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Best Open Source Feature Flags of 2026

Updated · 4 picks · live pricing · affiliate disclosure

MIT-licensed warehouse-native flags; event data stays in your VPC; ~7K GitHub stars.

BEST OVERALL7.0/10

GrowthBook

MIT-licensed warehouse-native flags; event data stays in your VPC; ~7K GitHub stars.

Cloud Free 3 users plus OSS self-host free forever
Try GrowthBookSee full review

How it stacks up

  • OSS MIT free self-host

    vs Unleash Apache OSS

  • Cloud Free 3 users

    vs Flagsmith BSD-3 parity

  • Pro $40/seat upgrade

    vs PostHog MIT bundle

#2
Unleash6.0/10

From $75/mo

View
#3
Flagsmith5.4/10

From $45/mo

View

All picks at a glance

#PickBest forStartingScore
1GrowthBookBest OSS warehouse-native, MIT with event data in your VPC$40.00/mo7.0/10
2UnleashBest OSS original, Apache 2.0 since 2014 with environment isolation$75.00/mo6.0/10
3FlagsmithBest OSS BSD-3 self-hostable, Cloud-and-self-host feature parity$45.00/mo5.4/10
4PostHog Feature FlagsBest OSS bundled with analytics, MIT platform with replay and experiments$100.00/mo5.1/10

Quick pick by use case

If you only have thirty seconds, find your situation below and skip to that pick.

If I want Apache 2.0 OSS with the longest community lineage and granular environmentsUnleashUnleash OSS Apache 2.0 free forever; Cloud at $75/seat/mo upgrade. Around 12K GitHub stars since 2014.If I need event data to stay in my own data warehouse for HIPAA or GDPRGrowthBookGrowthBook OSS MIT free self-host; warehouse-native runs on Snowflake, BigQuery, Redshift, Postgres.If I want SaaS UI with the option to self-host at feature parityFlagsmithFlagsmith OSS BSD-3 free self-host; Start-Up at $45/mo upgrade with three seats. Cloud-and-self-host parity.If I want one MIT platform covering analytics, replay, experiments, and flagsPostHog Feature FlagsPostHog OSS MIT free self-host; Cloud Free 1M flag requests monthly bundled with full analytics platform.

Compare all 4 picks

Top spec
#1GrowthBook7.0/10$40.00/mo$480.00/yr—OSS MIT free self-host
#2Unleash6.0/10$75.00/mo$900.00/yr$420/yr moreOSS Apache 2.0 free
#3Flagsmith5.4/10$300.00/mo$3,000.00/yr$3,120/yr moreOSS BSD-3 free self-host
#4PostHog Feature Flags5.1/10$100.00/mo$1,200.00/yr$720/yr moreOSS MIT self-host free
#1

GrowthBook

7.0/10

Best OSS warehouse-native, MIT with event data in your VPC

Try GrowthBookSee GrowthBook alternatives

MIT-licensed warehouse-native flags; event data stays in your VPC; ~7K GitHub stars.

PlanMonthlyAnnualWhat you get
Cloud FreeFree—Free for up to 3 users with unlimited feature flags and unlimited experiments running directly against your warehouse
Pro$40.00/mo$480.00/yr$40 per seat a month with CUPED, sequential testing, multi-arm bandits, visual A/B editor, and premium support
Enterprise (cloud or self-host)CustomCustomCustom pricing with SSO/SAML, audit logs, approval flows, prerequisite flags, advanced metrics, and dedicated support
OSS (self-host)Free—MIT-licensed self-hosted free forever with unlimited users and unlimited traffic

GrowthBook is the MIT warehouse-native pick and the only catalog OSS option where event data never leaves the customer VPC on the SaaS UI. Founded 2020 in San Francisco by Graham McNicoll and Jeremy Dorn. MIT-licensed with around 7,000 GitHub stars by 2026. The wedge for OSS readers: experiments run directly against the customer's own Snowflake, BigQuery, Redshift, ClickHouse, or Postgres. The SaaS UI orchestrates queries and stores config only; event data never crosses the vendor boundary.

