An Ongoing 3D-Printer AGPL Violation: What the Software Freedom Conservancy Told FOSSY

A license violation presented at FOSSY

At FOSSY 2026, three people from the Software Freedom Conservancy (SFC) presented an ongoing violation of the Affero General Public License version 3 (AGPLv3) involving 3D-printer software from Bambu Lab. Bradley Kuehn, Karen Sandler and Denver Gingerich described a case in which the circumvention the company uses is precisely what the AGPL was written to prevent.

From Slic3r to Bambu Studio

Alessandro Ranellucci created the slicer Slic3r and deliberately chose the AGPLv3: "I anticipated all this, because my biggest worry was that someone was going to do 'Slic3r as a service'," he told Kuehn. Around 18 active forks exist, the best known being PrusaSlicer, from Josef Prusa's company. Bambu Lab entered the market during the COVID hobby boom, and by 2025 it controlled 38 to 48 percent of the $500-3000 printer market, depending on the analyst report.

It shipped a modified PrusaSlicer as Bambu Studio under the AGPLv3 without source code or an offer to provide it, until pressure from the community forced a release around 2022 or 2023 that, as is usual for a first attempt, was not the actual corresponding source.

The dynamically loaded part

Bambu Studio asks users to download "a little more stuff", with the familiar choices of "Yes" or "Ask me later"; some functionality does not work until "Yes" is clicked. The extras are two shared libraries built from C++ source, loaded into the slicer through dlopen() calls that are visible in the released code. That thin layer calls over the network to an extensive 3D application on Bambu Lab's servers, passing a "key" that is simply a User-Agent string, identical for all clients. The company claims the string is a DMCA anti-circumvention mechanism.

For Kuehn, that is exactly what the AGPLv3 forbids: "You can't put part of your Affero-GPLed application on your web server and keep it proprietary." A user in Poland, Pawel Jarczak, reverse-engineered the User-Agent and the network code; Bambu Lab responded with a DMCA takedown notice, which GitHub honored. Jarczak still maintains the code in his slicer, OrcaSlicer, mirrored in an SFC repository as part of the baltobu project.

Firmware, funding and what users can do

Gingerich said Bambu Lab also violates the GPLv2 by not providing the source for a Buildroot-based Linux and other copyleft components used in the firmware of some printer models. The company, he argued, has taken the "then, sue us" approach and simply stopped responding.

SFC's fundraiser for this work far exceeded its $250,000 goal, letting the organisation hire a full-time litigation attorney. Sandler warned that a GPL license is not "magic pixie dust": "If nobody holds anybody's feet to the fire, if nobody says 'wait a minute, you're not actually doing this', no one ever will do it." She urged buyers to ask for the complete corresponding source code for the devices they purchase.