C3 Brings Conversational Drafting to a Professional 2D CAD Program With 44 Years of History — and Lets Engineers Keep Their Drawings Entirely on Their Own Mac
Tetra720’s C3 Assistant describes-to-drafts across mechanical, architectural, electrical and scientific work by operating the CAD program’s own tools; runs with a private local model, no cloud required; one-time purchase, no subscription.
CHICAGO — October 7, 2026 — Tetra720 LLC today announced the general availability of C3 Assistant, a conversational drafting capability built into C3 (CADD300 Modern), its professional 2D CAD application for macOS. A user describes the drawing they need — in typed text or by dictation — and the Assistant produces it by operating more than 120 of C3’s own native drafting, dimensioning, annotation and editing tools. The result is not a picture and not a generated file: it is ordinary, fully editable CAD geometry in an open drawing, with associative dimensions, named layers, symbols and groups, and a single Undo step per request.
Unlike text-to-drawing services that assemble floor plans from a fixed set of templates, C3 Assistant drafts freely in whatever discipline the user works in. In testing, the same Assistant has produced dimensioned machine parts with GD&T feature control frames and hole tables, residential floor plans with walls, doors and windows, electrical schematics with netlists, optical and chemistry diagrams, structural details, pictorial and perspective views, and 3D wireframes — all using the same tools a drafter would use by hand, and all remaining editable afterwards with every tool in the program.
“Everything I’ve seen called ‘AI CAD’ makes a pretty picture, but it doesn’t build a real drawing out of real CAD primitives — lines, circles, arcs, text,” said John Christy, founder of Tetra720 and the author of C3 since its first version in 1982. “C3 Assistant does. It draws those primitives on real layers with real dimensions, and you edit the result with every tool in the program.”
Private by design
C3 Assistant works with the language-model provider the customer chooses, using the customer’s own account. It also runs with a fully private, locally hosted model, so that a firm’s drawings, prompts and project details never leave its own Mac — a configuration Tetra720 believes is unique among conversational CAD products. The Assistant is off by default and is enabled only after the user has read and accepted a plain-language consent statement.
A 44-year lineage
C3 descends directly from CADD/85, written by Christy in 1982 for the Hewlett-Packard HP-85 and listed in HP’s own software supplier catalog. Successive versions — CADD/87, CADD 200 and CADD 200/300 — ran on HP engineering workstations and were used at Hughes Aircraft Space & Communications Group. Drawings made with CADD/300 in the 1980s open in C3 today. The modern program is written in Swift, runs natively on Apple Silicon, and ships with a geometry test suite of more than 1,500 automated checks that runs on every change.
Beyond the Assistant, C3 is a complete professional 2D CAD system: eight dimension kinds with tolerances and named styles; a symbol library system with block attributes; hatching, tables with formulas, layers and paper-space layouts; DXF and DWG import and export verified against real public-works drawings; Gerber and Excellon export for printed-circuit-board fabrication; schematic capture with KiCad-compatible symbol and footprint libraries; PDF and image underlays with scale calibration; and a companion iPhone app that scans a room with LiDAR and delivers it into C3 as true, dimensioned wall geometry.
Pricing and availability
C3 is available now for macOS on Apple Silicon at tetra720.com as a one-time purchase of $1,995 per seat, with no subscription and no recurring fee. The C3 Pioneer Program, for credentialed professionals who want to test and shape the program, is also accepting applications at tetra720.com/beta.html.
About Tetra720
Tetra720 LLC, based in Chicago, is the successor to Tensegrity, Inc., which published the CADD/85 through CADD 200/300 line of CAD software for Hewlett-Packard computers beginning in 1982. Its product, C3 (CADD300 Modern), is a professional 2D CAD application for macOS. More information is at tetra720.com.
More at tetra720.com
Twenty-six drawings made by C3 Assistant, each with the prompt that produced it, are at tetra720.com/assistant.html. A full feature tour with screenshots of C3 at work is at tetra720.com/features.html, and the program’s history from CADD/85 to today — including the HP catalog listing and a 1986 CADD/300 drawing reopened in C3 — is at tetra720.com/story.html. The current release, downloadable logo, photos and full-resolution screenshots are at tetra720.com/press/. A demonstration, a drawing made to a writer’s own brief, and materials from the 1980s archive are available on request.
Media contact
John Christy, Founder, Tetra720 LLC — john@tetra720.com — tetra720.com
