# Open Source vs. Paid

ALTCHA has one free, open-source core, and two paid ways to run more on top of it — **Cloud** (we host it) and **Sentinel** (you host it). All three block bots using the same proof-of-work engine underneath; the paid plans add a layer that decides *when* to ask more of a visitor. See [How ALTCHA Works](/docs/how-it-works/) for that concept in more detail.

## The one-sentence version

- **Open-source** — free forever, you run it, the same invisible check for every visitor.
- **Cloud** — adds adaptive, risk-based protection, fully managed by us.
- **Sentinel** — everything in Cloud, plus more of the platform, running on your own infrastructure.

## What's free forever

The [open-source widget and libraries](/open-source-captcha/) include, at no cost and with no sign-up:

- No cookies or tracking
- GDPR & CCPA compliant
- WCAG 2.2 AA accessible
- Proof-of-work verification
- Self-hosted, with full data ownership
- MIT licensed — use it however you like

This is a complete, production-ready CAPTCHA replacement on its own. See [Quick Start](/docs/integration/quick-start/) to add it to your forms.

## What Cloud adds

On top of the open-source core, [Cloud](/docs/cloud/) adds adaptive protection, fully managed by us on EU servers — no setup, no maintenance, live in minutes:

- Adaptive, risk-based challenges (only ask more from visitors who look suspicious)
- Real-time threat intelligence
- A hosted dashboard with analytics

## What Sentinel adds

[Sentinel](/docs/sentinel/) includes everything in Cloud, plus additional platform features exposed via its API — such as the [Classifier](/docs/sentinel/features/classifier/) — since it runs the full engine rather than a subset of it. Sentinel runs on your own infrastructure, giving you full data sovereignty, with the option to run entirely air-gapped.

You can move between the open-source core, Cloud, and Sentinel later without changing your widget integration — see [Pricing](/pricing/) for exact plans and rates.

## Which one should I choose?

- **Just getting started, or want it free forever** → the open-source widget.
- **Want it managed, with no server to run yourself** → Cloud.
- **Need full control over your infrastructure and data** (compliance, air-gapped environments, etc.) → Sentinel.

For a more detailed breakdown by use case, see [Solutions](/docs/solutions/).

## Next steps

- **[Quick Start](/docs/integration/quick-start/)** — add the open-source widget to your forms
- **[Cloud](/docs/cloud/)** — get started with the managed service
- **[Sentinel](/docs/sentinel/)** — self-host the full platform
- **[Pricing](/pricing/)** — compare plans and pricing