"steam_api64.dll" is a DLL file that is part of the Steam client application. Steam is a digital distribution platform developed by Valve Corporation that provides access to video games, game updates, and other related content. The "steam_api64.dll" file is specifically related to the 64-bit version of the Steam client and provides various functions and services related to the Steam API, including authentication, game updates, and cloud storage. The file is required by many video games that use the Steamworks API, which is a set of tools and services provided by Valve Corporation for game developers to integrate with the Steam platform. When a game is launched, it may use the "steam_api64.dll" file to access the Steam API and perform various tasks, such as verifying the user's ownership of the game, downloading updates, and accessing cloud storage.

If you encounter an error message related to "steam_api64.dll," it may indicate that the file is missing, corrupted, or not installed properly. In such cases, you may need to reinstall the Steam client application or the affected game to restore the missing file. It is worth noting that some antivirus software may flag the "steam_api64.dll" file as a potential threat, as it can be used to modify the behavior of video games. However, this file is an integral part of the Steam client and is not a virus or malware. If you encounter such warnings, you can usually ignore them or add the file to the list of exceptions in your antivirus software.