וַיֹּ֕אמֶר אַתָּ֥ה זֶ֖ה בְּנִ֣י עֵשָׂ֑ו וַיֹּ֖אמֶר אָֽנִי׃
Und er sprach: Du bist doch mein Sohn Esau? Und er antwortete: Ich bin es.
Rashi on Genesis
ויאמר אני AND HE SAID I AM — He did not say, “I am Esau”, but “It is I”.
Rashbam on Genesis
אתה זה בני עשו, it would appear that you are my son Esau.
Or HaChaim on Genesis
ויאמר אתה זה בני עשו He said: "you are indeed my son Esau" Isaac justified his bestowing the blessing. This verse is not a question. Jacob's reaction was a confirmation that Isaac was correct, of course.