# Go 1 27 > Apply Go 1.27 language features, tooling, standard-library APIs, migrations, and behaviour changes. Load for Go work targeting 1.27 or later when the model's knowledge may predate the 2026-08-19 release. - Skill: `cedws/go-1-27` (Agent Skill) - Install (CLI): `npx skillmds@latest add cedws/go-1-27` - Raw SKILL.md: https://api.skillmd.com/api/skills/cedws/go-1-27/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: cedws (https://skillmd.com/u/cedws) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/cedws/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.