Before downloading the steam_api.dll file, ensure that your Steam client is up-to-date and that you've verified the integrity of the game files. Here are the steps to follow:

If your antivirus (Windows Defender, Avast, etc.) flagged the file:

Please verify your game files via Steam before requesting support. If the issue persists, check your antivirus quarantine logs.

, it usually means your antivirus software has quarantined the file or the Steam client can't find it in the game's directory. Quick Troubleshooting Guide

Do not use third-party DLL sites. Use Steam’s built-in repair tool.