There have been rumours of discontent between the title-winning driver and title-winning team, led by CEO Barry Ryan, since late last year.
Those rumours suggested a shock split was on the table with Kostecki considering not seeing out the final year of his contract.
Speedcafe can now reveal that Kostecki has indeed decided to leave the team and is likely to be on the sidelines for at least the start of the 2024 Supercars season – if not the entire season.
It’s thought that a replacement has been lined up with Todd Hazelwood the favourite to take over the #99 Camaro.
Hazelwood has long been expected to be named as an Erebus co-driver for this year, the fact the deal hasn’t been announced a clue that he could be promoted to a full-time seat.
Kostecki and his management were unavailable for comment.
More to follow.