OSS self-host is MIT-licensed and free forever with unlimited users, flags, experiments, and traffic. Cloud Free covers up to three users with unlimited flags and unlimited experiments. Pro is the upgrade tier at forty dollars per seat monthly with up to fifty users plus CUPED, sequential testing, multi-arm bandits, and a visual A/B editor. Enterprise covers SAML SSO, audit logs, and approval flows at custom contract pricing.

The trade-off versus Unleash is OSS lineage; GrowthBook is newer than Unleash's 2014 origin. The trade-off versus PostHog is bundle scope; GrowthBook is flags-and-experiments-focused where PostHog bundles broader analytics. For OSS readers in HIPAA, FedRAMP, or EU GDPR territory, GrowthBook is the only fit.

Pros

  • MIT-licensed OSS self-host free forever with unlimited users, flags, and traffic
  • Only catalog OSS pick where event data never leaves the customer VPC
  • Cloud Pro at forty dollars per seat covers CUPED, sequential testing, multi-arm bandits
  • Around 7,000 GitHub stars by 2026; bootstrapped small-team since 2020
  • Cloud Free covers three users with unlimited flags and unlimited experiments

Cons

  • Smaller SDK ecosystem than LaunchDarkly or Unleash at this stage
  • Newer OSS lineage than Unleash (2020 vs 2014)
OSS MIT free self-hostCloud Free 3 usersPro $40/seat upgradeCloud Free 3 users plus OSS self-host free forever

Best for: OSS readers in HIPAA, FedRAMP, or EU GDPR territory who want a SaaS UI without sending event data to the vendor; modern data-warehouse teams.

Targeting
10
Rollout
8
DX
8
Value
9
Support
7
Try GrowthBook
#2

Unleash

6.0/10$420/yr more

Best OSS original, Apache 2.0 since 2014 with environment isolation

Try UnleashSee Unleash alternatives

Apache 2.0 open-source flags since 2014; ~12K GitHub stars; granular project plus environment isolation.

PlanMonthlyAnnualWhat you get
OSS (self-host)Free—Apache 2.0 licensed self-hosted free forever; the original open-source feature-flags project since 2014
Pay-as-you-go$75.00/mo$900.00/yr$75 per seat a month for hosted Unleash with 53 million API requests included monthly and 90-day flag metrics retention
EnterpriseCustomCustomCustom pricing with SAML SSO, RBAC, advanced governance, on-prem option, and 5-seat self-host minimum

Unleash is the Apache 2.0 OSS-original pick and the longest continuous open-source feature-flags lineage in the category. Founded 2014 in Oslo by Ivar Conradi Østhus, originally a side project at FINN.no, spun out as Bricks Software AS in 2017. Apache 2.0 licensed with around 12,000 GitHub stars by 2026. The wedge: granular project-and-environment isolation; each project can have unlimited environments and flag config is fully isolated across them.

OSS self-host is Apache 2.0 free forever with unlimited flags, environments, and self-host. Cloud Pay-As-You-Go is the upgrade tier at seventy-five dollars per seat monthly with fifty-three million API requests included monthly and 90-day flag metrics retention. Enterprise covers SAML SSO, RBAC, advanced governance at custom contract pricing with a 5-seat self-host minimum.

The trade-off versus GrowthBook is experimentation; Unleash ships basic A/B testing where GrowthBook ships full warehouse-native experiments with sequential testing and CUPED. The trade-off versus PostHog is bundle scope; Unleash is flags-focused where PostHog bundles analytics. For OSS-purist teams with strict dev-stage-prod separation, Unleash is the right call.

