LaunchDarkly vs open source
"Open source" is doing a lot of work in this category. Four of the main LaunchDarkly alternatives publish their source, under four different licences, with four different sets of strings attached. One of them is AGPL-3.0, which a large share of enterprise legal policies ban outright for network services. Another is not open source at all in the OSI sense. This page sets out exactly what each one licenses, what stays closed, and what running the thing yourself actually costs once the licence is free.
Go open source if data residency, compliance or vendor-pricing risk are driving the decision, and check your policy against AGPL-3.0 before you settle on Unleash. Stay on hosted LaunchDarkly if the driver is only cost, because a highly available flag service plus its pager rota generally costs more in engineering time than the SaaS bill it replaces.
Side by side
What each licence actually permits
LaunchDarkly is included as the baseline: proprietary, hosted only, no self-hosted edition at any price. Licences below are as published in each project's own repository or docs, read August 2026.
| Project | Licence | What stays closed | Free to self-host | The catch |
|---|---|---|---|---|
| LaunchDarkly | Proprietary | Everything | ✗ no edition exists | Pricing model changes are not negotiable from your side |
| GrowthBook | MIT (most of repo) | Several directories under a commercial Enterprise licence | ✓ unlimited traffic, 1 project | Experimentation needs your own data warehouse |
| PostHog | MIT expat, except ee |
The ee directory; a posthog-foss build strips it |
✓ yes | You are self-hosting an analytics platform, not a flag server |
| Flagsmith | BSD-3-Clause (core) | Enterprise Edition: RBAC, SAML/SSO, some DB integrations | ✓ yes | Access control is the thing most self-hosters end up needing |
| Unleash | AGPL-3.0-or-later | Enterprise: extra environments, RBAC, advanced SSO | ✓ yes, licence permitting | Many corporate policies prohibit AGPL for network services |
| Flipt | Fair Core (v2); SDKs MIT | Pro features behind a licence key | ✓ yes, for internal use | Source-available, not OSI open source; converts to MIT after 2 years |
Sources: GrowthBook repo · PostHog repo · Flagsmith · Unleash repo · Flipt licensing docs. Compiled August 2026.
The AGPL question, since nobody else raises it
Unleash's open-source server is AGPL-3.0-or-later. A significant number of comparison articles published during 2026 still describe it as Apache-2.0, and that is simply wrong. The distinction is not academic. AGPL extends copyleft obligations to software made available over a network, which is the exact deployment shape of a feature flag server, and a large share of enterprise legal policies therefore ban AGPL dependencies outright. If you work somewhere with an approved-licence list, check Unleash against it before you spend a sprint on the deployment. The commercial tier at $75 per seat per month exists partly to solve this, but that means the "free open-source option" you were counting on may not be available to you at all.
Source-available is not open source
Flipt v2 is under the Fair Core License, which its own documentation describes as a mostly-permissive non-compete licence. You can run it commercially and modify it. You cannot build a competing cloud offering from it, provide it as a managed service to third parties, or bypass licence checks on commercial features. Each version becomes MIT two years after release, and the SDKs are MIT today. For a company that just wants flags in Git, this is close enough to open source that the distinction never comes up. For a company whose own product would host flags for customers, it is a hard boundary, and it is better to discover it now than during legal review.
What self-hosting really costs
The licence fee is zero and the service is not. A flag server is on the critical path of every request that reads a flag: when it is unavailable, SDKs fall back to default values, and your carefully staged rollout silently reverts to whatever the code says. That means redundancy, a database with backups you have actually tested, monitoring, an upgrade cadence for security patches, and a person who gets paged. Estimated honestly, that is a recurring slice of an engineer's month. At loaded cost it routinely exceeds the $110 to $500 a month that a hosted plan would have cost.
Which is not an argument against self-hosting; it is an argument against self-hosting for the wrong reason. The two reasons that hold up are data residency and compliance, where the control plane must sit inside your perimeter and no SaaS price makes that acceptable, and structural pricing risk, where owning an MIT or BSD-3 codebase means a future pricing change is an inconvenience rather than a migration. Teams that switch purely to save the subscription usually find the saving was notional.
A reasonable decision order
1. Check your licence policy first. If AGPL is banned, Unleash self-hosted is out before you evaluate anything technical.
2. Decide whether the control plane must be yours. If compliance says yes, the shortlist is Flagsmith, GrowthBook, PostHog and Flipt, and cost is a secondary question.
3. If it is purely cost, price the hosted tiers honestly. ConfigCat Pro at $110 a month or GrowthBook Cloud at $40 a seat are often cheaper than the operational time you would spend, and both leave the source-available exit open.
4. Whatever you pick, wrap the SDK. One internal interface in front of the vendor SDK turns the next migration into a one-file change per service. It is an afternoon of work and it is the single best insurance against this whole problem repeating.
Common questions
FAQ: open-source feature flags
Which open-source feature flag tool has the most permissive licence?
GrowthBook and PostHog, both MIT, with Flagsmith close behind at BSD-3-Clause. All three place some enterprise features outside the permissive licence: GrowthBook keeps several directories under a commercial Enterprise licence, PostHog carves out its ee directory and publishes a posthog-foss build with proprietary code stripped, and Flagsmith puts RBAC and SAML in a closed Enterprise Edition. Unleash is AGPL-3.0-or-later, which is open source but copyleft and frequently prohibited by corporate policy for network services. Flipt v2 is Fair Core, which is source-available rather than open source at all.
Is Flipt open source?
Flipt v2 is source-available rather than open source in the OSI sense. It uses the Fair Core License, described in its own documentation as a mostly-permissive non-compete licence. You can read, modify and run the code commercially, but you cannot build a competing cloud or managed service from it, offer Flipt as a service to third parties, or circumvent licence checks on commercial features. Each released version converts automatically to MIT two years after its release, and all SDKs and client libraries are MIT already. For most internal users this is functionally equivalent to open source; for anyone building a platform product on top of it, it is not.
Is self-hosting feature flags actually cheaper?
The licence is free; the service is not. A production flag service needs high availability, because when it goes down your SDKs fall back to default values and your rollout state effectively disappears. Budget for redundant instances, a database, monitoring, an upgrade cadence and someone who owns the pager. That is realistically a fraction of an engineer's time every month, which at loaded cost frequently exceeds a $110 to $500 monthly SaaS bill. Self-hosting wins decisively on two grounds that are not about money: data residency and compliance requirements, and removing the risk that a vendor changes its pricing model underneath you.