License Change Notice: MIT → Apache License 2.0

[cbuahin]

License Change Notice: MIT → Apache License 2.0

Effective: 08-12-2026 · Applies to: all commits and releases from this date forward
Project: openswmm.engine (and associated components)
Status: Project is currently in alpha; this change is made intentionally at this early stage.

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What's changing

Starting with v6.0.0-alpha.4, openswmm.engine is licensed under the Apache License, Version 2.0 instead of the MIT License.

Releases and tagged versions published before this date remain available under their original MIT terms. This change only affects code going forward.

Why we're making this change now

We're doing this while the project is still in alpha, before a broad user base has built dependencies on the MIT terms specifically. Waiting until after wider adoption would make a change like this more disruptive — alpha is the right time.

The reasons for the switch:

1. Explicit patent protection. Apache 2.0 includes an explicit, irrevocable patent grant from every contributor, plus a patent retaliation clause. This protects everyone who uses this project — including commercial users — from patent claims related to contributed code. MIT has no equivalent language.
2. Attribution is easier to enforce. Apache 2.0 requires anyone who redistributes modified code to clearly state what they changed and to carry forward the project's NOTICE file. MIT only requires preserving the copyright notice. This gives contributors and the project stronger, clearer recognition when the code is reused or forked downstream.
3. Alignment with industry norms. Apache 2.0 is the standard license for large, widely adopted open-source infrastructure projects (Apache Foundation projects, most major cloud and data tooling, and much of the enterprise open-source ecosystem). Using it lowers legal review friction for organizations evaluating this project as a dependency.
4. No effect on our existing commitments. All prior and current contributors have signed the project's Contributor License Agreement, which already grants the project the right to relicense contributions. This change uses that existing right — it does not require, and has not required, retroactively altering anyone's original contribution terms.

What this means for you

• Users of released MIT versions: no change. You may continue to use, modify, and distribute those versions under the MIT terms they were published under.
• Users of the project going forward: covered by Apache 2.0, including its explicit patent grant.
• Contributors: no new action required. The existing signed CLA already covers this relicensing. See CLA.md for details.
• The core engine remains fully open for commercial use. Apache 2.0 is a permissive license — it does not restrict commercial use, does not require you to open-source your own downstream code, and does not impose copyleft obligations.

Questions

Open a discussion in the project's GitHub Discussions tab, or contact the Technical Manager (@cbuahin).

[cbuahin]

@wiesnerfriedman @ddspot @dickinsonre