At five years old it's going to have IS. But check first. Just remember that until just a few months ago when the 400 f/2.8 II shipped, the 400 f/2.8 MkI was the holy grail of 400mm glass in the Canon Universe. It's a truly fabulous lens. The major benefit of the MkII is a radical weight loss. The MkI is a substantial 11.83lb / 5,370g vs the MkII at a svelte 8.48lb / 3,850g is a whole lot more manageable. But for the price I'd be jumping on it, subject to being in reasonable condition. If the lens does not work for you, you won't lose a penny re-selling it.