_content/doc/go1.24.md

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title: Go 1.24 Release Notes
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## DRAFT RELEASE NOTES — Introduction to Go 1.24 {#introduction}

**Go 1.24 is not yet released. These are work-in-progress release notes.
Go 1.24 is expected to be released in February 2025.**

## Changes to the language {#language}

<!-- go.dev/issue/46477 -->
Go 1.24 now fully supports [generic type aliases](/issue/46477): a type alias
may be parameterized like a defined type.
See the [language spec](/ref/spec#Alias_declarations) for details.
For now, the feature can be disabled by setting `GOEXPERIMENT=noaliastypeparams`;
but the `aliastypeparams` setting will be removed for Go 1.25.

## Tools {#tools}

### Go command {#go-command}

<!-- go.dev/issue/48429 -->

Go modules can now track executable dependencies using `tool` directives in
go.mod. This removes the need for the previous workaround of adding tools as
blank imports to a file conventionally named "tools.go". The `go tool`
command can now run these tools in addition to tools shipped with the Go
distribution. For more information see [the
documentation](/doc/modules/managing-dependencies#tools).

The new `-tool` flag for `go get` causes a tool directive to be added to the
current module for named packages in addition to adding require directives.

The new [`tool` meta-pattern](/cmd/go#hdr-Package_lists_and_patterns) refers to
all tools in the current module. This can be used to upgrade them all with `go get -u tool` or to install them into your GOBIN directory with `go install tool`.

<!-- go.dev/issue/69290 -->

Executables created by `go run` and the new behavior for `go tool` are now
cached in the Go build cache. This makes repeated executions faster at the
expense of making the cache larger. See [#69290](/issue/69290).

<!-- go.dev/issue/62067 -->

The `go build` and `go install` commands now accept a `-json` flag that reports
build output and failures as structured JSON output on standard output.
For details of the reporting format, see `go help buildjson`.

Furthermore, `go test -json` now reports build output and failures in JSON,
interleaved with test result JSON.
These are distinguished by new `Action` types, but if they cause problems in
a test integration system, you can revert to the text build output by setting
`GODEBUG=gotestjsonbuildtext=1`.

### Cgo {#cgo}

<!-- go.dev/issue/56378, CL 579955 -->
Cgo supports new annotations for C functions to improve run time
performance.
`#cgo noescape cFunctionName` tells the compiler that memory passed to
the C function `cFunctionname` does not escape.
`#cgo nocallback cFunctionName` tells the compiler that the C function
`cFunctionName` does not call back to any Go functions.
For more information, see [the cgo documentation](/pkg/cmd/cgo#hdr-Optimizing_calls_of_C_code).

<!-- go.dev/issue/67699 -->
Cgo currently refuses to compile calls to a C function which has multiple
incompatible declarations. For instance, if `f` is declared as both `void f(int)`
and `void f(double)`, cgo will report an error instead of possibly generating an
incorrect call sequence for `f(0)`. New in this release is a better detector for
this error condition when the incompatible declarations appear in different
files. See [#67699](/issue/67699).

### Vet

<!-- go.dev/issue/44251 -->
The new `tests` analyzer reports common mistakes in declarations of
tests, fuzzers, benchmarks, and examples in test packages, such as
malformed names, incorrect signatures, or examples that document
non-existent identifiers. Some of these mistakes may cause tests not
to run.
This analyzer is among the subset of analyzers that are run by `go test`.

<!-- go.dev/issue/60529 -->
The existing `printf` analyzer now reports a diagnostic for calls of
the form `fmt.Printf(s)`, where `s` is a non-constant format string,
with no other arguments. Such calls are nearly always a mistake
as the value of `s` may contain the `%` symbol; use `fmt.Print` instead.
See [#60529](/issue/60529).

<!-- go.dev/issue/64127 -->
The existing `buildtag` analyzer now reports a diagnostic when
there is an invalid Go [major version build constraint](/pkg/cmd/go#hdr-Build_constraints)
within a `//go:build` directive. For example, `//go:build go1.23.1` refers to
a point release; use `//go:build go1.23` instead.
See [#64127](/issue/64127).

