Go 1 27

Go 1.27

This overview applies when the project's target Go version is at least 1.27.

Language

• Methods may declare their own type parameters. Interface methods cannot declare type parameters, and generic methods cannot implement interface methods.
• Keys in struct literals may be field selectors, including selectors that name fields within embedded structs.
• Generic function type inference applies whenever a function is assigned or converted to a matching function type.

Tools and modules

• The compile, link, asm, cgo, cover, and pack tools accept GCC-style response files through @file arguments.
• The go command no longer fetches modules from Bazaar (bzr) servers.
• Removed GODEBUG settings remain accepted in go.mod and //go:debug only when set to their final default. Earlier values cause the build to fail.
• go test runs the stdversion vet check by default. It identifies standard library symbols newer than the version selected by the module and file tags.
• go test -json output events may include OutputType values such as error, error-continue, and frame.
• go doc accepts package@version; -ex lists executable examples and a named example includes its source and comments.
• go fix adds the atomictypes, embedlit, slicesbackward, and unsafefuncs modernisers. The fmtappendf analyser is removed, and waitgroup is renamed to waitgroupgo.
• go mod tidy for modules at Go 1.27 or later consolidates requirements into at most one direct and one indirect block while preserving associated comments.
• A port-only go tool trace -http=:6060 address binds to localhost. An explicit address such as 0.0.0.0:6060 exposes it on all interfaces.

Runtime and diagnostics

• Tracebacks include runtime/pprof goroutine labels for Go 1.27 modules. GODEBUG=tracebacklabels=0 disables them when labels contain sensitive data.
• Time package channels are always synchronous. The asynctimerchan compatibility setting is permanently removed.
• The goroutineleak profile and /debug/pprof/goroutineleak endpoint are generally available. Detection is reachability-based and cannot identify every permanently blocked goroutine; GOEXPERIMENT=goroutineleakprofile is removed.
• Size-specialised allocation is enabled for small allocations and adds roughly 60 KB to binaries. GOEXPERIMENT=nosizespecializedmalloc is a temporary opt-out expected to disappear in Go 1.28.

Standard library

• encoding/json/v2 supplies option-based marshal and unmarshal APIs, including reader, writer, encoder, and decoder forms. Its defaults reject invalid UTF-8 and duplicate object names.
• encoding/json/jsontext provides token- and value-level JSON processing with stateful validation. Numeric token accessors return errors.
• encoding/json is backed by the v2 implementation while retaining v1 behaviour and support; error text may differ. Compatibility options expose v1 semantics, and GOEXPERIMENT=nojsonv2 temporarily restores the old implementation.
• crypto/mldsa implements FIPS 204 ML-DSA. crypto/x509 supports ML-DSA keys and signatures, and TLS 1.3 supports the ML-DSA signature schemes.
• uuid generates and parses UUIDs.
• bytes.CutLast and strings.CutLast split around the last separator occurrence, covering common LastIndex patterns.
• compress/flate may produce different valid bytes, affecting ZIP, gzip, zlib, and PNG output derived from it.
• crypto/tls.Config.Rand is deprecated; testing/cryptotest.SetGlobalRandom provides deterministic randomness for tests. MLKEM1024 is available through CurvePreferences, and ConnectionState.LocalCertificate reports the chain presented to the peer.
• crypto/x509.SystemCertPool honours SSL_CERT_FILE and SSL_CERT_DIR on Windows and Darwin, selecting the Go verifier when either is set.
• database/sql.ConvertAssign exposes Rows.Scan conversions to drivers, while driver.RowsColumnScanner permits direct scanning into caller destinations.
• go/types.Hasher and HasherIgnoreTags hash types according to the corresponding identity relations. The removed gotypesalias setting means alias declarations always produce Alias nodes.
• hash/maphash.Hasher defines hashing and equality for a type; ComparableHasher implements that contract for comparable values.
• math/big.Int.Divide computes quotient and remainder with truncation, floor, round, or ceiling modes. math/rand/v2.Rand.N is the method form of N.
• Unix connection reads return io.EOF directly rather than a wrapping net.OpError when the underlying read reaches EOF.
• HTTP/2 servers honour RFC 9218 client priority signals unless Server.DisableClientPriority is set. Closing an HTTP/1 response body drains a bounded amount of unread content to improve connection reuse.
• http.Server.MaxHeaderValueCount limits accepted header values. httptest.NewTestServer uses an in-memory network compatible with testing/synctest.
• url.URL.Clone and url.Values.Clone make deep copies. testing/synctest.Sleep combines time.Sleep with synctest.Wait.
• Unicode support advances from Unicode 15 to Unicode 17.

Experimental features

• GOEXPERIMENT=simd enables the experimental portable, vector-size-agnostic simd package. Its operations use hardware instructions where available.
• The same experiment enables the unstable, non-portable simd/archsimd package. It supports amd64, arm64 Neon, and WebAssembly vector operations with APIs tied to each architecture.

Compatibility and platforms

• Relative filenames in //line and /*line*/ directives resolve from the containing source file's directory.
• Closure symbol names are simpler and may be shared across inlined instances. Tests that inspect those symbols can observe different names, and function code pointers remain unsuitable for comparing closures.
• The tlsunsafeekm, tlsrsakex, tls3des, tls10server, and x509keypairleaf GODEBUG compatibility settings are permanently removed.
• macOS builds require macOS 13 Ventura or later.
• Linux ppc64 uses the ELFv2 ABI. Cgo, position-independent executables, and external linking require an ELFv2-compatible runtime and Linux kernel support.