Pros

  • Apache 2.0 OSS original since 2014; the longest continuous OSS lineage in the category
  • OSS self-host free forever with unlimited flags and environments
  • Around 12,000 GitHub stars by 2026; the largest OSS feature-flags community
  • Granular project-and-environment isolation for strict dev-stage-prod separation
  • Cloud PAYG upgrade at seventy-five dollars per seat with 53M API requests

Cons

  • No native experimentation suite; pair with GrowthBook or Statsig for depth
  • Self-host enterprise tier requires a 5-seat minimum higher than smaller teams want
OSS Apache 2.0 freeCloud $75/seat upgrade~12K GitHub starsOSS Apache 2.0 free forever; cancel Cloud anytime

Best for: OSS-purist teams or orgs with strict dev-stage-prod environment separation who want the longest-running Apache 2.0 flags project.

Targeting
9
Rollout
8
DX
8
Value
10
Support
7
Try Unleash
#3

Flagsmith

5.4/10$3,120/yr more

Best OSS BSD-3 self-hostable, Cloud-and-self-host feature parity

Try FlagsmithSee Flagsmith alternatives

BSD-3 open-source core; SAML SSO at Scale-Up rather than Enterprise; bootstrapped indie since 2019.

PlanMonthlyAnnualWhat you get
FreeFree—50,000 API requests a month for one team member with unlimited flags, environments, and identity segmentation
Start-Up$45.00/mo$480.00/yr$45 a month monthly ($40 yearly) for 3 seats and 1 million API requests with A/B testing and scheduled flags
Scale-Up$300.00/mo$3,000.00/yr$300 a month monthly ($250 yearly) for 5 seats and 5 million-plus requests; adds SAML SSO, governance, and audit logs
EnterpriseCustomCustomCustom pricing with private cloud or self-hosted, real-time priority support, SLA, and onboarding

Flagsmith is the BSD-3 self-hostable pick and the catalog option with Cloud-and-self-host feature parity. Founded 2019 in Portsmouth UK by Ben Rometsch and Kyle Johnson (originally Bullet Train, rebranded 2020). Bootstrapped small-team. The wedge for OSS readers: most OSS flags vendors lock SAML SSO and audit log to enterprise self-host; Flagsmith offers Scale-Up tier features on both Cloud and self-host equivalently.

OSS self-host is BSD-3-licensed free forever for self-hosted deployment. Free Cloud is fifty thousand API requests monthly with one seat and unlimited flags, environments, and identity segments. Start-Up is the cheapest paid tier at forty-five dollars monthly with three seats, one million requests, A/B testing, and 2FA. Scale-Up at the upgrade tier covers five seats, five million requests, SAML SSO, governance roles, and audit logs. Enterprise covers private cloud and SLA at custom contract pricing.

The trade-off versus Unleash is OSS lineage; Flagsmith is newer than Unleash's 2014 origin. The trade-off versus GrowthBook is experimentation; Flagsmith ships basic A/B testing on Start-Up where GrowthBook ships warehouse-native experiments. For OSS readers who want SaaS UI plus the option to self-host with feature parity, Flagsmith is the right call.

Pros

  • BSD-3-licensed open-source core; Cloud-and-self-host feature parity
  • SAML SSO at Scale-Up rather than gated to Enterprise (useful for SOC 2 SMBs)
  • Free Cloud covers fifty thousand API requests monthly with unlimited flags
  • Bootstrapped indie since 2019 with no VC dilution risk
  • Self-hostable in private cloud at Enterprise with priority support and SLA

Cons

  • A/B testing on Start-Up is basic; pair with GrowthBook or Statsig for experimentation depth
  • Newer OSS lineage than Unleash (2019 vs 2014)
OSS BSD-3 free self-hostStart-Up $45/mo upgradeCloud-and-self-host parityOSS BSD-3 free forever; 7-day free trial Cloud

Best for: OSS readers who want SaaS UI plus the option to self-host with feature parity; SOC 2 SMBs needing SAML SSO below LaunchDarkly Enterprise scale.

Targeting
9
Rollout
8
DX
8
Value
8
Support
7
Try Flagsmith
#4

PostHog Feature Flags

5.1/10$720/yr more

Best OSS bundled with analytics, MIT platform with replay and experiments

Try PostHog Feature FlagsSee PostHog Feature Flags alternatives

MIT-licensed analytics platform with flags bundled in; YC W20; one platform for analytics, replay, and experiments.

