This is a 13-million-line platform, not a Java installer
The OpenJDK checkout we measured contains the HotSpot virtual machine, Java libraries, compilers, launchers, serviceability tools, and native platform code in one source tree. That scope explains why the repository is useful to JDK implementers and excessive for ordinary Java development. An application team needs a supported binary. A platform team may need to change garbage collection, add an intrinsic, revise a class-library API, or validate a port across the VM and libraries together.
The README is only 429 bytes because it points directly to the build manual, the OpenJDK community site, and the separate JDK bug tracker. That is terse but honest. The real documentation assumes its reader is building a platform: it covers bootstrapping, native compilers, external libraries, cross compilation, build variants, generated images, and test selection. Reading that manual before cloning saves more time than any abbreviated third-party recipe.
An x86 build asks for at least 6 GB free
The official build guide advises 2 to 4 cores, 2 to 4 GB of RAM, and at least 6 GB of free disk for x86. AArch64 guidance starts higher at 8 cores and 8 GB of RAM. The project strongly recommends an SSD because the build is disk intensive. Those are entry conditions, not performance promises, and broader configurations or repeated builds can require more.
Bootstrapping is the first unusual requirement. Building major JDK version N generally needs a suitable JDK from an earlier release, with the guide describing an N minus 1 rule of thumb and exceptions early in a release cycle. The build also needs a supported C or C++ toolchain, GNU Make, Bash, and system libraries such as FreeType, fontconfig, CUPS, X11, or ALSA depending on the platform. configure checks these inputs before compilation.
What happened when we ran it
Our sandbox cloned commit f40a2c3 into an unprivileged container with 3 CPUs and 8 GB of RAM. The checkout was 694 MB, with 70,924 files and about 13,055,178 lines of source. The install phase attempted to execute ./configure and failed after 5 seconds with exit 126. The complete diagnostic supplied at the end was ./configure: Permission denied.
That failure happened before configuration, compilation, or testing. We therefore have no build duration, package count, test count, or audit result for this repository, and we will not manufacture one. The documented command is bash configure, followed by make images; our generic runner used direct execution instead. That difference identifies where the harness stopped, but it does not prove why the file lacked executable permission in that checkout.
The repository has 7 CI workflow files and a test directory. Neither signal changes our result: our run did not reach them. A proper contributor check begins by producing a configured JDK image, then uses the test targets relevant to the change. The 5-second permission error is a setup finding, not a verdict on HotSpot or Java test health.
Tier 1 is the minimum contributor test
OpenJDK's testing guide makes make test-tier1 the basic local target. Contributors are expected to test the changed area and run at least tier 1. Higher tiers add broader, slower, less stable, specially configured, or GUI-dependent cases. The common interface can dispatch jtreg suites, HotSpot gtest, JMH microbenchmarks, and a few special test families. There is no useful single count to quote without naming a configuration and selection.
Windows adds another layer. Microsoft Visual Studio supplies the native compiler, but the build also requires a POSIX environment. Cygwin, MSYS2, and both WSL generations are supported, with the guide describing Cygwin as the most tested path. WSL can target Windows or Linux, but the boot JDK and source location must match the target's accessibility. Testing under WSL is described as not fully functional, a real reason to avoid choosing it blindly for contributor work.
410 GitHub items are only part of project health
The repository was pushed on August 26, 2026, and GitHub reported 416 open issues and pull requests combined. The current activity we fetched included work on Vector API behavior, value objects, garbage collection, cryptographic intrinsics, desktop integration, and platform tests. Most user-visible bug tracking lives at bugs.openjdk.org, so the GitHub count should not be mistaken for the full JDK defect backlog.
GitHub's latest-release endpoint returned no release for this repository. That is not abandonment evidence. OpenJDK uses its own release processes and distribution ecosystem, while same-day mainline changes show active development. Judge this tree as a platform source project: it has demanding prerequisites, precise build documentation, and layered tests. For users, choose a vendor binary. For JDK engineers, few substitutes offer the same direct path into Java's reference open-source implementation.