In Greek, verbs are classified as "consonant-stem" or "vowel-stem". Vowel-stem verbs, aptly, have a vowel at the end of their stem. And in the Attic dialect, if this vowel is a short alpha, epsilon, or omicron, it contracts into the endings and makes a very distinctive conjugation pattern.
If the vowel is long, I would assume no contraction happens. But what about verbs ending in short iota or hypsilon? It seems likely that such stems exist, because Latin has quite a lot of i-stem verbs (the third conjugation -iō with short i, and the fourth conjugation with long ī).