why did halstead leave chicago med

Dr. Will Halstead left Chicago Med at the end of Season 8 after deliberately sabotaging an AI-assisted operating room system called OR 2.0 to expose its dangerous faults, which had already caused a patient's death. He accepted responsibility for the sabotage and resigned from his position at Gaffney Chicago Medical Center. After his resignation, the character moved to Seattle to reunite with his ex-fiancée Dr. Natalie Manning and her son, marking his final departure from the show at that time. Nick Gehlfuss, the actor who played Halstead, explained that he left the show because he felt he had taken the character as far as he could creatively after eight years. He wanted to explore new and different roles outside of Chicago Med. Gehlfuss has mentioned that leaving was a difficult but necessary decision for his career growth. Despite leaving, he left open the possibility of returning to the One Chicago universe if it made sense creatively, and he indeed returned in season 11.