<!-- go.dev/issue/66387 -->
The existing `copylock` analyzer now reports a diagnostic when a
variable declared in a 3-clause "for" loop such as
`for i := iter(); done(i); i = next(i) { ... }` contains a `sync.Locker`,
such as a `sync.Mutex`. [Go 1.22](/doc/go1.22#language) changed the behavior
of these loops to create a new variable for each iteration, copying the
value from the previous iteration; this copy operation is not safe for locks.
See [#66387](/issue/66387).

### GOCACHEPROG

<!-- go.dev/issue/64876 -->
The `cmd/go` internal binary and test caching mechanism can now be implemented
by child processes implementing a JSON protocol between the `cmd/go` tool
and the child process named by the `GOCACHEPROG` environment variable.
This was previously behind a GOEXPERIMENT.
For protocol details, see [#59719](/issue/59719).

## Runtime {#runtime}

<!-- go.dev/issue/54766 -->
<!-- go.dev/cl/614795 -->
<!-- go.dev/issue/68578 -->

Several performance improvements to the runtime have decreased CPU overheads by
2—3% on average across a suite of representative benchmarks.
Results may vary by application.
These improvements include a new builtin `map` implementation based on
[Swiss Tables](https://abseil.io/about/design/swisstables), more efficient
memory allocation of small objects, and a new runtime-internal mutex
implementation.

The new builtin `map` implementation and new runtime-internal mutex may be
disabled by setting `GOEXPERIMENT=noswissmap` and `GOEXPERIMENT=nospinbitmutex`
at build time respectively.

## Compiler {#compiler}

<!-- go.dev/issue/60725, go.dev/issue/57926 -->
The compiler already disallowed defining new methods with receiver types that were
cgo-generated, but it was possible to circumvent that restriction via an alias type.
Go 1.24 now always reports an error if a receiver denotes a cgo-generated type,
whether directly or indirectly (through an alias type).

## Linker {#linker}

<!-- go.dev/issue/68678, go.dev/issue/68652, CL 618598, CL 618601 -->
The linker now generates a GNU build ID (the ELF `NT_GNU_BUILD_ID` note) on ELF platforms
and a UUID (the Mach-O `LC_UUID` load command) on macOS by default.
The build ID or UUID is derived from the Go build ID.
It can be disabled by the `-B none` linker flag, or overridden by the `-B 0xNNNN` linker
flag with a user-specified hexadecimal value.

## Bootstrap {#bootstrap}

<!-- go.dev/issue/64751 -->
As mentioned in the [Go 1.22 release notes](/doc/go1.22#bootstrap), Go 1.24 now requires
Go 1.22.6 or later for bootstrap.
We expect that Go 1.26 will require a point release of Go 1.24 or later for bootstrap.

## Standard library {#library}

### Directory-limited filesystem access

<!-- go.dev/issue/67002 -->
The new [`os.Root`](/pkg/os#Root) type provides the ability to perform filesystem
operations within a specific directory.

The [`os.OpenRoot`](/pkg/os#OpenRoot) function opens a directory and returns an [`os.Root`](/pkg/os#Root).
Methods on [`os.Root`](/pkg/os#Root) operate within the directory and do not permit
paths that refer to locations outside the directory, including
ones that follow symbolic links out of the directory.

- [`os.Root.Open`](/pkg/os#Root.Open) opens a file for reading.
- [`os.Root.Create`](/pkg/os#Root.Create) creates a file.
- [`os.Root.OpenFile`](/pkg/os#Root.OpenFile) is the generalized open call.
- [`os.Root.Mkdir`](/pkg/os#Root.Mkdir) creates a directory.

### New benchmark function

Benchmarks may now use the faster and less error-prone [`testing.B.Loop`](/pkg/testing#B.Loop) method to perform benchmark iterations like `for b.Loop() { ... }` in place of the typical loop structures involving `b.N` like `for range b.N`. This offers two significant advantages:
 - The benchmark function will execute exactly once per -count, so expensive setup and cleanup steps execute only once.
 - Function call parameters and results are kept alive, preventing the compiler from fully optimizing away the loop body.

### New crypto/hkdf package {#crypto-hkdf}

<!-- go.dev/issue/61477 -->
The new [`crypto/hkdf`](/pkg/crypto/hkdf/) package implements the HMAC-based Extract-and-Expand
Key Derivation Function (HKDF) as defined in RFC 5869. It is based on the pre-existing
`golang.org/x/crypto/hkdf` package.

