Google Pixel and Pixel XL are indeed IP53 certified for dust- and splash-resistance
According to Droid-life, Google confirmed that its two new smartphones are IP53 certified. As we previously explained, the 5 in this rating means the devices are dust-resistant (though not completely dust-proof), but the 3 doesn't really mean they're also water-resistant. A more appropriate term to use for IPx3 certified products is splash-resistant. The official description for devices that are IPx3-rated is: "water falling as a spray at any angle up to 60-degrees from the vertical shall have no harmful effect" on them. Thus, your Pixel will be able to take some splashes if you use it while it's raining, but dunking it in water is certainly not something that you should do.
When it comes to dust- and splash-resistance, the Google Pixel and Pixel XL are similar to the HTC 10, which is also IP53 certified.
Already available to pre-order in the US and several other markets, the Pixel and Pixel XL will be released on October 20. Are you planning to get any of them?