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The 600 series is actually a relatively mature product line; there are only two models in this series currently, but there were many before them. The 900 series used to have the 980 and 985 in addition to the 960, but iRobot shifted its focus to the "e", "i", and "s" series. These are all brand new product lines, and I don't doubt that the e5, i7 and s9 won't be the last models in each one. Furthermore, I suspect the 600 and 900 series will be discontinued altogether in the next year or two. You just happened to be shopping for a Roomba while iRobot was changing their product naming scheme.