### New crypto/mlkem package {#crypto-mlkem}

<!-- go.dev/issue/70122 -->
The new [`crypto/mlkem`](/pkg/crypto/mlkem/) package implements ML-KEM (formerly known as
Kyber), as specified in [NIST FIPS 203](https://doi.org/10.6028/NIST.FIPS.203).

### New crypto/pbkdf2 package {#crypto-pbkdf2}

<!-- go.dev/issue/69488 -->
The new [`crypto/pbkdf2`](/pkg/crypto/pbkdf2/) package implements the key derivation function
PBKDF2 as defined in RFC 2898 / PKCS #5 v2.0. It is based on the pre-existing
`golang.org/x/crypto/pbkdf2` package.

### New crypto/sha3 package {#crypto-sha3}

<!-- go.dev/issue/69982, go.dev/issue/65269, CL 629176 -->
The new [`crypto/sha3`](/pkg/crypto/sha3/) package implements the SHA-3 hash function, and SHAKE and
cSHAKE extendable-output functions. It is based on the pre-existing
`golang.org/x/crypto/sha3` package.

### New weak package {#weak}

The new [`weak`](/pkg/weak/) package provides weak pointers.

Weak pointers are a low-level primitive provided to enable the
creation of memory-efficient structures, such as weak maps for
associating values, canonicalization maps for anything not
covered by package [`unique`](/pkg/unique/), and various kinds
of caches.
For supporting these use-cases, this release also provides
[`runtime.AddCleanup`](/pkg/runtime/#AddCleanup) and
[`maphash.Comparable`](/pkg/maphash/#Comparable).

### Minor changes to the library {#minor_library_changes}

#### [`archive`](/pkg/archive/)

The `(*Writer).AddFS` implementations in both `archive/zip` and `archive/tar`
now write a directory header for an empty directory.

#### [`bytes`](/pkg/bytes/)

The [`bytes`](/pkg/bytes) package adds several functions that work with iterators:
- [`Lines`](/pkg/bytes#Lines) returns an iterator over the
  newline-terminated lines in the byte slice s.
- [`SplitSeq`](/pkg/bytes#SplitSeq) returns an iterator over
  all substrings of s separated by sep.
- [`SplitAfterSeq`](/pkg/bytes#SplitAfterSeq) returns an iterator
  over substrings of s split after each instance of sep.
- [`FieldsSeq`](/pkg/bytes#FieldsSeq) returns an iterator over
  substrings of s split around runs of whitespace characters,
  as defined by unicode.IsSpace.
- [`FieldsFuncSeq`](/pkg/bytes#FieldsFuncSeq) returns an iterator
  over substrings of s split around runs of Unicode code points satisfying f(c).

#### [`crypto/cipher`](/pkg/crypto/cipher/)

[`NewOFB`](/pkg/crypto/cipher#NewOFB), [`NewCFBEncrypter`](/pkg/crypto/cipher#NewCFBEncrypter), and [`NewCFBDecrypter`](/pkg/crypto/cipher#NewCFBDecrypter) are now deprecated. OFB and
CFB mode are not authenticated, which generally enables active attacks to
manipulate and recover the plaintext. It is recommended that applications use
[`AEAD`](/pkg/crypto/cipher#AEAD) modes instead. If an unauthenticated [`Stream`](/pkg/crypto/cipher#Stream) mode is required, use
[`NewCTR`](/pkg/crypto/cipher#NewCTR) instead.

The new [`NewGCMWithRandomNonce`](/pkg/crypto/cipher#NewGCMWithRandomNonce) function returns an [`AEAD`](/pkg/crypto/cipher#AEAD) that implements
AES-GCM by generating a random nonce during Seal and prepending it to the
ciphertext.

#### [`crypto/fips140`](/pkg/crypto/fips140/)

TODO: FIPS 140 will be covered in its own section.

#### [`crypto/md5`](/pkg/crypto/md5/)

The value returned by [`md5.New`](/pkg/md5#New) now also implements the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface.

#### [`crypto/rand`](/pkg/crypto/rand/)

The [`Read`](/pkg/crypto/rand#Read) function, and the `Read` method of [`Reader`](/pkg/crypto/rand#Reader), are now
defined to never fail.
They will always return `nil` as the `error` result.
If something somehow goes wrong while reading random numbers,
the program will irrecoverably crash.
This change was made because all supported systems now provide
sources of random bytes that never fail.

