When the question was asked on Christian hermeneutics the response was both:
Please read what I wrote. Jer. 28:5 has יִרְמְיָה (Yirmeyah) and Jer. 7:1 has יִרְמְיָהוּ (Yirmeyahu). As for your former comment, yes, that should have been the case, but that's not what happened. That's why there is no transliteration of the Tetragrammaton in the Septuagint. Ever.
Is the best pronunciation of yhwh yahweh?
Does both endings refer to the same full name of YHWH. In some verses the prophet's name is written as Yirmeyah, but in some other verses it is written as Yirmeyahu.
Which one is right?
Did the prophet change his name?