Hi Paul!
The Lanczos filter in Flame is adjustable through the “Precision” numeric value when used through the Resize node for example. The “Precision” sets the Lanczos alpha which in turn determines the amount of lobes of the function. To have Lanczos4, you would set a “Precision” of 4. When importing/exporting a clip however, the Lanczos filter is locked at 5.25.