Not open source. Any use is allowed except competing with the publisher. Two years after a version is released it is also under MIT.
On this page
What it does
The Functional Source License 1.1 lets you use, copy, change, build on and pass on the software for any purpose that is not a Competing Use. A Competing Use means making the software available to others in a commercial product or service that substitutes for the software, substitutes for another product the publisher already offers using the software, or offers the same or substantially similar functionality. The license names four purposes as permitted: your own internal use and access, non-commercial education, non-commercial research, and professional services you provide to someone who already holds the license. Sentry wrote the license and uses it.
Details
The license has two halves. The first is the restricted grant. The second is a separate, irrevocable grant of the MIT license that starts on the second anniversary of the day the publisher made that version available. In version 1.1 the second grant is added to the first one rather than replacing it, so from that date both are open to you. The date belongs to the version you installed and not to the project, so an old version can already be under MIT while the newest one is not.
What it allows and requires
Choose a category to see the full grant in one scannable list. Permissions show what the license allows, limits show what it withholds, and obligations show the conditions your release process must satisfy.
Permissions
Internal use
Using the software inside your own company, and access for your own people, is a permitted purpose.
Modify
You may change the software and build new works on it for any permitted purpose.
Distribute
You may pass copies on, as long as the use is not a competing one and the terms travel with the copy.
Patent use
The grant covers the publisher's patents, to the extent a permitted use would infringe them.
Limits
Competing use
You may not offer the software to others in a commercial product or service that substitutes for it, or for a product the publisher offers with it.
Use trademark
You may name the publisher as the origin of the software. The license grants no other right to its names or marks.
Patent claim
If you claim the software infringes a patent, your patent license under these terms ends immediately.
Hold liable
The authors disclaim warranty. Recipients cannot hold them liable for damages arising from the software, except where law forbids that disclaimer.
Obligations
Include license
Include a copy of these terms, or a link to them, with every copy, change or new work you pass on.
Include copyright
Leave every copyright notice that came with the software in place in anything you pass on.
Future license
Two years after a version was made available, that version is also available to you under MIT.
What FSL-1.1-MIT requires when you ship
FSL-1.1-MIT is readable source with use limits. The work is to match your use to the written grant, then keep the text on the record so procurement can read it. Do not treat a source-available identifier as OSI-style open source because the code is on GitHub.
You are not making the software available to others in a commercial product or service that substitutes for it or offers substantially the same functionality.
You use it for your own internal work, for non-commercial teaching or research, or in services you provide to someone who already holds this license.
You include a copy of the terms, or a link to them, and leave every copyright notice in place, in any copy or change you pass on.
You have written down the version you depend on and the date the publisher made it available, because that date is when the MIT grant starts.
You have made no patent claim about the software. A claim against anyone ends your patent license immediately.
The duties named in FSL-1.1-MIT
The written grant is the source of the limits. These rows are the usual conditions teams have to match against their actual use, then keep on the record.
Include license
Include a copy of these terms, or a link to them, with every copy, change or new work you pass on.
Include copyright
Leave every copyright notice that came with the software in place in anything you pass on.
Future license
Two years after a version was made available, that version is also available to you under MIT.
Things to be aware of
- Teams read the MIT in the name as the license they have. MIT is the future grant. The terms that apply today are the restricted ones.
- Teams expect internal use to be the hard case. It is the permitted one. The case to look at is a product or a service you sell to others.
- Teams pin an old version and stop thinking about it. Every upgrade brings a version with its own two-year wait before the MIT grant.
What the Functional Source License 1.1, MIT Future License does not do
Search results often flatten Functional Source License 1.1, MIT Future License into a slogan. These are the usual misreads. FSL-1.1-MIT is a grant with conditions, not a permission to skip the paperwork below.
How FSL-1.1-MIT differs from nearby licenses
These licenses are often confused with FSL-1.1-MIT, but their release duties differ. Each row summarizes what the license requires when you ship. Open the linked page for the full checklist.
- FSL-1.1-MIT
- Not open source. Any use is allowed except competing with the publisher. Two years after a version is released it is also under MIT.
- FSL-1.1-ALv2
- Not open source. Any use is allowed except competing with the publisher. Two years after a version is released it is also under Apache 2.0.
- FSL-1.0-MIT
- Not open source. Any use is allowed except competing with the publisher. Two years after release the version changes over to MIT.
- BUSL-1.1
- Source available, not open source. Each version converts to an open license on its own Change Date, usually four years after release.
Common questions about Functional Source License 1.1, MIT Future License
Answers to common questions about what Functional Source License 1.1, MIT Future License requires, when its duties apply, and what evidence belongs with a release.
What is the Functional Source License 1.1, MIT Future License?
The Functional Source License 1.1 lets you use, copy, change, build on and pass on the software for any purpose that is not a Competing Use. A Competing Use means making the software available to others in a commercial product or service that substitutes for the software, substitutes for another product the publisher already offers using the software, or offers the same or substantially similar functionality. The license names four purposes as permitted: your own internal use and access, non-commercial education, non-commercial research, and professional services you provide to someone who already holds the license. Sentry wrote the license and uses it.
What does FSL-1.1-MIT require when you ship a product?
You are not making the software available to others in a commercial product or service that substitutes for it or offers substantially the same functionality. You use it for your own internal work, for non-commercial teaching or research, or in services you provide to someone who already holds this license. You include a copy of the terms, or a link to them, and leave every copyright notice in place, in any copy or change you pass on. You have written down the version you depend on and the date the publisher made it available, because that date is when the MIT grant starts. You have made no patent claim about the software. A claim against anyone ends your patent license immediately.
Is FSL-1.1-MIT open source?
Not in the OSI sense. FSL-1.1-MIT is source-available: you can read the code, but the grant restricts how you may use it. Read the actual text.
How is FSL-1.1-MIT different from Functional Source License 1.1, Apache 2.0 Future License?
FSL-1.1-MIT asks this: Not open source. Any use is allowed except competing with the publisher. Two years after a version is released it is also under MIT. Functional Source License 1.1, Apache 2.0 Future License asks this: Not open source. Any use is allowed except competing with the publisher. Two years after a version is released it is also under Apache 2.0. Open the Functional Source License 1.1, Apache 2.0 Future License page for what that license requires when you ship. Do not treat the SPDX ids as interchangeable because the short names look similar.
Where do I record FSL-1.1-MIT for a buyer?
The catalog records FSL-1.1-MIT as source available, and as a license a network deployment does not clear. A network distribution review item therefore appears on the checklist for SaaS and mixed projects, and publishing stays blocked until a person confirms it. The identifier is a templated one, so the fetch never lands it on confirmed, even when the text matches the publisher's copy word for word. A filled-in copy is labelled as the license with package-specific parameters instead of modified, and the text found in the package is put in front of you.
Where do I record FSL-1.1-MIT for a buyer?
The catalog records FSL-1.1-MIT as source available, and as a license a network deployment does not clear. A network distribution review item therefore appears on the checklist for SaaS and mixed projects, and publishing stays blocked until a person confirms it.
The identifier is a templated one, so the fetch never lands it on confirmed, even when the text matches the publisher's copy word for word. A filled-in copy is labelled as the license with package-specific parameters instead of modified, and the text found in the package is put in front of you.
Related licenses
See also
The hub is the pillar for this cluster. Sibling licenses are the other spokes. Product FAQ links explain how SourceTrust records the duty, not the license text itself.
Practical guidance for procurement review, not legal advice. Confirm high-stakes use with counsel.