Microsoft isn't just porting its Windows smartphone keyboard to iOS verbatim -- it's spicing things up in the process. Both Windows blogger Paul Thurrott and The Verge understand that iPhone users will get a fan-shaped one-handed keyboard. Based on the early peeks (including a few Verge pictures), the new mode resembles the touchscreen keyboard you got back in the Windows Vista days. Windows 10 Mobile already has a single-hand mode, but it only shunts the keys to one side -- this is designed more explicitly to fit your thumb.
Besides that, you're looking at a largely faithful rendition of the Windows keyboard, complete with Word Flow (swipe-to-type) and suggestions. The add-on still isn't publicly available -- you'll have to wait a few months for that. Look at this way, though: you'll at least know what you're likely to get when this new input method arrives.