The new [`Text`](/pkg/crypto/rand#Text) function can be used to generate cryptographically secure random text strings. <!-- go.dev/issue/67057 -->

#### [`crypto/rsa`](/pkg/crypto/rsa/)

[`GenerateKey`](/pkg/crypto/rsa#GenerateKey) now returns an error if a key of less than 1024 bits is requested.
All Sign, Verify, Encrypt, and Decrypt methods now return an error if used with
a key smaller than 1024 bits. Such keys are insecure and should not be used.
Setting `GODEBUG=rsa1024min=0` or including `//go:debug rsa1024min=0` in a
source file restores the old behavior, but we recommend doing so only in tests,
if necessary. A new [`GenerateKey`](/pkg/crypto/rsa#GenerateKey) example provides an easy-to-use standard
2048-bit test key.

#### [`crypto/sha1`](/pkg/crypto/sha1/)

The value returned by [`sha1.New`](/pkg/sha1#New) now also implements the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface.

#### [`crypto/sha256`](/pkg/crypto/sha256/)

The values returned by [`sha256.New`](/pkg/sha256#New) and [`sha256.New224`](/pkg/sha256#New224) now also implement the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface

#### [`crypto/sha512`](/pkg/crypto/sha512/)

The values returned by [`sha512.New`](/pkg/sha512#New), [`sha512.New384`](/pkg/sha512#New384), [`sha512.New512_224`](/pkg/sha512#New512_224) and [`sha512.New512_256`](/pkg/sha512#New512_256) now also implement the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface.

#### [`crypto/subtle`](/pkg/crypto/subtle/)

The [`WithDataIndependentTiming`](/pkg/crypto/subtle#WithDataIndependentTiming) function allows the user to run a function with
architecture specific features enabled which guarantee specific instructions are
data value timing invariant. This can be used to make sure that code designed to
run in constant time is not optimized by CPU-level features such that it
operates in variable time. Currently, [`WithDataIndependentTiming`](/pkg/crypto/subtle#WithDataIndependentTiming) uses the
PSTATE.DIT bit on arm64, and is a no-op on all other architectures.

#### [`crypto/tls`](/pkg/crypto/tls/)

The [`ClientHelloInfo`](/pkg/crypto/tls#ClientHelloInfo) struct passed to [`Config.GetCertificate`](/pkg/crypto/tls#Config.GetCertificate) now includes an `Extensions` field, which can be useful for fingerprinting TLS clients.<!-- go.dev/issue/32936 -->

The TLS server now supports Encrypted Client Hello (ECH). This feature can be
enabled by populating the [`Config.EncryptedClientHelloKeys`](/pkg/crypto/tls#Config.EncryptedClientHelloKeys) field.

`crypto/tls` now supports the post-quantum [`X25519MLKEM768`](/pkg/crypto/tls#X25519MLKEM768) key exchange. Support
for the experimental X25519Kyber768Draft00 key exchange has been removed.

#### [`crypto/x509`](/pkg/crypto/x509/)

The `x509sha1` GODEBUG setting has been removed. [`Certificate.Verify`](/pkg/crypto/x509#Certificate.Verify) will no
longer consider SHA-1 based signatures valid when this GODEBUG setting is set.

[`OID`](/pkg/crypto/x509#OID) now implements the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) and [`encoding.TextAppender`](/pkg/encoding#TextAppender)
interfaces.

The default certificate policies field has changed from
[`Certificate.PolicyIdentifiers`](/pkg/crypto/x509#Certificate.PolicyIdentifiers) to [`Certificate.Policies`](/pkg/crypto/x509#Certificate.Policies). When parsing
certificates, both fields will be populated, but when creating certificates
policies will now be taken from the [`Certificate.Policies`](/pkg/crypto/x509#Certificate.Policies) field instead of the
[Certificate.PolicyIdentifiers field]. This change can be reverted by setting
`GODEBUG=x509usepolicies=0`.

[`CreateCertificate`](/pkg/crypto/x509#CreateCertificate) will now generate a serial number using a RFC 5280
compliant method when passed a template with a nil [`Certificate.SerialNumber`](/pkg/crypto/x509#Certificate.SerialNumber)
field, instead of failing.

