Go 1.26 Release Notes - The Go Programming Language

DRAFT RELEASE NOTES — Introduction to Go 1.26

Go 1.26 is not yet released. These are work-in-progress release notes. Go 1.26 is expected to be released in February 2026.

Changes to the language

The built-in new function, which creates a new variable, now allows its operand to be an expression, specifying the initial value of the variable.

This feature is particularly useful when working with serialization packages such as encoding/json or protocol buffers that use a pointer to represent an optional value, as it enables an optional field to be populated in a simple expression, for example:

import "encoding/json"

type Person struct {
    Name string   `json:"name"`
    Age  *int     `json:"age"` // age if known; nil otherwise
}

func personJSON(name string, born time.Time) ([]byte, error) {
    return json.Marshal(Person{
        Name: name,
        Age:  new(yearsSince(born)),
    })
}

func yearsSince(t time.Time) int {
    return int(time.Since(t).Hours() / (365.25 * 24)) // approximately
}

Go command

cmd/doc, and go tool doc have been deleted. go doc can be used as a replacement for go tool doc: it takes the same flags and arguments and has the same behavior.

The go fix command, following the pattern of go vet in Go 1.10, now uses the Go analysis framework (golang.org/x/tools/go/analysis). This means the same analyzers that provide diagnostics in go vet can be used to suggest and apply fixes in go fix. The go fix command’s historical fixers, all of which were obsolete, have been removed and replaced by a suite of new analyzers that offer fixes to use newer features of the language and library.

Pprof

The pprof tool web UI, enabled with the -http flag, now defaults to the flame graph view. The previous graph view is available in the “View -> Graph” menu, or via /ui/graph.

Runtime

New garbage collector

The Green Tea garbage collector, previously available as an experiment in Go 1.25, is now enabled by default after incorporating feedback.

This garbage collector’s design improves the performance of marking and scanning small objects through better locality and CPU scalability. Benchmark results vary, but we expect somewhere between a 10—40% reduction in garbage collection overhead in real-world programs that heavily use the garbage collector. Further improvements, on the order of 10% in garbage collection overhead, are expected when running on newer amd64-based CPU platforms (Intel Ice Lake or AMD Zen 4 and newer), as the garbage collector now leverages vector instructions for scanning small objects when possible.

The new garbage collector may be disabled by setting GOEXPERIMENT=nogreenteagc at build time. This opt-out setting is expected to be removed in Go 1.27. If you disable the new garbage collector for any reason related to its performance or behavior, please file an issue.

Faster cgo calls

The baseline runtime overhead of cgo calls has been reduced by ~30%.

Faster memory allocation

The compiler will now generate calls to size-specialized memory allocation routines, reducing the cost of some small (<512 byte) memory allocations by up to 30%. Improvements vary depending on the workload, but the overall improvement is expected to be ~1% in real allocation-heavy programs. Please file an issue if you notice any regressions. You may set GOEXPERIMENT=nosizespecializedmalloc at build time to disable it.

Goroutine leak profiles

A new profile type that reports leaked goroutines is now available as an experiment. The new profile type, named goroutineleak in the runtime/pprof package, may be enabled by setting GOEXPERIMENT=goroutineleakprofile at build time. Enabling the experiment also makes the profile available as a net/http/pprof endpoint, /debug/pprof/goroutineleak.

The following example showcases a real-world goroutine leak that can be revealed by the new profile:

type result struct {
    res workResult
    err error
}

func processWorkItems(ws []workItem) ([]workResult, error) {
    // Process work items in parallel, aggregating results in ch.
    ch := make(chan result)
    for _, w := range ws {
        go func() {
            res, err := processWorkItem(w)
            ch <- result{res, err}
        }()
    }

    // Collect the results from ch, or return an error if one is found.
    var results []workResult
    for range len(ws) {
        r := <-ch
        if r.err != nil {
            // This early return may cause goroutine leaks.
            return nil, r.err
        }
        results = append(results, r.res)
    }
    return results, nil
}

Because ch is unbuffered, if processWorkItems returns early due to an error, all remaining processWorkItem goroutines will leak. However, ch also becomes unreachable to all other goroutines not involved in the leak soon after the leak itself occurs. In general, the runtime is now equipped to identify and report on any goroutines blocked on operations over concurrency primitives (for example, channels, sync.Mutex, sync.Cond, and so forth) that are not reachable from runnable goroutines.

