Auth0's bill grows with you. Keycloak's doesn't.

Auth0 operates on a subscription model that can be appealing for startups or small projects. Its free tier is generous on paper — up to 25,000 monthly active users (MAU) — but it's bounded on connections, organizations, and features, and most production workloads quickly outgrow it.

Here's the catch: Auth0's list prices look modest until you map them to how a real application actually uses the platform. As of 2026, Auth0's published pricing (per month, billed monthly) scales roughly like this:

Figures reflect Auth0's published list pricing as of 2026 (auth0.com/pricing); Auth0 changes pricing periodically — confirm current rates for your tier and region.

Two things push the real bill well beyond the headline numbers. First, the features you actually need live in higher tiers and add-ons — SAML and LDAP/Active Directory federation, log streaming, additional enterprise SSO connections (around $100/month each on B2B plans), metered M2M tokens, and the newer AI Agents add-on. Second, "users" and "organizations" aren't cheap: if you sell to businesses, Auth0's B2B model costs materially more than B2C at the same scale.

For anything beyond mid-size, Auth0 routes you into a custom Enterprise contract. In practice these negotiations tend to land in the six figures annually once SSO, MFA, organizations, and log streaming are bundled in. The problem isn't any single number — it's that the total is hard to predict and climbs with every feature and every user you add.

Keycloak, by contrast, is free to use regardless of users or scale. The primary cost is hosting and operating the software, which means your spend tends to be fixed — driven by infrastructure rather than user counts or feature gates.

Winner: Keycloak

Leveraging Phase Two's managed hosting keeps that spend predictable as you grow. See a side-by-side pricing estimate vs. Auth0.

As a managed service, Auth0 requires minimal maintenance from your side — it handles updates, security patches, and infrastructure.

Self-hosted Keycloak requires more attention: installation, configuration, upgrades, and the underlying infrastructure. Phase Two removes this trade-off entirely: with managed hosting and zero-downtime upgrades, you get Keycloak's control without the operational load.

Winner: Auth0 for self-hosted Keycloak — a tie when Keycloak is managed by Phase Two

Auth0 offers a broad set of authentication features out of the box — social logins, enterprise federation, database connections — and supports OAuth 2.0, OpenID Connect, and SAML. Customization happens through its Actions framework, which can become difficult to manage as logic grows outside the main application.

Keycloak matches Auth0 on core functionality and the same protocols, with customizable login, registration, and account-management UIs. Being open source, it lets developers extend the codebase far more freely — a higher ceiling for customization. A standout capability is Keycloak's on-premise deployment options.

Winner: Keycloak

The two are comparable on features, but Keycloak is far more extensible and configurable.

Choosing between Auth0 and Keycloak largely depends on your organization's needs. Auth0 is an excellent choice for teams that want a fully managed developer experience and are comfortable with per-MAU, per-feature costs. For organizations that prioritize cost savings and predictability, can manage their infrastructure, or require extensive customization, Keycloak emerges as a powerful, budget-friendly alternative.

Ultimately, we at Phase Two believe marrying the two together is the strongest match. We offer robust Keycloak hosting, migration, and support. Leveraging Keycloak means ongoing costs are relatively fixed, so concerns about user growth or feature needs don't have to factor into every decision.