The 2025 horror film "Good Boy" is currently in theaters starting October 3, 2025. It is not yet available for free streaming on platforms like Netflix. The film will be available for purchase or rental on Amazon Prime Video about a month after its theatrical release, but free streaming on Prime is not expected as it is a Shudder original. "Good Boy" is planned to stream exclusively on the Shudder platform, a horror-focused streaming service, likely around early January 2026, although the exact Shudder release date has not been officially announced yet.
In summary, to watch the movie "Good Boy" now, the best option is to see it in a theater. For home viewing, wait for its digital rental/purchase on Amazon Prime or its upcoming release on Shudder.