PlanMonthlyAnnualWhat you get
FreeFree—1 million flag evaluations a month free, with the same product analytics, session replay, and experiments bundle as paid
Pay-as-you-go$100.00/mo$1,200.00/yrRoughly $100 a month for the realistic SMB at 2 million flag requests; bundled with the rest of the PostHog stack
Enterprise add-onCustomCustomCustom pricing from roughly $2,000 a month adding SAML SSO, audit logs, custom retention, and dedicated support for regulated teams

PostHog is the MIT analytics-bundled pick and the only catalog OSS option that bundles flags with broader product analytics on one platform. Founded 2020 in London by James Hawkins and Tim Glaser as a Y Combinator W20 batch. MIT-licensed open-source product analytics with flags, session replay, experiments, and surveys all on one usage-based bill. The wedge for OSS readers: one MIT OSS platform covers the entire product-data stack at zero per-product licensing cost.

OSS self-host is MIT-licensed free forever for self-hosted deployment with the full analytics, replay, experiments, and flags bundle. Cloud Free covers one million flag requests monthly with the same bundle. Pay-as-you-go above one million requests bills at small per-request rates. Enterprise add-on covers SAML SSO and audit logs at higher per-month pricing.

The trade-off versus Unleash is flags depth; PostHog flags are good but ship lighter approval flows and audit log than Unleash. The trade-off versus GrowthBook is warehouse-native posture; PostHog flags run on PostHog infrastructure where GrowthBook runs against the customer warehouse. For OSS readers who want one platform for the entire product-data stack, PostHog is the right call.

Pros

  • MIT-licensed OSS self-host free forever with the full analytics bundle
  • Only catalog OSS pick that bundles flags with analytics, replay, and experiments
  • Y Combinator W20; the most-recognized analytics-bundled OSS flags
  • Cloud Free covers one million flag requests monthly bundled with analytics
  • PAYG at small per-request rates above one million keeps SMB budgets predictable

Cons

  • Lighter approval flows and audit log than Unleash on free tier
  • Flags run on PostHog infrastructure where GrowthBook runs against customer warehouse
OSS MIT self-host freeCloud Free 1M req/moPAYG ~$100 at 2M reqOSS MIT free forever; Cloud Free 1M flag requests monthly

Best for: OSS readers who want one MIT platform covering the entire product-data stack (analytics, replay, experiments, flags) at zero per-product licensing.

Targeting
9
Rollout
8
DX
8
Value
9
Support
7
Try PostHog Feature Flags

How we picked

Each pick gets a transparent composite score from price, features, free-tier availability, and editor fit. Pricing flows from our live database, so when a vendor changes prices the score updates here too.

We weight price at 40 percent, features at 30, free tier at 15, fit at 15. Unleash leads because Apache 2.0 license plus around 12,000 GitHub stars plus the longest OSS lineage is the strongest community defensibility. See the parent /best/feature-flags guide for closed-source SaaS picks excluded from this lens.

We don't claim "30,000 hours of testing." Our methodology is the formula above plus the editor's published verdict for each pick. Verifiable, auditable, and updated when the underlying data changes.

Why trust Subrupt

We're a subscription tracker first, a buying guide second. Every claim on this page is something you can check.

By use case

Best OSS original Apache 2.0

Unleash

Read the full review →

Try Unleash

Best OSS warehouse-native MIT

GrowthBook

Read the full review →

Try GrowthBook

Best OSS BSD-3 Cloud parity

Flagsmith

Read the full review →

Try Flagsmith

Best OSS bundled with analytics

PostHog Feature Flags

Read the full review →

Try PostHog Feature Flags

How to choose your Open Source Feature Flags

License posture: Apache 2.0 vs MIT vs BSD-3

All four catalog OSS picks ship permissive licenses that allow all commercial use including SaaS resale at any revenue level. Unleash is Apache 2.0-licensed (the longest OSS lineage since 2014). GrowthBook and PostHog are MIT-licensed (the most permissive license commonly used in OSS). Flagsmith is BSD-3-licensed (similar to MIT in practical effect with explicit attribution requirements). License posture is uniform permissive across the OSS lens; agencies building white-label deployments and orgs of any revenue level are clear under all four. The decision pivots on architectural fit (flags-only with environment isolation versus warehouse-native experiments versus Cloud-and-self-host parity versus analytics-bundled) rather than license restrictions.

