FAS

Short answer

A compiled, single-file binary of an AutoLISP/Visual LISP routine. Faster to load and obscures the source code.

A .fas file is the compiled form of a single .lsp source file, produced by the Visual LISP compiler (vlisp-compile in 'st' mode). It loads faster than source LISP and hides the implementation from buyers, which is why most paid LISP routines on marketplaces ship as .fas. FAS is the per-file equivalent of VLX (which bundles multiple files plus resources into one). Load a .fas exactly like a .lsp — with APPLOAD or (load "…").

Related guides

How to Load a LISP Routine in AutoCAD

Three reliable ways to load .lsp, .fas, and .vlx files into AutoCAD, plus how to add them to the Startup Suite so you never reload again.

Related terms

VLX

A compiled Visual LISP application that bundles multiple .lsp/.fas files, DCL dialogs, and resources into one file.

AutoLISP

Autodesk's dialect of LISP, built into AutoCAD since 1986, used to write custom commands and automate drawings.

Visual LISP

An extended LISP environment in AutoCAD that adds an IDE, debugger, COM access, and the ability to compile to FAS or VLX.