[`Certificate.Verify`](/pkg/crypto/x509#Certificate.Verify) now supports policy validation, as defined by RFC 5280 and
RFC 9618. In order to enable policy validation,
[`VerifyOptions.CertificatePolicies`](/pkg/crypto/x509#VerifyOptions.CertificatePolicies) must be set to an acceptable set of policy
[`OIDs`](/pkg/crypto/x509#OIDs). When enabled, only certificate chains with valid policy graphs will be
returned from [`Certificate.Verify`](/pkg/crypto/x509#Certificate.Verify).

[`MarshalPKCS8PrivateKey`](/pkg/crypto/x509#MarshalPKCS8PrivateKey) now returns an error instead of marshaling an invalid
RSA key. ([`MarshalPKCS1PrivateKey`](/pkg/crypto/x509#MarshalPKCS1PrivateKey) doesn't have an error return, and its behavior
when provided invalid keys continues to be undefined.)

[`ParsePKCS1PrivateKey`](/pkg/crypto/x509#ParsePKCS1PrivateKey) and [`ParsePKCS8PrivateKey`](/pkg/crypto/x509#ParsePKCS8PrivateKey) now use and validate the
encoded CRT values, so might reject invalid keys that were previously accepted.
Use `GODEBUG=x509rsacrt=0` to revert to recomputing them.

#### [`debug/elf`](/pkg/debug/elf/)

The [`debug/elf`](/pkg/debug/elf) package adds several new constants, types, and methods to add support for handling dynamic versions and version flags in ELF (Executable and Linkable Format) files:

Several new types have been introduced:
- [`DynamicVersion`](/pkg/debug/elf#DynamicVersion) struct represents a dynamic version entry in the ELF file.
- [`DynamicVersionDep`](/pkg/debug/elf#DynamicVersionDep) struct represents a dependency of a dynamic version.
- [`DynamicVersionNeed`](/pkg/debug/elf#DynamicVersionNeed) struct represents a required dynamic version in the ELF file.
- [`DynamicVersionFlag`](/pkg/debug/elf#DynamicVersionFlag) is a new type defined as uint16, representing flags for dynamic versions.
    - [`VER_FLG_BASE`](/pkg/debug/elf#VER_FLG_BASE) version definition of the file.
    - [`VER_FLG_WEAK`](/pkg/debug/elf#VER_FLG_WEAK) weak version identifier.
    - [`VER_FLG_INFO`](/pkg/debug/elf#VER_FLG_INFO) reference exists for informational purposes.
- [`SymbolVersionFlag`](/pkg/debug/elf#SymbolVersionFlag) is a new type defined as uint8, representing version flags for ELF symbols.
    - [`VerFlagNone`](/pkg/debug/elf#VerFlagNone) no flags.
    - [`VerFlagLocal`](/pkg/debug/elf#VerFlagLocal) symbol has local scope.
    - [`VerFlagGlobal`](/pkg/debug/elf#VerFlagGlobal) symbol has global scope.
    - [`VerFlagHidden`](/pkg/debug/elf#VerFlagHidden) symbol is hidden.

The following methods have been added:
- [`File.DynamicVersionNeeds`](/pkg/debug/elf#File.DynamicVersionNeeds) method returns a list of dynamic version needs in the ELF file, representing dependencies required by the executable.
- [`File.DynamicVersions`](/pkg/debug/elf#File.DynamicVersions) retrieves a list of dynamic versions defined in the ELF file.
<!-- go.dev/issue/63952 -->

#### [`encoding`](/pkg/encoding/)

Two new interfaces, [`TextAppender`](/pkg/encoding#TextAppender) and [`BinaryAppender`](/pkg/encoding#BinaryAppender), have been
introduced to append the textual or binary representation of an object
to a byte slice. These interfaces provide the same functionality as
[`TextMarshaler`](/pkg/encoding#TextMarshaler) and [`BinaryMarshaler`](/pkg/encoding#BinaryMarshaler), but instead of allocating a new slice
each time, they append the data directly to an existing slice.

#### [`encoding/json`](/pkg/encoding/json/)

When marshaling, a struct field with the new `omitzero` option in the struct field
tag will be omitted if its value is zero. If the field type has an `IsZero() bool`
method, that will be used to determine whether the value is zero. Otherwise, the
value is zero if it is [the zero value for its type](/ref/spec#The_zero_value).

If both `omitempty` and `omitzero` are specified, the field will be omitted if the
value is either empty or zero (or both).

[`UnmarshalTypeError.Field`](/pkg/encoding/json#UnmarshalTypeError.Field) now includes embedded structs to provide more detailed error messages.