Note, however, that the runtime may fail to identify leaks caused by blocking on operations over concurrency primitives reachable through global variables or the local variables of runnable goroutines.

Special thanks to Vlad Saioc at Uber for contributing this work. The underlying theory is presented in detail in a publication by Saioc et al..

The implementation is production-ready, and is only considered an experiment for the purposes of collecting feedback on the API, specifically the choice to make it a new profile. The feature is also designed to not incur any additional run-time overhead unless it is actively in-use.

We encourage users to try out the new feature in the Go playground, in tests, in continuous integration, and in production. We welcome additional feedback on the proposal issue.

We aim to enable goroutine leak profiles by default in Go 1.27.

Compiler

The compiler can now allocate the backing store for slices on the stack in more situations, which improves performance. If this change is causing trouble, the bisect tool can be used to find the allocation causing trouble using the -compile=variablemake flag. All such new stack allocations can also be turned off using -gcflags=all=-d=variablemakehash=n.

Linker

On 64-bit ARM-based Windows (the windows/arm64 port), the linker now supports internal linking mode of cgo programs, which can be requested with the -ldflags=-linkmode=internal flag.

There are several minor changes to executable files. These changes do not affect running Go programs. They may affect programs that analyze Go executables, and they may affect people who use external linking mode with custom linker scripts.

• The moduledata structure is now in its own section, named go.module.
• The moduledata cutab field, which is a slice, now has the correct length; previously the length was four times too large.
• The pcHeader found at the start of the .gopclntab section no longer records the start of the text section. That field is now always zero.
• That pcHeader change was made so that the .gopclntab section no longer contains any relocations. On platforms that support relro, the section has moved from the relro segment to the rodata segment.
• The funcdata symbols and the findfunctab have moved from the .rodata section to the .gopclntab section.
• The .gosymtab section has been removed. It was previously always present but empty.
• When using internal linking, ELF sections now appear in the section header list sorted by address. The previous order was somewhat unpredictable.

The references to section names here use the ELF names as seen on Linux and other systems. The Mach-O names as seen on Darwin start with a double underscore and do not contain any dots.

Bootstrap

As mentioned in the Go 1.24 release notes, Go 1.26 now requires Go 1.24.6 or later for bootstrap. We expect that Go 1.28 will require a minor release of Go 1.26 or later for bootstrap.

Standard library

New crypto/hpke package

The new crypto/hpke package implements Hybrid Public Key Encryption (HPKE) as specified in RFC 9180, including support for post-quantum hybrid KEMs.

New experimental simd/archsimd package

Go 1.26 introduces a new experimental simd/archsimd package, which can be enabled by setting the environment variable GOEXPERIMENT=simd at build time. This package provides access to architecture-specific SIMD operations. It is currently available on the AMD64 architecture, supporting 128-bit, 256-bit, and 512-bit vectors.

See the proposal issue for more details.

New experimental runtime/secret package

The new runtime/secret package is available as an experiment, which can be enabled by setting the environment variable GOEXPERIMENT=runtimesecret at build time. It provides a facility for securely erasing temporaries used in code that manipulates secret information, typically cryptographic in nature. It currently supports the AMD64 and ARM64 architectures on Linux.

The secret.Do function runs its function argument and then erases all temporary storage (registers, stack, new heap allocations) used by that function argument. Heap storage is not erased until that storage is deemed unreachable by the garbage collector, which might take some time after secret.Do completes.

This package is intended to make it easier to ensure forward secrecy.

