At FOSSY 2026, the Software Freedom Conservancy presented findings on an ongoing violation of the Affero General Public License version 3 (AGPLv3) by Bambu Lab, a Chinese 3D-printer manufacturer that has captured 38-48% of the $500-3000 hobbyist printer market by 2025.
The violation centers on Bambu Studio, a modified version of PrusaSlicer—a widely-used open-source “slicer” program that converts 3D models into instructions for 3D printers. According to Bradley Kühn of the SFC, Bambu Lab initially distributed the modified PrusaSlicer without providing source code or an offer to provide it, contrary to AGPLv3 requirements. Community pressure forced a source release around 2022-2023, but the company employed what Kühn described as a sophisticated circumvention mechanism.
The strategy involves two dynamically loaded shared-library files (.so files) built from C++ source. These files call over the network to an application running on Bambu Lab’s servers, passing a User-Agent string as authentication to access extra functionality. Bambu Lab claims this User-Agent is a DMCA anti-circumvention mechanism, but according to Kühn, this arrangement violates the core principle of AGPLv3: preventing companies from running proprietary code on their servers while distributing GPL-licensed software to users.
“You can’t put part of your Affero-GPLed application on your web server and keep it proprietary,” Kühn stated, noting this is precisely what the AGPL was written to prevent.
The slicer software has a significant history in the 3D-printing community. Alessandro Ranellucci created the original open-source Slic3r and deliberately chose AGPLv3 to prevent exactly this scenario: “someone was going to do ‘Slic3r as a service’,” he said. Josef Prusa later forked it into PrusaSlicer, building a company around free software and open-source hardware.
The presentation was delivered by Kühn, Karen Sandler, and Denver Gingerich. The SFC indicated it has engaged the 3D-printing community on broader free-software and free-culture topics over the past six months, positioning the violation discovery as part of a larger activist opportunity.
Key facts
- Bambu Lab controls 38-48% of the $500-3000 hobbyist 3D-printer market as of 2025
- Bambu Studio uses dynamically loaded proprietary files that communicate with Bambu Lab’s servers to access extra functionality
- The violation involves passing a User-Agent string to authenticate access to server-side proprietary code
- AGPLv3 was specifically designed to prevent companies from keeping code proprietary when running it on servers
- The original open-source slicer creator chose AGPLv3 to prevent this exact business model