Stardew Valley will not launch: check 32-bit and older OS compatibility

If launch fails, check whether the OS is 32-bit. The developer says the default version no longer supports 32-bit systems and provides a Compatibility branch. This is an option when OS compatibility is the cause.

Choose the compatibility branch on Steam

1. Right-click Stardew Valley in your library.
2. Open Properties → Betas.
3. Choose compatibility from the branch list.
4. Wait for the changed files to download, then launch again.

Choose the compatibility branch on GOG

1. Right-click Stardew Valley in the games list.
2. Open Manage Installation → Configure.
3. Select the compatibility branch under Beta Channels. The developer's article spells it Compatability.
4. Wait for the update and test the game.

What changes, and what stays the same?

The developer says both versions have the same game content and receive new content updates together. Multiplayer with standard-version players is supported. However, mods built for one version may not work in the other. After switching, testing the base game before enabling every mod helps distinguish causes.

The official article also lists Mac OS X 10.12 or earlier and Windows Vista or earlier as compatibility-version cases. Game-branch compatibility is separate from Steam/GOG's own OS support. This guide does not recommend using an old OS or downgrading.

If this branch still fails, provide your OS, storefront and mod use when contacting support.

Developer source: scope, Steam/GOG steps, content, multiplayer and mod exceptions: Stardew Valley developer — Compatibility guide