Minor changes to the library

bytes

The new Buffer.Peek method returns the next n bytes from the buffer without advancing it.

crypto

The new Encapsulator and Decapsulator interfaces allow accepting abstract KEM encapsulation or decapsulation keys.

crypto/dsa

The random parameter to GenerateKey is now ignored. Instead, it now always uses a secure source of cryptographically random bytes. For deterministic testing, use the new testing/cryptotest.SetGlobalRandom function. The new GODEBUG setting cryptocustomrand=1 temporarily restores the old behavior.

crypto/ecdh

The random parameter to Curve.GenerateKey is now ignored. Instead, it now always uses a secure source of cryptographically random bytes. For deterministic testing, use the new testing/cryptotest.SetGlobalRandom function. The new GODEBUG setting cryptocustomrand=1 temporarily restores the old behavior.

The new KeyExchanger interface, implemented by PrivateKey, makes it possible to accept abstract ECDH private keys, e.g. those implemented in hardware.

crypto/ecdsa

The big.Int fields of PublicKey and PrivateKey are now deprecated.

The random parameter to GenerateKey, SignASN1, Sign, and PrivateKey.Sign is now ignored. Instead, they now always use a secure source of cryptographically random bytes. For deterministic testing, use the new testing/cryptotest.SetGlobalRandom function. The new GODEBUG setting cryptocustomrand=1 temporarily restores the old behavior.

crypto/ed25519

If the random parameter to GenerateKey is nil, GenerateKey now always uses a secure source of cryptographically random bytes, instead of crypto/rand.Reader (which could have been overridden). The new GODEBUG setting cryptocustomrand=1 temporarily restores the old behavior.

crypto/fips140

The new WithoutEnforcement and Enforced functions now allow running in GODEBUG=fips140=only mode while selectively disabling the strict FIPS 140-3 checks.

Version returns the resolved FIPS 140-3 Go Cryptographic Module version when building against a frozen module with GOFIPS140.

crypto/mlkem

The new DecapsulationKey768.Encapsulator and DecapsulationKey1024.Encapsulator methods implement the new crypto.Decapsulator interface.

crypto/mlkem/mlkemtest

The new crypto/mlkem/mlkemtest package exposes the Encapsulate768 and Encapsulate1024 functions which implement derandomized ML-KEM encapsulation, for use with known-answer tests.

crypto/rand

The random parameter to Prime is now ignored. Instead, it now always uses a secure source of cryptographically random bytes. For deterministic testing, use the new testing/cryptotest.SetGlobalRandom function. The new GODEBUG setting cryptocustomrand=1 temporarily restores the old behavior.

crypto/rsa

The new EncryptOAEPWithOptions function allows specifying different hash functions for OAEP padding and MGF1 mask generation.

The random parameter to GenerateKey, GenerateMultiPrimeKey, and EncryptPKCS1v15 is now ignored. Instead, they now always use a secure source of cryptographically random bytes. For deterministic testing, use the new testing/cryptotest.SetGlobalRandom function. The new GODEBUG setting cryptocustomrand=1 temporarily restores the old behavior.

If PrivateKey fields are modified after calling PrivateKey.Precompute, PrivateKey.Validate now fails.

PrivateKey.D is now checked for consistency with precomputed values, even if it is not used.

Unsafe PKCS #1 v1.5 encryption padding (implemented by EncryptPKCS1v15, DecryptPKCS1v15, and DecryptPKCS1v15SessionKey) is now deprecated.

crypto/subtle

The WithDataIndependentTiming function no longer locks the calling goroutine to the OS thread while executing the passed function. Additionally, any goroutines which are spawned during the executed of the passed function and their descendents now inherit the properties of WithDataIndependentTiming for their lifetime. This change also affects cgo in the following ways:

• Any C code called via cgo from within the function passed to WithDataIndependentTiming, or from a goroutine spawned by the function passed to WithDataIndependentTiming and its descendents, will also have data independent timing enabled for the duration of the call. If the C code disables data independent timing, it will be re-enabled on return to Go.
• If C code called via cgo, from the function passed to WithDataIndependentTiming or elsewhere, enables or disables data independent timing then calling into Go will preserve that state for the duration of the call.

crypto/tls

The hybrid SecP256r1MLKEM768 and SecP384r1MLKEM1024 post-quantum key exchanges are now enabled by default. They can be disabled by setting Config.CurvePreferences or with the tlssecpmlkem=0 GODEBUG setting.

