"I am so happy."
Translation:Estoy tan feliz.
"Estoy tan contento." was accepted. I think that the use of the adverb "tan" indicates a temporary condition thus the "estoy" verb form is required. If we were describing a characteristically, happy person in English we would say they are a very happy person, not a so happy person. In this context, we would say "Soy muy contento (feliz)."