At which London theatre did Stranger Things: The First Shadow officially open?

Stranger Things: The First Shadow officially opened at London's Phoenix Theatre.

The stage play began previews at the Phoenix Theatre on November 17, 2023, before its official opening on December 14, 2023. The venue is a West End theatre in central London and served as the production's original home.

Written by Kate Trefry from a story by the Duffer Brothers, Jack Thorne, and Trefry, the play functions as a prequel to the television series. It explores Henry Creel's earlier life in Hawkins and adds background to the mythology that later surrounds Vecna.

The main source of confusion is that the production later transferred to Broadway. Its Broadway engagement opened at New York City's Marquis Theatre in April 2025, but that is not the London venue named in the question. Phoenix Theatre is therefore the specific canonical answer for the West End opening.