Copyleft (GPL / AGPL)
Also: gpl, agpl
A licence style that requires derivative works to be released under the same terms. It matters for local AI tools: an AGPL tool built into a product you distribute can oblige you to open your own source.
Most open-source licences in local AI are permissive (MIT, Apache 2.0): you can build on the software with few obligations. Copyleft licences, chiefly the GPL and AGPL, take the opposite stance: if you distribute a derivative work, you must release it under the same licence, source included.
This is usually fine for personal or internal use, but it matters if you embed a copyleft tool in a product you ship. The AGPL goes further than the GPL by treating running the software as a network service as distribution. Several local-AI tools, including KoboldCpp and the Stable Diffusion web UIs, are AGPL, so it is worth knowing the distinction before you build on one commercially. This is separate from a model’s open weights licence.