Open Weights

The distinction matters more than the industry's vocabulary suggests. Open weights means the trained parameters are downloadable, so you can run the model on your own hardware. Open source, properly used, additionally means a license granting broad rights to use, modify and redistribute — typically with the training code and data pipeline available too.

Most models described in the press as "open source" are open-weight releases under custom licenses. Those licenses routinely carry restrictions a genuinely open license would not: revenue or user thresholds above which terms change, mandatory attribution, bans on training competing models, and in some cases geographic exclusions barring use in particular countries entirely.

A downloadable model, a public repository and a permissive-sounding announcement are all compatible with a license that forbids the thing you want to do.

Teams adopt open-weight models specifically to gain control — over cost, over data residency, over their own roadmap. A license restriction discovered after deployment defeats that entirely, and these terms are load-bearing for exactly the commercial use cases that motivate self-hosting in the first place.

That "open source" in a headline describes the license. It usually describes downloadability. The phrase has become standard press shorthand for any release you can download, and it gets applied to licenses that a software-licensing body would not recognize as open source at all. A public repository, downloadable weights and a permissive-sounding announcement are all compatible with terms that forbid the exact thing you want to do.

That the restrictions are theoretical. They bite precisely at the commercial uses that motivate self-hosting in the first place. Recent releases have carried revenue and monthly-active-user thresholds above which a separate written agreement is required; clauses barring use of the outputs to train a competing model; mandatory attribution; and — the one most likely to invalidate a deployment outright — geographic carve-outs excluding entire jurisdictions, in at least one case naming the United States and the EU. A team that read "open" as "ours to run" can discover after deployment that it never was.

That a license carries forward to the next generation. Terms are set per release. A lab that published permissively before can tighten when a model gets good enough to be worth protecting — which is exactly when you most want to use it. Never infer this generation's terms from the last one's.

Read the actual license file, not the announcement or the coverage. Four questions settle most cases: is commercial use permitted at all; are there revenue or user thresholds; is attribution or a no-compete clause mandatory; and is your country excluded? Note that restrictions often apply to the downloadable weights while the hosted API stays generally available, so say which path is actually open to you.