GitHub stars and community maturity

Community size is a proxy for plugin availability, documentation depth, and SDK breadth. Unleash leads at around 12,000 GitHub stars by 2026 with the longest OSS lineage since 2014. GrowthBook sits at around 7,000 stars with rapid growth on the warehouse-native marketing pitch. Flagsmith has around 5,000 stars with active community since 2019. PostHog has around 25,000 stars overall (analytics platform, not flags-specific). Out-of-catalog OSS projects worth knowing include Flipt (Go-based single-binary OSS at around 4,000 stars), GO Feature Flag (lightweight Go OSS), and OpenFeature (vendor-neutral spec). For maximum SDK breadth and community resources, Unleash is the safer pick. For warehouse-native compliance use cases, GrowthBook is the only fit.

Self-host operational tax across the four picks

Self-host is dollar-zero on licensing but readers pay infrastructure plus operational labor. Unleash self-host runs on a single VPS plus Postgres at around fifteen to thirty dollars monthly. GrowthBook self-host runs on similar VPS infrastructure plus the customer's existing warehouse for events. Flagsmith self-host runs on Postgres or MySQL on customer infrastructure. PostHog self-host is heavier because the platform bundles analytics ingestion at scale; expect a small Kubernetes cluster or dedicated VPS at fifty to one hundred dollars monthly. Production typically runs staging and prod, doubling the cost. For teams without DevOps capacity, Cloud upgrades trade operational labor for managed hosting at forty to seventy-five dollars per seat across the four picks.

Out-of-catalog OSS projects worth knowing

OSS feature-flags lists frequently include projects we do not yet catalog. Flipt is Go-based single-binary OSS with no external dependencies; competes with Unleash on operational simplicity for minimal-overhead deployments. GO Feature Flag is lightweight Go OSS with first-class CDN integration. OpenFeature is a CNCF vendor-neutral spec rather than a runtime; provides standard SDK interfaces that most OSS picks here support. From our catalog Unleash, GrowthBook, Flagsmith, and PostHog are the OSS feature-flags picks. Readers who specifically need Flipt (operational simplicity), GO Feature Flag (Go-stack performance), or OpenFeature (vendor neutrality) should evaluate those projects directly.

When to consider closed-source SaaS picks (cross-link to parent)

OSS self-host is the right path for teams that value auditable source code and accept the operational tax. Some teams have requirements that closed-source SaaS picks cover better. Brand reference for enterprise plus FedRAMP authorization is uniquely LaunchDarkly (closed-source SaaS). Experimentation-first design with multi-arm bandits and CUPED is Statsig (closed-source SaaS). Flat-rate unlimited-seats pricing is ConfigCat (closed-source SaaS). At any of those decision points, see [our /best/feature-flags guide](/best/feature-flags) for the closed-source picks excluded under the OSS lens.

Frequently asked questions

Why is Unleash ranked first over GrowthBook?

Unleash wins on community defensibility because Apache 2.0 license plus around 12,000 GitHub stars plus the longest OSS lineage since 2014 is the strongest community profile in catalog OSS feature-flags. GrowthBook wins on warehouse-native architecture specifically. Teams that want OSS lineage and broad SDK ecosystem pick Unleash. HIPAA, FedRAMP, or EU GDPR teams that need event data in their own warehouse pick GrowthBook. Both are auditable OSS at any revenue level.

Does Subrupt earn a commission from these OSS picks?

