Go 1.26 Release Features

Quick reference for Go 1.26 new features, API changes, and migration notes.

Language Changes

new() Accepts Expressions

// Before: needed helper function or temp variable
v := 42
ptr := &v

// Go 1.26: direct expression in new()
ptr := new(42)
Age: new(yearsSince(born))  // useful for optional pointer fields

Self-Referential Generic Types

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

func algo[A Adder[A]](x, y A) A {
    return x.Add(y)
}

Runtime

Green Tea GC (Default)

• 10-40% reduction in GC overhead for real-world programs
• +10% on newer amd64 CPUs (Ice Lake+, Zen 4+) via vector instructions
• Disable: GOEXPERIMENT=nogreenteagc (removal expected Go 1.27)

Heap Base Address Randomization

• 64-bit platforms randomize heap base at startup (security)
• Disable: GOEXPERIMENT=norandomizedheapbase64

Faster cgo (~30% overhead reduction)

Goroutine Leak Profile (Experimental)

• Enable: GOEXPERIMENT=goroutineleakprofile
• New goroutineleak profile type in runtime/pprof
• HTTP endpoint: /debug/pprof/goroutineleak
• GC-based detection of goroutines blocked on unreachable primitives

Tools

go fix Revamped

• Complete overhaul with modernizers framework
• Source-level inliner with //go:fix inline directives
• Built on Go analysis framework

go mod init Defaults

• Now defaults to go 1.(N-1).0 (e.g., Go 1.26 creates go 1.25.0)
• Override with go get go@version

Pprof

• Web UI -http flag now defaults to flame graph view

Compiler & Linker

• Stack allocation: Slice backing store on stack in more situations
• windows/arm64: Internal linking mode for cgo (-ldflags=-linkmode=internal)
• cmd/doc removed (use go doc)

New Standard Library Packages

crypto/hpke

Hybrid Public Key Encryption (RFC 9180) with post-quantum hybrid KEM support.

simd/archsimd (Experimental)

// Enable: GOEXPERIMENT=simd
// amd64 only: 128/256/512-bit vector types
var a, b archsimd.Int8x16
result := a.Add(b)

runtime/secret (Experimental)

Secure erasure of cryptographic temporaries. Enable: GOEXPERIMENT=runtimesecret. amd64/arm64 Linux only.

Key Standard Library Changes

errors

// New generic, type-safe, faster version of As
var target *MyError
if err, ok := errors.AsType[*MyError](err); ok {
    // use err directly - no need for As + target variable
}

io

• ReadAll() ~2x faster, ~50% less memory allocation, returns minimal-sized slice

reflect (Iterators)

for i, f := range reflect.TypeFor[MyStruct]().Fields() {
    fmt.Println(f.Name)
}
for i, m := range reflect.TypeFor[MyInterface]().Methods() {
    fmt.Println(m.Name)
}
// Also: Type.Ins(), Type.Outs(), Value.Fields(), Value.Methods()

log/slog

// New multi-handler
h := slog.NewMultiHandler(jsonHandler, textHandler)
logger := slog.New(h)

bytes

// New Peek method - read without advancing
data := buf.Peek(10)

net

// New typed Dial methods with context
d := &net.Dialer{}
conn, err := d.DialTCP(ctx, "tcp", addr)
conn, err := d.DialUDP(ctx, "udp", addr)
conn, err := d.DialIP(ctx, "ip4:icmp", addr)
conn, err := d.DialUnix(ctx, "unix", addr)

net/http

• ServeMux trailing slash redirects: now 307 (was 301)
• New HTTP2Config.StrictMaxConcurrentRequests
• New Transport.NewClientConn()
• httptest.Server.Client() redirects example.com to test server

net/url

• Parse() rejects malformed http://::1/ (use http://[::1]/)
• Restore: GODEBUG=urlstrictcolons=0

os

• New Process.WithHandle() (pidfd on Linux 5.4+, Handle on Windows)
• OpenFile accepts Windows-specific flags

testing

// New ArtifactDir for test output files
dir := t.ArtifactDir()
os.WriteFile(filepath.Join(dir, "debug.log"), data, 0644)

runtime/metrics

• /sched/goroutines (by state), /sched/threads:threads, /sched/goroutines-created:goroutines

fmt

• Errorf("x") allocates less (matches errors.New("x"))

image/jpeg

• Encoder/decoder replaced with faster, more accurate implementations
• Breaking: bit-for-bit output may differ

Crypto Changes

Post-Quantum TLS (Default)

• SecP256r1MLKEM768 and SecP384r1MLKEM1024 enabled by default
• Disable: GODEBUG=tlssecpmlkem=0 or Config.CurvePreferences

Random Parameter Changes

Many crypto functions now ignore the random parameter and always use secure randomness:

• crypto/dsa.GenerateKey
• crypto/ecdh.Curve.GenerateKey
• crypto/ecdsa.GenerateKey, SignASN1, Sign
• crypto/rand.Prime
• crypto/rsa.GenerateKey, EncryptPKCS1v15

Testing: use testing/cryptotest.SetGlobalRandom. Restore: GODEBUG=cryptocustomrand=1.

Deprecations

• crypto/rsa: PKCS #1 v1.5 functions (EncryptPKCS1v15, DecryptPKCS1v15)
• crypto/ecdsa: PublicKey/PrivateKey big.Int fields
• net/http/httputil: ReverseProxy.Director (use Rewrite)

GODEBUG Removals in Go 1.27

These GODEBUG settings are deprecated and will be removed:

• tlsunsafeekm, tlsrsakex, tls10server, tls3des
• x509keypairleaf, gotypesalias, asynctimerchan

Port Changes

• macOS: Last release for macOS 12 Monterey (Go 1.27 requires 13+)
• windows/arm (32-bit): Removed
• linux/riscv64: Race detector now supported
• WebAssembly: Significantly reduced memory for heaps <16 MiB
• linux/ppc64: Last release for ELFv1 ABI

Bootstrap

• Requires Go 1.24.6+ to build
• Go 1.28 will require Go 1.26+