#### [`go/types`](/pkg/go/types/)

All `go/types` data structures that expose sequences using a pair of
methods such as `Len() int` and `At(int) T` now also have methods that
return iterators, allowing you to simplify code such as this:

```
params := fn.Type.(*types.Signature).Params()
for i := 0; i < params.Len(); i++ {
   use(params.At(i))
}
```

to this:

```
for param := range fn.Signature().Params().Variables() {
   use(param)
}
```

The methods are:
[`Interface.EmbeddedTypes`](/pkg/go/types#Interface.EmbeddedTypes),
[`Interface.ExplicitMethods`](/pkg/go/types#Interface.ExplicitMethods),
[`Interface.Methods`](/pkg/go/types#Interface.Methods),
[`MethodSet.Methods`](/pkg/go/types#MethodSet.Methods),
[`Named.Methods`](/pkg/go/types#Named.Methods),
[`Scope.Children`](/pkg/go/types#Scope.Children),
[`Struct.Fields`](/pkg/go/types#Struct.Fields),
[`Tuple.Variables`](/pkg/go/types#Tuple.Variables),
[`TypeList.Types`](/pkg/go/types#TypeList.Types),
[`TypeParamList.TypeParams`](/pkg/go/types#TypeParamList.TypeParams),
[`Union.Terms`](/pkg/go/types#Union.Terms).

#### [`hash/adler32`](/pkg/hash/adler32/)

The value returned by [`New`](/pkg/hash/adler32#New) now also implements the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface.

#### [`hash/crc32`](/pkg/hash/crc32/)

The values returned by [`New`](/pkg/hash/crc32#New) and [`NewIEEE`](/pkg/hash/crc32#NewIEEE) now also implement the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface.

#### [`hash/crc64`](/pkg/hash/crc64/)

The value returned by [`New`](/pkg/hash/crc64#New) now also implements the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface.

#### [`hash/fnv`](/pkg/hash/fnv/)

The values returned by [`New32`](/pkg/hash/fnv#New32), [`New32a`](/pkg/hash/fnv#New32a), [`New64`](/pkg/hash/fnv#New64), [`New64a`](/pkg/hash/fnv#New64a), [`New128`](/pkg/hash/fnv#New128) and [`New128a`](/pkg/hash/fnv#New128a) now also implement the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface.

#### [`hash/maphash`](/pkg/hash/maphash/)

New function [`Comparable`](/pkg/hash/maphash#Comparable) returns the hash of comparable value v.
New function [`WriteComparable`](/pkg/hash/maphash#WriteComparable) adds x to the data hashed by [`Hash`](/pkg/hash/maphash#Hash).

#### [`log/slog`](/pkg/log/slog/)

The new [`DiscardHandler`](/pkg/log/slog#DiscardHandler) is a handler that is never enabled and always discards its output.

[`Level`](/pkg/log/slog#Level) and [`LevelVar`](/pkg/log/slog#LevelVar) now implement the [`encoding.TextAppender`](/pkg/encoding#TextAppender) interface.

#### [`math/big`](/pkg/math/big/)

[`Float`](/pkg/math/big#Float), [`Int`](/pkg/math/big#Int) and [`Rat`](/pkg/math/big#Rat) now implement the [`encoding.TextAppender`](/pkg/encoding#TextAppender) interface.

#### [`math/rand`](/pkg/math/rand/)

Calls to the deprecated top-level [`Seed`](/pkg/math/rand#Seed) function no longer have any effect. To
restore the old behavior set `GODEBUG=randseednop=0`. For more background see
the proposal [#67273](/issue/67273).

#### [`math/rand/v2`](/pkg/math/rand/v2/)

[`ChaCha8`](/pkg/math/rand/v2#ChaCha8) and [`PCG`](/pkg/math/rand/v2#PCG) now implement the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface.

#### [`net`](/pkg/net/)

[`ListenConfig`](/pkg/net#ListenConfig) now uses MPTCP by default on systems where it is supported
(currently on Linux only).

[`IP`](/pkg/net#IP) now implements the [`encoding.TextAppender`](/pkg/encoding#TextAppender) interface.

#### [`net/http`](/pkg/net/http/)

[`Transport`](/pkg/net/http#Transport)'s limit on 1xx informational responses received
in response to a request has changed.
It previously aborted a request and returned an error after
receiving more than 5 1xx responses.
It now returns an error if the total size of all 1xx responses
exceeds the [`Transport.MaxResponseHeaderBytes`](/pkg/net/http#Transport.MaxResponseHeaderBytes) configuration setting.

