Mozilla 3.0&quot;.