The new ClientHelloInfo.HelloRetryRequest field indicates if the ClientHello was sent in response to a HelloRetryRequest message. The new ConnectionState.HelloRetryRequest field indicates if the server sent a HelloRetryRequest, or if the client received a HelloRetryRequest, depending on connection role.

The QUICConn type used by QUIC implementations includes a new event for reporting TLS handshake errors.

If Certificate.PrivateKey implements crypto.MessageSigner, its SignMessage method is used instead of Sign in TLS 1.2 and later.

The following GODEBUG settings introduced in Go 1.22 and Go 1.23 will be removed in the next major Go release. Starting in Go 1.27, the new behavior will apply regardless of GODEBUG setting or go.mod language version.

• tlsunsafeekm: ConnectionState.ExportKeyingMaterial will require TLS 1.3 or Extended Master Secret.
• tlsrsakex: legacy RSA-only key exchanges without ECDH won’t be enabled by default.
• tls10server: the default minimum TLS version for both clients and servers will be TLS 1.2.
• tls3des: the default cipher suites will not include 3DES.
• x509keypairleaf: X509KeyPair and LoadX509KeyPair will always populate the Certificate.Leaf field.

crypto/x509

The ExtKeyUsage and KeyUsage types now have String methods that return the corresponding OID names as defined in RFC 5280 and other registries.

The ExtKeyUsage type now has an OID method that returns the corresponding OID for the EKU.

The new OIDFromASN1OID function allows converting an encoding/asn1.ObjectIdentifier into an OID.

debug/elf

Additional R_LARCH_* constants from LoongArch ELF psABI v20250521 (global version v2.40) are defined for use with LoongArch systems.

errors

The new AsType function is a generic version of As. It is type-safe, faster, and, in most cases, easier to use.

fmt

For unformatted strings, fmt.Errorf("x") now allocates less and generally matches the allocations for errors.New("x").

go/ast

The new ParseDirective function parses directive comments, which are comments such as //go:generate. Source code tools can support their own directive comments and this new API should help them implement the conventional syntax.

The new BasicLit.ValueEnd field records the precise end position of a literal so that the BasicLit.End method can now always return the correct answer. (Previously it was computed using a heuristic that was incorrect for multi-line raw string literals in Windows source files, due to removal of carriage returns.)

Programs that update the ValuePos field of BasicLits produced by the parser may need to also update or clear the ValueEnd field to avoid minor differences in formatted output.

go/token

The new File.End convenience method returns the file’s end position.

go/types

The gotypesalias GODEBUG setting introduced in Go 1.22 will be removed in the next major Go release. Starting in Go 1.27, the go/types package will always produce an Alias type for the representation of type aliases regardless of GODEBUG setting or go.mod language version.

image/jpeg

The JPEG encoder and decoder have been replaced with new, faster, more accurate implementations. Code that expects specific bit-for-bit outputs from the encoder or decoder may need to be updated.

io

ReadAll now allocates less intermediate memory and returns a minimally sized final slice. It is often about two times faster while typically allocating around half as much total memory, with more benefit for larger inputs.

log/slog

The NewMultiHandler function creates a MultiHandler that invokes all the given Handlers. Its Enable method reports whether any of the handlers’ Enabled methods return true. Its Handle, WithAttr and WithGroup methods call the corresponding method on each of the enabled handlers.

net

The new Dialer methods DialIP, DialTCP, DialUDP, and DialUnix permit dialing specific network types with context values.

net/http

The new HTTP2Config.StrictMaxConcurrentRequests field controls whether a new connection should be opened if an existing HTTP/2 connection has exceeded its stream limit.

The new Transport.NewClientConn method returns a client connection to an HTTP server. Most users should continue to use Transport.RoundTrip to make requests, which manages a pool of connections. NewClientConn is useful for users who need to implement their own connection management.