In addition, when a request has a
[`net/http/httptrace.ClientTrace.Got1xxResponse`](/pkg/net/http/httptrace#ClientTrace.Got1xxResponse)
trace hook, there is now no limit on the total number of 1xx responses.
The `Got1xxResponse` hook may return an error to abort a request.

[`Transport`](/pkg/net/http#Transport) and [`Server`](/pkg/net/http#Server) now have an HTTP2 field which permits
configuring HTTP/2 protocol settings.

The new [`Server.Protocols`](/pkg/net/http#Server.Protocols) and [`Transport.Protocols`](/pkg/net/http#Transport.Protocols) fields provide
a simple way to configure what HTTP protocols a server or client use.

The server and client may be configured to support unencrypted HTTP/2
connections.

When [`Server.Protocols`](/pkg/net/http#Server.Protocols) contains UnencryptedHTTP2, the server will accept
HTTP/2 connections on unencrypted ports. The server can accept both
HTTP/1 and unencrypted HTTP/2 on the same port.

When [`Transport.Protocols`](/pkg/net/http#Transport.Protocols) contains UnencryptedHTTP2 and does not contain
HTTP1, the transport will use unencrypted HTTP/2 for http:// URLs.
If the transport is configured to use both HTTP/1 and unencrypted HTTP/2,
it will use HTTP/1.

Unencrypted HTTP/2 support uses "HTTP/2 with Prior Knowledge"
(RFC 9113, section 3.3). The deprecated "Upgrade: h2c" header
is not supported.

#### [`net/netip`](/pkg/net/netip/)

[`Addr`](/pkg/net/netip#Addr), [`AddrPort`](/pkg/net/netip#AddrPort) and [`Prefix`](/pkg/net/netip#Prefix) now implement the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) and
[`encoding.TextAppender`](/pkg/encoding#TextAppender) interfaces.

#### [`net/url`](/pkg/net/url/)

[`URL`](/pkg/net/url#URL) now also implements the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) interface.

#### [`os/user`](/pkg/os/user/)

On Windows, [`Current`](/pkg/os/user#Current) can now be used in Windows Nano Server.
The implementation has been updated to avoid using functions
from the `NetApi32` library, which is not available in Nano Server.

On Windows, [`Current`](/pkg/os/user#Current), [`Lookup`](/pkg/os/user#Lookup) and [`LookupId`](/pkg/os/user#LookupId) now supports the
following built-in service user accounts:
- `NT AUTHORITY\SYSTEM`
- `NT AUTHORITY\LOCAL SERVICE`
- `NT AUTHORITY\NETWORK SERVICE`

On Windows, [`Current`](/pkg/os/user#Current) has been made considerably faster when
the current user is joined to a slow domain, which is the
usual case for many corporate users. The new implementation
performance is now in the order of milliseconds, compared to
the previous implementation which could take several seconds,
or even minutes, to complete.

On Windows, [`Current`](/pkg/os/user#Current) now returns the process owner user when
the current thread is impersonating another user. Previously,
it returned an error.

#### [`regexp`](/pkg/regexp/)

[`Regexp`](/pkg/regexp#Regexp) now implements the [`encoding.TextAppender`](/pkg/encoding#TextAppender) interface.

#### [`runtime`](/pkg/runtime/)

The [`GOROOT`](/pkg/runtime#GOROOT) function is now deprecated.
In new code prefer to use the system path to locate the “go” binary,
and use `go env GOROOT` to find its GOROOT.

The [`AddCleanup`](/pkg/runtime#AddCleanup) function attaches a function to a pointer. Once the object that
the pointer points to is no longer reachable, the runtime will call the function.
[`AddCleanup`](/pkg/runtime#AddCleanup) is a finalization mechanism similar to [`SetFinalizer`](/pkg/runtime#SetFinalizer). Unlike
[`SetFinalizer`](/pkg/runtime#SetFinalizer), it does not resurrect objects while running the cleanup. Multiple
cleanups can be attached to a single object. [`AddCleanup`](/pkg/runtime#AddCleanup) is an improvement over
[`SetFinalizer`](/pkg/runtime#SetFinalizer).

