Go 1 26

Go 1.26

This overview applies when the project's target Go version is at least 1.26.

Language

• new(expression) is available when an API needs a pointer to an initial value, especially for optional serialization fields. Prefer it to a temporary variable whose only purpose is taking an address.
• Available capability: self-referential generic constraints when an operation must accept and return the concrete implementing type.

type Adder[A Adder[A]] interface {
	Add(A) A
}

Tools and modules

• go fix can apply behaviour-preserving modernisers for current language and standard-library idioms. Use //go:fix inline directives when maintaining an API whose callers need a source-level migration.
• After go mod init, set the intended compatibility explicitly when it differs from the generated default. A Go 1.26 toolchain initially writes go 1.25.0.
• Replacement: go tool doc with go doc; the former has been removed.
• pprof -http opens in flame-graph view; the graph view remains selectable explicitly.

Runtime and diagnostics

• Available capability: the Green Tea garbage collector as the default. Enable GOEXPERIMENT=nogreenteagc only as a temporary diagnostic opt-out and report behaviour or performance regressions.
• GOEXPERIMENT=goroutineleakprofile enables investigate unreachable, permanently blocked goroutines. Inspect the goroutineleak profile through runtime/pprof or /debug/pprof/goroutineleak, and account for its reachability-based detection limits.
• 64-bit heap base randomisation is enabled. GOEXPERIMENT=norandomizedheapbase64 provides a diagnostic opt-out.

Standard library

• crypto/hpke supports RFC 9180 Hybrid Public Key Encryption, including supported post-quantum hybrid KEMs.
• errors.AsType[T] is the modern alternative to errors.As in most typed error extraction because it is type-safe and avoids an output pointer.
• bytes.Buffer.Peek can inspect buffered bytes without advancing the buffer.
• log/slog.NewMultiHandler is available when one record must be dispatched to several handlers while preserving each handler's Enabled decision.
• Available capability: the context-aware net.Dialer.DialIP, DialTCP, DialUDP, and DialUnix methods when a concrete network type is required.
• Established API: http.Transport.RoundTrip for managed connection pooling. Use Transport.NewClientConn only when implementing custom connection management.
• Replacement: httputil.ReverseProxy.Director with ReverseProxy.Rewrite; Director is deprecated because clients can remove headers it adds through hop-by-hop header declarations.
• Available capability: the new reflect field, method, input, and output iterators instead of index loops when iterating reflection metadata or values.

Cryptography

• Unsupported or discouraged: inject randomness through the reader parameters of affected crypto/dsa, crypto/ecdh, crypto/ecdsa, crypto/rand, or crypto/rsa operations; Go 1.26 ignores them and uses a secure global source.
• testing/cryptotest.SetGlobalRandom supports deterministic cryptographic tests. Treat GODEBUG=cryptocustomrand=1 as temporary migration support.
• Migration note: away from the deprecated big.Int fields of ECDSA keys and from deprecated RSA PKCS #1 v1.5 encryption. Prefer modern key APIs and OAEP-based encryption.
• The hybrid SecP256r1MLKEM768 and SecP384r1MLKEM1024 TLS key exchanges are enabled by default. Config.CurvePreferences expresses an explicit protocol policy.

Testing

• Test artefact support: persistent test output through T.ArtifactDir, B.ArtifactDir, or F.ArtifactDir, and run go test -artifacts when the artefacts must survive the test process.
• for b.Loop() { ... } is the modern alternative to for i := 0; i < b.N; i++ { ... }; Go 1.26 permits inlining in the loop body while retaining benchmark work against elimination.

Experimental features

• Experimental or compatibility option: GOEXPERIMENT=simd only for architecture-specific amd64 SIMD evaluation. Treat simd/archsimd as unstable and non-portable.
• Experimental or compatibility option: GOEXPERIMENT=runtimesecret only on Linux amd64 or arm64 when evaluating secure erasure of cryptographic temporaries. Treat the API as unstable.

Compatibility

• Unsupported or discouraged: compare JPEG encoder output bit-for-bit across the upgrade; the encoder and decoder implementations changed.
• ServeMux trailing-slash redirects now use status 307, and that net/url.Parse rejects malformed host colons. Use GODEBUG=urlstrictcolons=0 only while migrating malformed inputs.
• Compatibility outlook: for Go 1.27 to remove compatibility switches for older TLS defaults, go/types alias representation, and asynchronous timer channels.
• Platform requirement: macOS 12 or later, plan to require macOS 13 with Go 1.27, and remove any windows/arm build target.