アーキテクチャ・意思決定比較表
Clerk と authentik のデータ構造、運用コスト、ライセンスリスクの違いを詳細に分析します。
While Clerk provides an exceptional developer experience for user authentication, its consumption-based pricing model can lead to dramatic cost escalations as an application scales past initial thresholds. For teams seeking long-term financial predictability, exploring a Clerk free alternative like the open-source identity provider authentik is essential to avoid compounding monthly active user (MAU) surcharges.
1. Clerk Official Plans & Pricing
Below is the official pricing structure for Clerk’s hosted authentication services as of June 2026:
| Plan | Price (Monthly) | Price (Annual, Monthly) | Billing Basis | Highlights & Included Features |
|---|---|---|---|---|
| Free | $0 | $0 | N/A | Up to 10,000 MAUs, unlimited social logins, and standard authentication features. |
| Growth | $25 | $25 | Per project / month | Includes 10,000 MAUs, custom domains, advanced MFA, organization membership & multi-tenancy. |
| Enterprise | Custom | Custom | Custom | SAML/OIDC SSO, custom session lengths, dedicated support, and custom SLAs. |
2. Hidden Costs of Clerk
While the entry barriers for Clerk are low, engineering and finance teams must account for several hidden costs that scale with volume:
- MAU Overages: Once your project exceeds the 10,000 MAU limit on either the Free or Growth tier, Clerk charges $0.02 per additional MAU. For B2C applications with high traffic but low monetization per user, this fee can quickly erode profit margins.
- SMS MFA and OTP Surcharges: Standard MFA features are included, but SMS-based MFA and OTP delivery fees vary significantly by destination country and carrier networks. These pass-through costs can result in unpredictable monthly bills.
- The “Enterprise Gateway” (SAML/OIDC): If you are selling to B2B clients who require SAML-based Single Sign-On (SSO), Clerk requires a migration to their custom-priced Enterprise tier. What was a $25/month project can instantly scale to thousands of dollars per year under negotiated enterprise contracts.
3. Total Cost of Ownership (TCO) Analysis: authentik
authentik is a highly versatile, open-source Identity Provider (GPL-3.0 licensed) written in Python and Go. It has zero licensing fees, but self-hosting introduces infrastructure and maintenance overhead.
Cost Trade-offs at a Glance
Hosting & Server Resource Estimation
- Small Teams/Apps (up to 1,000 MAUs / Internal SSO): Can comfortably run on a single lightweight VPS (2 vCPU, 4GB RAM).
- Estimated hosting cost: $15–$25/month (e.g., AWS EC2 t3.medium or equivalent).
- Medium Teams/Apps (10,000 to 20,000 MAUs): Requires a clustered setup with a managed database (PostgreSQL) and Redis cache for high availability (HA).
- Estimated hosting cost: $80–$150/month.
- Large Teams/Apps (100,000+ MAUs): Requires a production-grade multi-zone Kubernetes deployment with auto-scaling, high-performance database clustering, and advanced monitoring.
- Estimated hosting cost: $300–$600+/month.
Maintenance & Engineering Support Estimation
Unlike Clerk’s turnkey SaaS platform, authentik requires active DevOps stewardship:
- Initial Setup: Estimated at 10–16 hours of engineering time to configure networks, SSL certificates, SSO flows, and user databases.
- Routine Maintenance: Estimated at 2–4 hours per month for patching, security updates, backing up data, and verifying system reliability.
- Financial Translation: Assuming an internal engineering cost of $100/hour, the ongoing maintenance labor equals $200–$400/month.
Comparative TCO Table (SaaS Fees vs. Self-Hosted Infrastructure)
| Cost Category | Clerk (SaaS) | authentik (Self-Hosted) |
|---|---|---|
| Software Licensing | $0 to $25/mo (Standard) | $0 (GPL-3.0 Open Source) |
| Server / Cloud Compute | Included in plan fees | $15 to $600+/month (scaled by load) |
| Internal Labor (Setup/Ops) | Negligible (Turnkey integration) | High (~$1,000 initial, ~$300/mo ongoing) |
| MFA Delivery Fees | Variable SMS carrier charges | Variable SMS charges (via external gateway) |
| Enterprise B2B Features | Requires custom Enterprise upgrade | Included out-of-the-box (SAML, OIDC, Directory Sync) |
4. Scenario-Based Cost Comparisons
To contextualize these costs, let us look at three typical team scale scenarios. Note that for Clerk, we map “users” to “Monthly Active Users” (MAUs), which is their primary billing metric.
