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Version: 2.9.x(Latest)

Go 1.25 (2025-08-12)

Go 1.25 brings significant improvements to the toolchain, runtime, and standard library, while maintaining Go 1 compatibility.

Language Changes​

Go 1.25 introduces no language-level changes affecting Go programs. However, the concept of core types has been removed from the language specification in favor of descriptive prose.

Toolchain​

Go Command​

  • ASan Leak Detection: The go build -asan option now defaults to detecting memory leaks at program exit. Memory allocated by C that is not freed and not referenced by other memory will be reported as an error. Disable this feature by setting ASAN_OPTIONS=detect_leaks=0.

  • Optimized Tool Dependencies: The Go distribution now includes fewer prebuilt tool binaries. Core toolchain binaries like the compiler and linker remain included, but other tools are built on demand by go tool.

  • ignore Directive: The new ignore directive in go.mod specifies directories that the go command should ignore. Files in these directories are excluded during package matching but included in module zip files.

  • Enhanced go doc: The go doc -http option starts a documentation server and opens it in a browser window.

  • Improved go version: The go version -m -json option outputs JSON-encoded runtime/debug.BuildInfo structures embedded in Go binaries.

  • Module Subdirectory Support: The go command now supports using repository subdirectories as module root paths with <meta name="go-import" content="root-path vcs repo-url subdir"> syntax.

  • work Package Pattern: A new work package pattern matches all packages in the work module(s).

  • Toolchain Line Removal: The go command no longer adds a toolchain line when updating the go line in go.mod or go.work.

Vet Tool​

New analyzers:

  • waitgroup: Reports misplaced calls to sync.WaitGroup.Add.
  • hostport: Reports uses of fmt.Sprintf("%s:%d", host, port) for constructing addresses for net.Dial, suggesting net.JoinHostPort instead.

Runtime​

Container-Aware GOMAXPROCS​

  • Linux cgroup Awareness: On Linux, the runtime considers the CPU bandwidth limit of the cgroup containing the process. If the limit is lower than the number of logical CPUs, GOMAXPROCS defaults to the lower limit.

  • Dynamic Updates: The runtime periodically updates GOMAXPROCS when the number of available CPUs or cgroup limits change.

  • Disable Mechanism: These behaviors are automatically disabled if GOMAXPROCS is set explicitly or can be disabled with containermaxprocs=0 and updatemaxprocs=0 GODEBUG settings.

Experimental Garbage Collector​

  • A new garbage collector is available as an experiment. This design improves performance of marking and scanning small objects through better locality and CPU scalability. Benchmark results vary, but expect 10-40% reduction in garbage collection overhead.

  • Enable with GOEXPERIMENT=greenteagc at build time.

Trace Flight Recorder​

  • The new runtime/trace.FlightRecorder API provides a lightweight way to capture runtime execution traces by continuously recording into an in-memory ring buffer.

  • When a significant event occurs, call FlightRecorder.WriteTo to snapshot the last few seconds of the trace to a file.

Panic Output Change​

  • When a program exits due to an unhandled panic that was recovered and repanicked, the message no longer repeats the panic text.

Previously: panic: PANIC [recovered]\n panic: PANIC

Now: panic: PANIC [recovered, repanicked]

VMA Names on Linux​

  • On Linux systems with kernel support for anonymous VMA names, the Go runtime annotates anonymous memory mappings with context about their purpose (e.g., [anon: Go: heap]). Can be disabled with decoratemappings=0 GODEBUG setting.

Compiler​

nil Pointer Bug Fix​

  • Fixes a compiler bug from Go 1.21 that incorrectly delayed nil pointer checks. Programs that relied on this bug will now correctly panic.

DWARF 5 Support​

  • The compiler and linker now generate debug information using DWARF version 5. This reduces the space required for debugging information and linking time. Can be disabled with GOEXPERIMENT=nodwarf5.

Faster Slices​

  • The compiler can now allocate slice backing stores on the stack in more situations, improving performance. All new stack allocations can be turned off with -gcflags=all=-d=variablemakehash=n.