On a few. We disclose this on every /best page. Self-host OSS (Unleash, GrowthBook, Flagsmith, PostHog) has no affiliate path because there is no transaction. Cloud upgrades on all four have paid plans where we earn commission only on conversion. The composite ranking weights price at 40 percent, features at 30, free tier at 15, fit at 15; none tuned by affiliate rate.

Is BSD-3 really open-source like Apache 2.0 and MIT?

Yes. BSD-3 (the 3-clause BSD license that Flagsmith uses) is OSI-approved open-source like Apache 2.0 and MIT. All three are permissive licenses that allow commercial use, modification, and redistribution at any revenue level. The differences are minor: BSD-3 explicitly disallows using contributor names for endorsement without permission. For practical purposes, the four catalog OSS picks have uniform permissive license posture.

Should I run Unleash plus GrowthBook together?

Yes for some workflows. Unleash handles flags and rollouts as the primary tool; GrowthBook handles experiments against your warehouse. Many teams run both: Unleash for flags-with-environments daily workflow, GrowthBook for A/B test analysis against Snowflake or BigQuery data. Both are MIT or Apache 2.0 and both are genuinely free for self-host. The trade-off is operational complexity of running two services versus one.

How much does self-hosting actually cost in infrastructure?

A small Unleash, GrowthBook, or Flagsmith deployment runs on a single VPS plus Postgres at around fifteen to thirty dollars monthly. PostHog self-host is heavier because the platform bundles analytics ingestion; expect a small Kubernetes cluster at fifty to one hundred dollars monthly. Production typically runs staging and prod, doubling the cost. For teams without DevOps capacity, the Cloud upgrades trade operational labor for managed hosting.

Can I migrate from LaunchDarkly to OSS self-host?

Yes. LaunchDarkly exports flags as JSON via the API. Unleash imports JSON via custom migration scripts; GrowthBook imports via the management API; Flagsmith imports via CSV. Schema differences require remapping (LaunchDarkly variation IDs map to Unleash variants). Plan two to four weeks for a non-trivial migration with many flags and SDK updates. The honest framework: budget design time before starting; OSS self-host has different operational characteristics than managed SaaS.

EU data residency: which OSS picks store flag data in the EU?

All four OSS picks self-host gives full control of data residency. Unleash Cloud has multi-region with EU option. GrowthBook warehouse-native is uniquely EU-controllable because event data stays in your warehouse. Flagsmith Cloud has multi-region with EU. PostHog Cloud has multi-region with EU. For EU-resident OSS use, all four self-host paths plus Cloud EU regions qualify.

What about Flipt, GO Feature Flag, and OpenFeature?

Flipt is Go-based single-binary OSS with no external dependencies; competes with Unleash on operational simplicity. GO Feature Flag is lightweight Go OSS with first-class CDN integration. OpenFeature is a CNCF vendor-neutral spec rather than a runtime. None are in our catalog yet; from our catalog Unleash, GrowthBook, Flagsmith, and PostHog are the OSS picks. Readers who need Flipt or GO Feature Flag should evaluate directly.

How often is this guide updated?

We re-review pricing and feature changes annually at minimum, with mid-year refreshes when major vendor announcements happen. Unleash 2014 origin stable; Apache 2.0 license stable. GrowthBook MIT license and 7K stars rough as of 2026. Flagsmith BSD-3 license and Start-Up $45 stable. PostHog Y Combinator W20 origin stable. The lastReviewed date reflects the most recent editorial pass.

Subrupt Editorial

The team behind subrupt.com. We track subscriptions, surface cheaper alternatives, and publish buying guides where the score formula is on the page so you can recompute it yourself. We do not claim 30,000 hours of testing. What we claim is live pricing from our database, a transparent composite score, and honest savings math against a category baseline.

Last reviewed

Citations

Affiliate disclosure: Subrupt earns a commission when you switch to a service through our recommendation links. This never changes the price you pay. We only recommend services where there's a real cost or feature advantage for you, and our picks are based on the data on this page, not on which programs pay the most.

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