Reading around looks like it was homegrown, headed up by two people from the New Republic.
From their about page:
"It's a new digital home for an old journalistic tradition. Think of it as a magazine that only runs cover stories—big, ambitious pieces intended to change the way you see the world or influence the course of policy. Investigations will take months, essays will be finely considered, the subjects we choose to write about will feel urgent and essential."
From their about page:
"It's a new digital home for an old journalistic tradition. Think of it as a magazine that only runs cover stories—big, ambitious pieces intended to change the way you see the world or influence the course of policy. Investigations will take months, essays will be finely considered, the subjects we choose to write about will feel urgent and essential."