Here are some more details surrounding this. The upgrade may not necessarily have a positive impact on the Greek stocks. Also, the original German article sourced from yesterday mentioned that it would be announced next Tuesday. Maybe this is a translation issue but saying yesterday "next Tuesday" is not referring to today but Tuesday of next week. At least that is my interpretation. Maybe someone can confirm this German comment from yesterday.
Monatelang liefen die Verhandlungen, in denen der Indexbetreiber MSCI mit institutionellen Anlegern diskutierte, ob Griechenland in die Klasse der entwickelten Märkte heraufgestuft wird. Am kommenden Dienstag folgt nun die Bekanntgabe der Entscheidung.
https://www.dw.com/el/πιθανή-αναβάθμιση-χα-ωφελημένοι-και-χαμένοι/a-76600145