Google is always tweaking its websites, the search engine is no exception. Lately, there haven't been that many changes, the search results page has stayed the same for longer than usual. But that doesn't mean Google stopped experimenting.
of the page that some users are seeing has the search options and filters placed on top.
That's not entirely new, the tablet version of the site does the same and there have been other experiments like this in the past.
The various search engine options, i.e. Web, Images, Videos and so on are placed on top of the results, maybe a more intuitive placement. Most people are used to tab menus, new users in particular may spot the options easier this way.
The Search Tools, the filters that enable users to narrow down results to a specific time, filter for visited sites and so on, open up below the main option tabs.