2007-10-01 : If one half of a split card has a converted mana cost of 3 or less and doesn’t have an {X} in its mana cost, Gaddock Teeg lets you cast that half.

2018-12-07 : A spell’s converted mana cost is determined only by its mana cost. Alternative costs (including casting a spell “without paying its mana cost”), additional costs, and cost reductions don’t affect a spell’s converted mana cost.