What changed in Bazel from 8 to 9

[!NOTE] If you are looking for rolling releases, please visit this page.

Release 9.2.0 (2026-07-13)

Bazel 9.2.0 is a minor LTS release. It is fully backward compatible with Bazel 9 releases starting from 9.0.1; see Bazel 9.0.1 release notes for a note on backward compatibility.

Configurability

• The new refines_constraint_value attribute on constraint_setting can be used to indicate that any non-default value for that setting specified on a platform requires the refined value to also be specified. (#29727)
• Bazel no longer crashes when a label_list_dict attribute is used in a split transition (#29830). (#29856)
• exec_properties now respects resources:cpu and resources:memory for local resource estimation. (#29426)
• The and_then method on transitions can be used to compose transitions. Both Starlark transitions and native transitions (e.g. config.exec()) are supported. (#29888)

Core

• Source directories in external repositories are temporarily allowed to cross package boundaries. This will be disallowed in the future, gated by the new --incompatible_check_external_repo_source_dir_package_boundary flag. (#30040)

External Deps

• Added SOCKS proxy support. Bazel now accepts socks://, socks4://, and socks5:// URLs in HTTPS_PROXY/HTTP_PROXY environment variables and related system properties. (#29364)
• Adds the strip_components attribute to extract/download_and_extract/http_archive to allow stripping of path components when extracting files. (#29369)
• Added the module_ctx.tag_sort_key(tag) method, which returns an opaque object for the given tag that can be compared to derive the order in which tags from different classes appear in the MODULE.bazel file. (#29484)
• module_extension(...) now accepts a facts_version integer parameter. Bumping it invalidates the facts persisted in MODULE.bazel.lock for that extension, allowing extension authors to make breaking changes to the facts schema without risking misinterpretation by older code paths. (#29871)
• External repos are no longer refetched whenever they contribute inputs to an action using the hermetic Linux sandbox. (#29889)
• The remote repo contents cache now correctly materializes chains of symlinks as action inputs, but no longer supports symlinks into the main repository. (#29959)
• Fixed spurious "No such file" errors with the remote repo contents cache when a repo contains a symlink to a .bzl file. (#30037)
• The remote repo contents cache no longer caches or restores repos with cross-repo symlinks, thus avoiding a large surface area for bugs. The effort to reenable this support is tracked by #30160. (#30190)
• Modifying environment variables no longer causes spurious reloading of packages in external repositories. (#30194)

Performance

• Fixed a performance regression in Bazel 9 that causes RepoMappingManifest actions to consume a lot of CPU time. (#29807)

Remote Execution

• Enable TCP keepalive by default for gRPC connections with reasonable defaults (#29898)
• Fixed repo content caching for non-gRPC cache backends. (#29869)
• CDC chunk uploads and downloads can now happen in parallel within a large blob. (#29796)
• Bazel no longer limits the size of gRPC messages received from the remote executor or cache. (#29885)
• Fixed a crash with --experimental_remote_repo_contents_cache when running without a remote or disk cache. (#30060)
• Fixed a spurious remote-execution failure with --experimental_output_paths=strip where a lost input in a tree artifact shared between actions could not be recovered by action rewinding. (#30193)

Starlark / Build Language

• Created --incompatible_remove_ctx_android_fragment for Starlark Flags migration (#29884)

Windows

• Fixed Bazel being unable to run a Windows executable whose path is too long to shorten under MAX_PATH, e.g. when 8dot3 short names are disabled (microsoft/Windows-Containers#507). (#29984)
• Windows launcher stubs now embed an asInvoker UAC manifest, preventing "The requested operation requires elevation. (error: 740)" for targets whose name matches the installer-detection heuristic. (#30182)

Acknowledgments

This release contains contributions from many people at Google, as well as Ashutosh0x, Bryce Lampe, Fabian Meumertzheim, Fredrik Medley, gaurav0107, Grzegorz Lukasik, Jacob Nowjack, John Cater, JonathanPerry651, Keith Smiley, peakschris, Rgis Desgroppes, Richard Lavoie, Sarad, Son Luong Ngoc, Tamir Duberstein, Tyler French, vadim, Will Stranton, and Yonatan Goldschmidt.

Notice: Bazel installers contain binaries licensed under the GPLv2 with Classpath exception. Those installers should always be redistributed along with the source code.

Some versions of Bazel contain a bundled version of OpenJDK. The license of the bundled OpenJDK and other open-source components can be displayed by running the command bazel license. The vendor and version information of the bundled OpenJDK can be displayed by running the command bazel info java-runtime. The binaries and source-code of the bundled OpenJDK can be downloaded from our mirror server.

Security: All our binaries are signed with our public key 3D5919B448457EE0.

[!NOTE] If you are looking for rolling releases, please visit this page.

Release 9.1.1 (2026-06-03)

Bazel 9.1.1 is a patch LTS release. With the exception of CcInfo (see below), it is backward compatible with Bazel 9.0.

