head to head · open source
hydra vs cas
hydra has 17,553 GitHub stars, 1,609 forks, 98 open issues and last shipped 2 months ago. cas has 11,367 stars, 3,959 forks, 17 open issues and last shipped today. hydra leads on adoption by 54% (17,553 vs 11,367 stars). hydra is written in Go under Apache-2.0; cas is written in Java under Apache-2.0. hydra has attracted 9% as many forks as stars, cas 35%. cas was the more recently maintained of the two, and both are self-hostable with no licence fee. The two share 2 topic tags (authorization, oauth2), so they are genuine substitutes rather than adjacent tools.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| hydra | cas | |
|---|---|---|
| GitHub stars | ★ 18K | ★ 11K |
| License | Apache-2.0 | Apache-2.0 |
| Written in | Go | Java |
| Last push | 2026-07-29 | 2026-09-20 |
| Forks | ⑂ 1.6K | ⑂ 4.0K |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick hydra if
- You weight community size — 18K stars and counting
- You want the Apache-2.0 license terms
- Your stack matches Go
- You value the larger contributor base for long-term maintenance
pick cas if
- You want the cas feature set and don't need the biggest community
- You prefer the Apache-2.0 license terms
- Your stack matches Java
- You evaluated both and cas fits your workflow better
About hydra
Ory Hydra is an OpenID Certified OpenID Connect and OAuth 2.1 provider written in Go and licensed under Apache 2.0, built for teams that need standards compliant token issuance, client management, and consent flows while user accounts stay in their own existing identity system.
read the full hydra overview →
About cas
Apereo CAS is the open source Java server that implements the Central Authentication Service protocol and serves as an enterprise identity provider and single sign on platform for the web, aimed at organizations that need one authentication and authorization layer across many applications.
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Frequently asked questions
Is hydra or cas more popular?
hydra has 17,553 GitHub stars and cas has 11,367. hydra has the larger community by that measure.
Are hydra and cas free?
Both are open source. hydra is licensed under Apache-2.0 and cas under Apache-2.0. Neither carries a licence fee.
What is the difference between hydra and cas?
hydra is written in Go and cas in Java. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, hydra or cas?
Choose hydra if you want the larger community (17,553 stars) or its Apache-2.0 licence terms. Choose cas if its feature set, stack or Apache-2.0 licence fits better. Both are self-hostable.