Köln announced the extension on Monday, with technical director Lukas Berg explaining the club's thinking: "We are very happy that our shared path with Krissi continues.
"He has really earned this over the years and showed what qualities he has, especially during his time with the under-19s. The impression he left during pre-season with the professionals was also very good.
"With this extension we have created a framework in which he can develop as well as possible over the coming years."
Irmiev has been with Cologne since joining from JSG Erft 01 at under-11 level in 2017, progressing through every youth team at the Geißbockheim. He won the German under-19 championship with Köln's youth side in 2025, and trained with René Wagner's first-team squad during pre-season this summer, taking part in Köln's opening friendlies.
He has yet to make his professional debut and currently plays for Köln's reserve side.
The 19-year-old midfielder, born in Bulgaria, said the club had become like a second home: "Köln means a great deal to me, because I have gained many important experiences here since the under-11s, and the club has become a part of home for me. I extended because I feel very comfortable here, want to keep developing, and can still achieve a lot together with the club."