Reading a model license: open weights are not all open

Open weights means a model's trained parameters are published for download, and the license attached to them sets the terms of use. That license can be an open-source software license such as Apache-2.0 or MIT, or a custom model license that adds conditions and often incorporates an acceptable use policy (AUP). In the custom licenses described below, the field-of-use limits are written in the incorporated policy. The Llama 4 Acceptable Use Policy lists prohibited uses, and one item names military, warfare, nuclear industries or applications, and espionage.

Software licenses applied to weights

In Section 2 of the Apache License, Version 2.0, dated January 2004, each contributor grants a perpetual, worldwide, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute the work. Section 3 adds a patent license that ends for a given work if the licensee files patent litigation alleging that the work infringes a patent. Section 4 sets redistribution conditions: give recipients a copy of the license, mark modified files, and keep the existing notices.

The grant lists actions. It lists no fields of use. Section 6 withholds trademark rights, which concerns names and marks, not purposes.

The MIT License, as posted by the Open Source Initiative (OSI), is shorter. It grants permission to deal in the software "without restriction," lists the rights included, and attaches one condition: the copyright and permission notice must appear in all copies or substantial portions of the software.

Neither text mentions model weights. The MIT text refers to software and its documentation files, and the Apache text refers to a work in source or object form. The Open Source AI Definition, version 1.0, addresses model parameters directly. It says they may be free by their nature or may need a license or other legal instrument, and it expects the question to become clearer as the legal system addresses it.

Custom model licenses

A custom model license is a text its publisher writes for its own models. The Llama 4 Community License Agreement, with a version effective date of April 5, 2025, is one example. The agreement's provisions include:

• Grant. A non-exclusive, worldwide, non-transferable, royalty-free limited license, where Apache's grant is perpetual and irrevocable.
• Redistribution. A copy of the agreement must accompany distribution, a "Built with Llama" notice must be displayed, a distributed model built from the materials must carry Llama at the start of its name, and an attribution notice must be kept.
• Scale threshold. If the products or services of the licensee or its affiliates had more than 700 million monthly active users in the month before the version release date, a license must be requested from Meta, which may grant it at its sole discretion.
• Termination. Meta may terminate for breach, and the licenses end if the licensee brings a claim against Meta or any other entity alleging that the materials or Llama 4 outputs infringe intellectual property rights.

The Gemma Terms of Use, last modified April 1, 2026, differ in detail. The page says its terms apply to the Gemma models listed in its appendix and sends readers to a separate license for Gemma 4. Two releases from one family therefore sit under different texts. The terms in Section 3.1 require the use restrictions to appear as an enforceable provision in any agreement governing downstream use or distribution. Section 3.2 adds that Google reserves the right to restrict usage remotely or otherwise when it reasonably believes the terms are violated.

What an acceptable use policy adds

Both custom licenses incorporate a separate policy by reference, so the policy is read together with the license. In the Llama 4 agreement, the policy is part of the redistribution conditions, which require use to comply with applicable laws and adhere to the policy. In the Gemma terms, Section 3.2 bars use for the restricted uses in the Gemma Prohibited Use Policy.

The Llama 4 policy lists prohibited uses under several headings, including violating the law or others' rights, activities that present a risk of death or bodily harm, deceiving others, and failing to disclose known dangers of an AI system. One item under the bodily-harm heading names military, warfare, nuclear industries or applications, and espionage, along with materials or activities subject to what the policy calls the International Traffic Arms Regulations (ITAR), maintained by the U.S. Department of State.

The policy page carries no date and says its most recent copy is kept at a web address, so a saved copy may differ from the current one.

What the Open Source AI Definition adds

The OSI definition sets a test that is independent of any single license. The four freedoms are to use the system for any purpose without asking permission, to study it, to modify it, and to share it. Access to the preferred form for making modifications is a precondition.

For a machine-learning system, that preferred form must include three elements: sufficiently detailed information about the training data, the complete source code used to train and run the system, and the parameters, each under OSI-approved terms.

Read against that text, a download of weights alone supplies one of the three elements. A license that carries a prohibited-use list contains terms of a different kind from the first freedom.

What to check

• Which text governs the weights: an open-source software license such as Apache-2.0 or MIT, or a custom model license?
• Does the license incorporate an acceptable use policy, and where is the current copy of that policy kept?
• Does any item in the policy's prohibited-use list name the field of use in question?
• Does the license require the use restrictions to appear in downstream agreements, or reserve a right to restrict usage remotely or otherwise?
• Which of the three elements in the Open Source AI Definition does the download supply?

The long read on model provenance goes further.

Sources

1. 1Apache License, Version 2.0 · Apache Software Foundation
2. 2The MIT License · Open Source Initiative
3. 3The Open Source AI Definition - 1.0 · Open Source Initiative
4. 4Llama 4 Community License Agreement · Meta Platforms (Llama 4 version effective April 5, 2025)
5. 5Llama 4 Acceptable Use Policy · Meta Platforms
6. 6Gemma Terms of Use · Google (last modified April 1, 2026)