The most frequent place you will see steam_64_api.dll errors is in modding communities, specifically for The Binding of Isaac: Repentance.
In Isaac, mods like "External Item Descriptions" or "Good Trip" require a mod loader (like Modding of Isaac) to hook into the game. This mod loader uses a custom steam_64_api.dll to bypass the game's internal Lua limits.
If you are an Isaac modder:
If you suspect your antivirus is the culprit:
A common mistake is confusing steam_64_api.dll with steam_api.dll. steam 64 api.dll
If you drop a 32-bit DLL into a 64-bit game folder, the game will crash immediately. Always check which version your game requires. You can check your game's bitness by looking at the Task Manager while it runs; if it says "32-bit" next to the name, you need the non-64 DLL.
Many DLL download sites provide outdated or incorrect versions of the file (e.g., a 32-bit DLL named as a 64-bit one). Placing the wrong architecture DLL can lead to system instability, crashes, and even Blue Screen of Death (BSOD) errors. The most frequent place you will see steam_64_api
If you are playing a legitimate Steam game that somehow needs a standard steam_api64.dll (not the underscore version), you can repair it:
If the game is a standalone mod or a non-Steam game that relies on Steam features, you may need to manually replace the file. If you drop a 32-bit DLL into a