Linker​

  • The linker now accepts a -funcalign=N command line option to specify function entry alignment.

Standard Library​

New testing/synctest Package​

  • The new testing/synctest package provides support for testing concurrent code.

  • The Test function runs tests in an isolated "bubble" with virtualized time.

  • The Wait function waits for all goroutines in the current bubble to block.

This package was first available in Go 1.24 under GOEXPERIMENT=synctest. The experiment has now graduated to general availability.

New Experimental encoding/json/v2 Package​

  • Go 1.25 includes a new experimental JSON implementation, enabled by setting GOEXPERIMENT=jsonv2 at build time.

  • Two new packages are available:

  • The new implementation performs substantially better than the existing one under many scenarios. Decoding is substantially faster.

Other Standard Library Improvements​

  • archive/tar: Writer.AddFS now supports symbolic links for filesystems implementing io/fs.ReadLinkFS.

  • crypto: New MessageSigner interface and SignMessage function for signers that hash messages themselves.

  • crypto/ecdsa: New low-level encoding functions: ParseRawPrivateKey, ParseUncompressedPublicKey, PrivateKey.Bytes, and PublicKey.Bytes. FIPS 140-3 signing is now 4x faster.

  • crypto/ed25519: FIPS 140-3 signing is now 4x faster.

  • crypto/rsa: Key generation is now 3x faster.

  • crypto/sha1: Hashing is now 2x faster on amd64 with SHA-NI instructions.

  • crypto/sha3: Hashing is now 2x faster on Apple M processors. New SHA3.Clone method.

  • crypto/tls: New ConnectionState.CurveID field and Config.GetEncryptedClientHelloKeys callback. SHA-1 signatures are now disallowed in TLS 1.2 (can be re-enabled with tlssha1=1).

  • crypto/x509: Support for crypto.MessageSigner interface. CreateCertificate now uses truncated SHA-256 for SubjectKeyId.

  • go/ast: New PreorderStack function for AST traversal with node stack.

  • go/token: New FileSet.AddExistingFiles method.

  • go/types: Var now has a Kind method. New LookupSelection function.

  • hash: New XOF interface for extendable output functions. All standard library Hash implementations now implement Cloner.

  • io/fs: New ReadLinkFS interface for reading symbolic links.

  • net: LookupMX now returns DNS names that look like IP addresses. Windows ListenMulticastUDP now supports IPv6. Windows now implements FileConn, FilePacketConn, and FileListener.

  • net/http: New CrossOriginProtection implements CSRF protections using Fetch metadata.

  • os: Windows NewFile now supports asynchronous I/O handles. DirFS and Root.FS implement io/fs.ReadLinkFS. Root has new methods for file operations.

  • reflect: New TypeAssert function for direct type assertions without allocations.

  • regexp/syntax: \p{name} and \P{name} now accept more names and case-insensitive lookups.

  • runtime: AddCleanup cleanup functions are now executed concurrently and in parallel. New SetDefaultGOMAXPROCS function. New checkfinalizers=1 GODEBUG setting for diagnostics.

  • sync: New WaitGroup.Go method simplifies goroutine creation and counting.

  • testing: New T.Attr, B.Attr, and F.Attr methods for emitting test attributes. New Output method. AllocsPerRun now panics if parallel tests are running.

  • unique: More eager, efficient, and parallel value reclamation.

Platform Support​

Darwin (macOS)​

  • Go 1.25 requires macOS 12 Monterey or later. Support for previous versions is discontinued.

Windows​

  • Go 1.25 is the last release containing the broken 32-bit windows/arm port. It will be removed in Go 1.26.

AMD64​

  • In GOAMD64=v3 mode or higher, the compiler now uses fused multiply-add instructions for faster and more accurate floating-point arithmetic.

Loong64​

  • The linux/loong64 port now supports the race detector, cgo traceback, and internal linking mode.

RISC-V​

  • The linux/riscv64 port now supports the plugin build mode.
  • The GORISCV64 environment variable accepts a new value rva23u64 for the RVA23U64 user-mode profile.

References​

For more details, see the official release notes: Go 1.25 Release Notes