Client now uses and sets cookies scoped to URLs with the host portion matching Request.Host when available. Previously, the connection address host was always used.

net/http/httptest

The HTTP client returned by Server.Client will now redirect requests for example.com and any subdomains to the server being tested.

net/http/httputil

The ReverseProxy.Director configuration field is deprecated in favor of ReverseProxy.Rewrite.

A malicious client can remove headers added by a Director function by designating those headers as hop-by-hop. Since there is no way to address this problem within the scope of the Director API, we added a new Rewrite hook in Go 1.20. Rewrite hooks are provided with both the unmodified inbound request received by the proxy and the outbound request which will be sent by the proxy.

Since the Director hook is fundamentally unsafe, we are now deprecating it.

net/netip

The new Prefix.Compare method compares two prefixes.

net/url

Parse now rejects malformed URLs containing colons in the host subcomponent, such as http://::1/ or http://localhost:80:80/. URLs containing bracketed IPv6 addresses, such as http://[::1]/ are still accepted. The new GODEBUG setting urlstrictcolons=0 restores the old behavior.

os

The new Process.WithHandle method provides access to an internal process handle on supported platforms (Linux 5.4 or later, and Windows). On Linux, the process handle is a pidfd. The method returns ErrNoHandle on unsupported platforms or when no process handle is available.

On Windows, the OpenFile flag parameter can now contain any combination of Windows-specific file flags, such as FILE_FLAG_OVERLAPPED and FILE_FLAG_SEQUENTIAL_SCAN, for control of file or device caching behavior, access modes, and other special-purpose flags.

os/signal

NotifyContext now cancels the returned context with context.CancelCauseFunc and an error indicating which signal was received.

reflect

The new methods Type.Fields, Type.Methods, Type.Ins and Type.Outs return iterators for a type’s fields (for a struct type), methods, inputs and outputs parameters (for a function type), respectively.

Similarly, the new methods Value.Fields and Value.Methods return iterators over a value’s fields or methods, respectively. Each iteration yields the type information (StructField or Method) of a field or method, along with the field or method Value.

runtime/metrics

Several new scheduler metrics have been added, including counts of goroutines in various states (waiting, runnable, etc.) under the /sched/goroutines prefix, the number of OS threads the runtime is aware of with /sched/threads:threads, and the total number of goroutines created by the program with /sched/goroutines-created:goroutines.

testing

The new methods T.ArtifactDir, B.ArtifactDir, and F.ArtifactDir return a directory in which to write test output files (artifacts).

When the -artifacts flag is provided to go test, this directory will be located under the output directory (specified with -outputdir, or the current directory by default). Otherwise, artifacts are stored in a temporary directory which is removed after the test completes.

The first call to ArtifactDir when -artifacts is provided writes the location of the directory to the test log.

For example, in a test named TestArtifacts, t.ArtifactDir() emits:

=== ARTIFACTS Test /path/to/artifact/dir

testing/cryptotest

The new SetGlobalRandom function configures a global, deterministic cryptographic randomness source for the duration of the test. It affects crypto/rand, and all implicit sources of cryptographic randomness in the crypto/... packages.

time

The asynctimerchan GODEBUG setting introduced in Go 1.23 will be removed in the next major Go release. Starting in Go 1.27, the time package will always use unbuffered (synchronous) channels for timers regardless of GODEBUG setting or go.mod language version.

Ports

Darwin

Go 1.26 is the last release that will run on macOS 12 Monterey. Go 1.27 will require macOS 13 Ventura or later.

FreeBSD

The freebsd/riscv64 port (GOOS=freebsd GOARCH=riscv64) has been marked broken. See issue 76475 for details.

Windows

As announced in the Go 1.25 release notes, the broken 32-bit windows/arm port (GOOS=windows GOARCH=arm) is removed.

PowerPC

Go 1.26 is the last release that supports the big-endian 64-bit PowerPC port on Linux (GOOS=linux GOARCH=ppc64). The port will be removed in Go 1.27.

S390X

The s390x port now supports passing function arguments and results using registers.

RISC-V

The linux/riscv64 port now supports the race detector.