Relicensing and the Right to Fork

When a vendor relicenses a project, the first question a buyer asks is whether anything can be done about it. The answer rests on a property of open source that survives the change. Code released under an open license carries that license with it permanently. A later decision to publish new versions under different terms does not erase the license on what came before. This is the legal foundation of the right to fork, and it is why every major relicense of the current wave produced a community continuation rather than a dead end.

Why the pre change code stays open

A relicense applies going forward. The version of a project that was published under an open license such as the Mozilla Public License or Apache 2.0 remains available under those terms. A vendor cannot, as a general matter, retroactively revoke a license that recipients already hold. So at the moment of a relicense there are two versions of the project: the last release under the old open license, which anyone may take and build on, and the new releases under the changed terms. The community fork starts from that last open commit and carries the open license forward. The fork is therefore not a workaround or a loophole. It is the open license doing exactly what it was written to do.

This is also why the effective date of a relicense matters so much. Everything before it is open. Everything after it is under the new terms. The precise boundary, and what depends on it, is covered in notice and effective dates in a relicense.

The forks the current wave produced

The recent relicensing events each generated a fork. As of August 2023, HashiCorp moved Terraform, Vault, Consul, Nomad, and Packer to the Business Source License 1.1, and the community continuation of Terraform is OpenTofu, now under a neutral foundation. Redis moved to a dual model with the Server Side Public License as of March 2024, and the fork is Valkey, which continued the last open version of Redis under an open license. Elasticsearch and Kibana moved to the Server Side Public License and the Elastic License as of 2021, and the fork led by a major cloud provider is OpenSearch. Each of these started from the last open release and carries an open license, which is the right to fork in practice. The fuller history of two of them is covered in the OpenTofu and Valkey fork story.

What a fork solves and what it does not

A fork removes the license restriction. If your concern is the competitive use limits of the Business Source License or the service obligations of the Server Side Public License, moving to an open fork takes that concern off the table, because the fork carries an open license that the Open Source Initiative recognizes. That is a real and often decisive benefit. Source available is not open source, and a fork lets a buyer return to genuine open source terms.

What a fork does not remove is the work. Adopting a fork is a migration with its own engineering cost, testing burden, and operational risk. It also asks the buyer to bet on the fork's long term health: its governance, its pace of development, and whether the community sustains it. A young fork backed by a neutral foundation is a different proposition from one that depends on a single sponsor. None of this makes forking wrong. It makes forking a decision that should be weighed against the alternatives rather than assumed to be free.

Weighing the fork against the other paths

The right to fork is one option among several. The others are negotiating a commercial license with the vendor, moving to a different alternative entirely, or holding the relicensed version as a known and contained position. The correct choice depends on how widely the affected component sits in your estate and how much migration you can absorb. A component with a small blast radius may be cheapest to fork. One that is deeply wired into many products may be cheaper to license commercially while a longer migration is planned. The way these paths are compared on a common basis sits on the relicensing pillar, and the fork itself is often confused with the broader point that source available is not open source.

A relicensing exposure review sizes each path so the fork decision is made on evidence rather than instinct. We are independent and buyer side. We take no vendor fees and resell no software, so the recommendation reflects your exposure and nothing else. This is commercial and licensing risk advisory, not legal advice. For interpretation of your right to fork in a specific situation, engage your own counsel.