IMPORTANT

Compatibility Note: CcInfo removal and rules_go

If you encounter the error "The CcInfo symbol has been removed", this is due to an intentional change in Bazel 9 regarding C++ Starlarkification. While this change was present in 9.0.0, a bug fixed in 9.0.1 (#28360) now correctly surfaces this error instead of failing silently or with a confusing message. To fix this, please upgrade rules_go, rules_nodejs or any broken rulesets. For example,

# Add repo_name = None if you don't directly depend on them.
bazel_dep(name = "rules_go", version = "0.59.0") 
bazel_dep(name = "rules_nodejs", version = "6.7.3")

External Deps

• --downloader_config was accidentally made a repeatable flag in 9.1.0, which was a backwards-incompatible change. This has been reverted in 9.1.1. (#29616)
• Fixed a crash with file:// URIs. (#29579)
• Fixed a crash with opaque URIs. (#29658)

Remote Execution

• Fixed an issue that caused Bazel to fail on a lost input even with build or action rewinding enabled. (#29677)
• Fix crash on --remote_default_exec_properties with the same key. (#29596)
• Verify the whole blob when downloading chunks (#29593)
• Support bounded parallel chunk transfers (#29614)
• Fix JVM crash from VerifyException in GrpcCacheClient.onNext() (#29583)
• Invalidate unresolved symlink info after deletion in the RAFS (#29671)

Acknowledgments

This release contains contributions from many people at Google, as well as Armando Montanez, ashutosh0x, Boleyn Su, Fabian Meumertzheim, H5-O5, Joseph Gette, Keith Smiley, Paul Tarjan, Ted Kaplan, Tyler French, and Will Stranton.

Notice: Bazel installers contain binaries licensed under the GPLv2 with Classpath exception. Those installers should always be redistributed along with the source code.

Some versions of Bazel contain a bundled version of OpenJDK. The license of the bundled OpenJDK and other open-source components can be displayed by running the command bazel license. The vendor and version information of the bundled OpenJDK can be displayed by running the command bazel info java-runtime. The binaries and source-code of the bundled OpenJDK can be downloaded from our mirror server.

Security: All our binaries are signed with our public key 3D5919B448457EE0.

[!NOTE] If you are looking for rolling releases, please visit this page.

Release 9.1.0 (2026-04-20)

Bazel 9.1.0 is a minor LTS release. With two exceptions (see below: CcInfo and --downloader_config), it is backward compatible with Bazel 9.0 and contains selected changes by the Bazel community and Google engineers.

IMPORTANT

Compatibility Note: CcInfo removal and rules_go

If you encounter the error "The CcInfo symbol has been removed", this is due to an intentional change in Bazel 9 regarding C++ Starlarkification. While this change was present in 9.0.0, a bug fixed in 9.0.1 (#28360) now correctly surfaces this error instead of failing silently or with a confusing message. To fix this, please upgrade rules_go, rules_nodejs or any broken rulesets. For example,

# Add repo_name = None if you don't directly depend on them.
bazel_dep(name = "rules_go", version = "0.59.0") 
bazel_dep(name = "rules_nodejs", version = "6.7.3")

CLI

• Reporting of cached test results can now be suppressed with --test_summary=short_uncached or --test_summary=detailed_uncached. (#29263)

Configurability

• Fix launcher/launcher_maker for cross build, e.g. build windows binary on linux machine. (#29239)

External Deps

• The --downloader_config flag can now be specified multiple times to use several downloader config files at once. Note that this is technically a breaking change, and will be reverted in future 9.x releases, starting from 9.1.1. Bazel 10.x will again contain this incompatible change.
• The compatibility_level and max_compatibility_level attributes of module in MODULE.bazel are now no-ops. Module maintainers should stop specifying those attributes and provide clear build time error messages and actionable migration paths when making major breaking changes. (#28616)
• package_group now supports labels with external repositories in the packages attribute. (#28893)
• rctx.symlink now implicitly watches the target if it falls back to a copy. (#28741)
• The local and remote repo contents cache now include the host OS and CPU architecture in the cache key. (#29195)
• The remote repo contents cache now supports all reproducible repo rules. (#29225)

Remote Execution

• Bazel now has experimental support for --rewind_lost_inputs, which can rerun actions within a single build to recover from (remote or disk) cache evictions. (#28958)
• Added --experimental_remote_cache_chunking flag to read and write large blobs to/from the remote cache in chunks. Requires server support. (#28903)

Starlark / Build Language

• string.splitlines() no longer incorrectly treats u+0085 (NEL) as a newline character (#28931)

Acknowledgments

This release contains contributions from many people at Google, as well as Armando Montanez, ashutosh0x, Boleyn Su, Fabian Meumertzheim, H5-O5, Joseph Gette, Keith Smiley, Paul Tarjan, Ted Kaplan, Tyler French, and Will Stranton.

Notice: Bazel installers contain binaries licensed under the GPLv2 with Classpath exception. Those installers should always be redistributed along with the source code.

Some versions of Bazel contain a bundled version of OpenJDK. The license of the bundled OpenJDK and other open-source components can be displayed by running the command bazel license. The vendor and version information of the bundled OpenJDK can be displayed by running the command bazel info java-runtime. The binaries and source-code of the bundled OpenJDK can be downloaded from our mirror server.

Security: All our binaries are signed with our public key 3D5919B448457EE0.