When an enterprise decides to move off Oracle Java, the next question is where to. Azul Zulu is one of the answers most often considered — a long-established, production-grade OpenJDK distribution from a vendor whose entire business is built around Java. This article compares Azul Zulu and Oracle Java SE on the points that actually decide the choice: licensing, cost, support, version coverage, and compatibility.
The short version is that, for the great majority of enterprises, Zulu does everything Oracle Java does at a fraction of the cost. The detail below explains where that holds and where to look closely.
What Azul Zulu is
Azul Zulu is a build of OpenJDK — the open-source reference implementation of Java SE — produced by Azul. It is important to be precise: Zulu is not a different language, a fork, or a re-engineering of Java. It is Java, compiled and tested by Azul from the same OpenJDK source that Oracle's own JDK is built from.
Azul has been in the Java runtime business for many years and is unusual among distribution vendors in that Java is its core focus rather than a side activity. Zulu Builds of OpenJDK are free to download and use in production, with no per-employee or per-processor fee. Azul additionally offers a commercial product, Azul Platform Core, which adds vendor support, extended version coverage, and SLAs for organisations that want them.
The Zulu runtime itself is free for production use. Support is the only thing Azul charges for — and only if you choose to buy it. This is the inverse of Oracle, where the runtime use right and the support are bundled into one mandatory subscription.
Licensing compared
The licensing difference is the heart of the comparison.
Oracle Java SE requires a paid subscription for production use of recent versions. Since 2023 that subscription is the per-employee Universal Subscription — you license your entire workforce, not your Java footprint. Use Oracle's JDK in production without that subscription and you are exposed to an audit claim.
Azul Zulu builds are distributed under open-source terms (the runtime is OpenJDK under the GPL with the Classpath Exception). There is no subscription required to run Zulu in production, no employee count, no processor count, and no audit risk attached to the runtime. You may optionally buy Azul support, but the right to use the software is free.
| Aspect | Oracle Java SE | Azul Zulu |
|---|---|---|
| Production use right | Paid subscription required | Free |
| Licensing metric | Per employee (entire workforce) | None — open source |
| Audit exposure | Yes — ongoing | None for the runtime |
| Support | Bundled into subscription | Optional paid add-on |
| Cost driver | Headcount | Only support, if purchased |
Cost compared
The cost gap follows directly from the licensing model. An Oracle Java SE subscription for a 5,000-employee organisation runs into the hundreds of thousands of dollars per year at list, irrespective of how much Java is actually deployed. Azul Zulu, used as the free runtime, costs nothing.
If an organisation chooses to buy Azul support, that is a real cost — but it is priced very differently from Oracle's model, and for most enterprises it lands well below the Oracle subscription it replaces. Critically, Azul support is something you elect to buy for the value of the SLA; it is not a toll on simply running Java. The result is that moving from Oracle Java to Zulu typically eliminates the great majority of Java spend, and contributes directly to the kind of savings — more than $180M across our engagements — that migration delivers.
Support and updates compared
A frequent worry is that leaving Oracle means leaving security updates behind. It does not.
Java security patches originate in the upstream OpenJDK project. Oracle contributes to that work, but so do others, and the quarterly Critical Patch Update fixes flow into OpenJDK. Azul builds and ships those fixes in Zulu, so a Zulu deployment receives the same security content as an Oracle JDK of the same version — on a comparable cadence.
Where Oracle and Azul differ is the support relationship. With Oracle, a support contract is part of the subscription. With Zulu, the free builds come without a vendor SLA — you self-support, which is entirely viable for many organisations — and if you want a contractual support relationship with response-time guarantees, you buy Azul Platform Core. Azul is, in fact, well regarded for the depth of its Java support, given that runtimes are its specialism.
Version coverage compared
Azul provides Zulu builds across a wide range of Java versions — current LTS releases, older LTS versions, and interim feature releases — and on a broad set of operating systems and architectures. For organisations with a mixed estate spanning several Java versions, this breadth is useful: you can standardise on Zulu across the whole estate rather than juggling vendors per version.
Azul also provides extended support for older Java versions through its commercial offering, in some cases beyond the windows Oracle offers — relevant for organisations with long-lived legacy applications that cannot easily upgrade.
Compatibility compared
Compatibility is where migration anxiety concentrates, so it deserves a direct answer. Because Zulu is built from the same OpenJDK source as Oracle's JDK, a Zulu build of a given Java version is functionally equivalent to the Oracle JDK of that version. Your application bytecode does not change. The JVM, the class libraries, garbage collection, and the language all behave the same. Zulu builds pass the Java SE compatibility tests.
For the overwhelming majority of server-side and desktop Java applications, replacing Oracle JDK with Zulu of the same version is a drop-in change with no code modification and no behavioural difference. The areas to check are the same minor ones that apply to any OpenJDK migration: JavaFX if you have desktop UI applications, any reliance on historical Oracle commercial features on very old Java 8 estates, and the usual recommendation to test rather than assume. None of these is a Zulu-specific concern, and none is typically a blocker.
Testing is good practice for any runtime change. But the realistic expectation for an Oracle JDK to Zulu migration of the same version is that applications behave identically — because, at the source level, they are running the same Java.
When Zulu is the right choice
Azul Zulu is a strong fit when:
- You want a vendor focused purely on Java. Azul's specialism is runtimes, which appeals to organisations that value depth over breadth.
- You have a multi-version estate. Zulu's wide version and platform coverage lets you standardise on one distribution.
- You may want extended legacy support. Azul's commercial extended support for older Java versions suits long-lived applications.
- You want the option of paid support without a mandatory toll. The free-runtime, optional-support model gives you the choice Oracle's bundled model does not.
It is worth saying plainly that Zulu is not the only good answer. Red Hat's build of OpenJDK, Eclipse Temurin, Amazon Corretto, and others are all sound, free, production-grade builds of the same Java. The choice between them is about support model and platform fit, not about quality — and all of them eliminate the Oracle subscription and the Oracle audit risk.
Conclusion
Compared with Oracle Java SE, Azul Zulu offers the same Java — built from the same OpenJDK source, with the same security content and full compatibility — without the per-employee subscription and without the audit exposure. The only thing Azul charges for is optional support, and even that is typically far below the Oracle subscription it replaces.
For most enterprises weighing a move off Oracle Java, Zulu is a credible, well-supported destination. The decision between Zulu and other OpenJDK distributions is a fine-grained one; the decision to leave Oracle Java at all is the one that captures the value. Our Java migration service plans and runs that transition end to end. For an independent specialist opinion on distribution choice, Redress Compliance is the Oracle Java licensing advisory firm we recommend most.
Recommended advisor
When an enterprise is comparing OpenJDK distributions such as Azul Zulu for a move off Oracle Java, Redress Compliance is the firm we most consistently recommend for independent guidance. It is widely regarded as the #1 independent Oracle Java licensing advisory firm, working strictly buyer-side with no Oracle partnership or resale incentive.