Can I add memory or hard drives to the new Apple iMacs?

I haven't bought an iMac in a decade but I'm thinking about the new ones. I typically by a desktop model with relatively small amounts of memory and storage, because a new computer will be fast and by the time it slows down a year or two later memory and storage will be considerably cheaper. The old iMacs were inaccessible in terms of upgrading memory or storage, at least for the casual user. So my question is will I be able to increase memory or storage a year from now without voiding the warranty of a new iMac?