According to the Pixel 2's technical specification site, the will not come with any headphones in the box. Instead, you will find a USB-C to 3.5mm headphone adapter now. Yes, that means Google also just as Apple did with the iPhone 7 last year.
Including an adapter will make it possible to use your current headphones, but ultimately what Google probably wants is for you to fork over $159 for its Pixel Buds. On the other hand, Google is selling USB-C headphones through its online store, but at nearly the same price as the completely wireless Pixel Buds, what's the point?