The 2.6.41 release of Redshift gained popularity for being one of the most "production-hardened" versions before the major shift toward the 3.0 core. For Windows users on Houdini, this version offered:

Once Houdini is launched, check the "Render" menu. If "Redshift" appears and the shelf tools load without errors, your plugin is verified and active. Key Features in the Houdini Integration

Redshift Renderer 2.6.41 Plugin for Houdini (Windows): A Verified Guide