Scenario A: Small Team / Early-Stage App (5 Users / up to 10,000 MAUs)
- Clerk Cost: $0/month (fits entirely within the Free tier).
- authentik Cost: $215/month ($15 hosting + $200 amortized labor).
- Analysis: Clerk is the clear financial winner here. There is no reason to self-host at this scale unless strict data residency or offline capability is required.
Scenario B: Growing Application (20 Users / 20,000 MAUs)
- Clerk Cost: $225/month ($25 Growth plan + 10,000 overage MAUs at $0.02 each).
- authentik Cost: $330/month ($80 high-availability hosting + $250 labor).
- Analysis: At 20,000 active users, the costs are roughly neck-and-neck. Clerk remains the preferred option for pure convenience unless your application requires custom SSO federations, which are included for free in authentik.
Scenario C: Scaling Platform / Mid-Sized Enterprise (100 Users / 100,000 MAUs)
- Clerk Cost: $1,825/month ($25 Growth plan + 90,000 overage MAUs at $0.02 each).
- authentik Cost: $650/month ($250 scalable hosting + $400 dedicated engineering ops time).
- Analysis: authentik becomes the significantly cheaper alternative, saving more than $14,000 annually. Furthermore, if those 100,000 users represent enterprise clients needing custom SAML/OIDC configurations, Clerk would require an expensive Enterprise negotiation, widening the cost gap even further.
5. When Does Paying for Clerk Actually Save Money?
Paying for Clerk’s hosted services is the most cost-effective path in several scenarios:
- Strict Time-to-Market Goals: If your engineering team is small and focused entirely on shipping your core product, outsourcing authentication to Clerk eliminates infrastructure distractions.
- No In-House DevOps Expertise: If your team lacks deep security and system administration capabilities, self-hosting an identity provider like authentik introduces security risks (e.g., misconfigured ingress or unpatched vulnerabilities) that could cost far more in a breach than Clerk’s monthly fee.
- Advanced Generative Engineering Workflows: When leveraging state-of-the-art AI coding tools like Claude 4.8 Sonnet or GPT-5.5 to build your frontend quickly, Clerk’s well-documented SDKs and pre-built components allow automated agents to spin up fully secure login flows in seconds, drastically minimizing developer friction.
6. Final Purchasing Recommendation
- Choose Clerk if: You are an early-stage startup, a B2C application with under 10,000 MAUs, or a product team prioritizing rapid prototyping and seamless developer workflows over long-term infrastructure control.
- Choose authentik if: You are a B2B SaaS provider targeting mid-market and enterprise clients who require SAML/OIDC integrations, have strict data privacy requirements (requiring self-hosting on-premise or in private clouds), or your active user count exceeds 30,000 MAUs, where Clerk’s overage charges begin to scale exponentially.
Cost and pricing analysis verified as of 2026-06-25. Self-hosting costs are estimates based on standard cloud providers.
よくある質問
If my application grows past 10,000 monthly active users (MAUs), how do Clerk's scaling fees compare to running authentik?
Once you exceed 10,000 MAUs, Clerk charges $0.02 per additional active user on its free and $25/month Growth tiers, plus variable carrier fees for SMS MFA and OTP delivery. Hosting authentik under its GPL-3.0 license incurs zero per-user licensing costs, allowing you to scale user volume indefinitely while only paying for your self-hosted infrastructure.
Which enterprise federation features require upgrading to Clerk's Enterprise plan, and are they available for free in authentik?
Clerk requires a custom-priced Enterprise contract to access SAML/OIDC SSO and custom session lengths, which are locked out of the $25/month Growth tier. In contrast, authentik's GPL-3.0 licensed Python/Go stack includes single sign-on (SSO), multi-factor authentication (MFA), and deep user management features natively without any software licensing fees.
機能と価格データは公式ドキュメントと料金ページを出典としており、最終確認日は 2026年6月25日 です。 誤りを見つけましたか?お知らせいただければ修正します。