#### [`strings`](/pkg/strings/)

The [`strings`](/pkg/strings) package adds several functions that work with iterators:
- [`Lines`](/pkg/strings#Lines) returns an iterator over
  the newline-terminated lines in the string s.
- [`SplitSeq`](/pkg/strings#SplitSeq) returns an iterator over
  all substrings of s separated by sep.
- [`SplitAfterSeq`](/pkg/strings#SplitAfterSeq) returns an iterator
  over substrings of s split after each instance of sep.
- [`FieldsSeq`](/pkg/strings#FieldsSeq) returns an iterator over
  substrings of s split around runs of whitespace characters,
  as defined by unicode.IsSpace.
- [`FieldsFuncSeq`](/pkg/strings#FieldsFuncSeq) returns an iterator
  over substrings of s split around runs of Unicode code points satisfying f(c).

#### [`sync`](/pkg/sync/)

The implementation of [`sync.Map`](/pkg/sync#Map) has been changed, improving overall performance
and resolving some long-standing issues.
If you encounter any problems, set `GOEXPERIMENT=nosynchashtriemap` at build
time to switch back to the old implementation and please [file an
issue](/issue/new).

#### [`testing`](/pkg/testing/)

The new [`T.Context`](/pkg/testing#T.Context) and [`B.Context`](/pkg/testing#B.Context) methods return a context that's canceled
after the test completes and before test cleanup functions run.

<!-- testing.B.Loop mentioned in 6-stdlib/6-testing-bloop.md. -->

The new [`T.Chdir`](/pkg/testing#T.Chdir) and [`B.Chdir`](/pkg/testing#B.Chdir) methods can be used to change the working
directory for the duration of a test or benchmark.

#### [`text/template`](/pkg/text/template/)

Templates now support range-over-func and range-over-int.

#### [`time`](/pkg/time/)

[`Time`](/pkg/time#Time) now implements the [`encoding.BinaryAppender`](/pkg/encoding#BinaryAppender) and [`encoding.TextAppender`](/pkg/encoding#TextAppender) interfaces.

## Ports {#ports}

### Linux {#linux}

<!-- go.dev/issue/67001 -->
As [announced](go1.23#linux) in the Go 1.23 release notes, Go 1.24 requires Linux
kernel version 3.2 or later.

### Darwin {#darwin}

<!-- go.dev/issue/69839 -->
Go 1.24 is the last release that will run on macOS 11 Big Sur.
Go 1.25 will require macOS 12 Monterey or later.

### WebAssembly {#wasm}

<!-- go.dev/issue/65199, CL 603055 -->
The `go:wasmexport` directive is added for Go programs to export functions to the WebAssembly host.

On WebAssembly System Interface Preview 1 (`GOOS=wasip1, GOARCH=wasm`), Go 1.24 supports
building a Go program as a
[reactor/library](https://github.com/WebAssembly/WASI/blob/63a46f61052a21bfab75a76558485cf097c0dbba/legacy/application-abi.md#current-unstable-abi),
by specifying the `-buildmode=c-shared` build flag.

<!-- go.dev/issue/66984, CL 626615 -->
More types are now permitted as argument or result types for `go:wasmimport` functions.
Specifically, `bool`, `string`, `uintptr`, and pointers to certain types are allowed
(see the [proposal](/issue/66984) for detail),
along with 32-bit and 64-bit integer and float types, and `unsafe.Pointer`, which
are already allowed.
These types are also permitted as argument or result types for `go:wasmexport` functions.

<!-- go.dev/issue/68024 -->
The support files for WebAssembly have been moved to `lib/wasm` from `misc/wasm`.

### Windows {#windows}

<!-- go.dev/issue/70705 -->
The windows/arm port (`GOOS=windows` `GOARCH=arm`) has been marked broken.
See [issue 70705](/issue/70705) for details.

<!-- Needs to be documented and tracked via a release-blocking issue.

accepted proposal https://go.dev/issue/26232 (from https://go.dev/cl/605256, https://go.dev/cl/605275, https://go.dev/cl/605298, https://go.dev/cl/625036) - cmd/go's HTTP auth is tracked in proposal 26232 itself as a release blocker
accepted proposal https://go.dev/issue/50603 (from https://go.dev/cl/595376, https://go.dev/cl/596035, https://go.dev/cl/609155, https://go.dev/cl/611916, https://go.dev/cl/627295) - cmd/go support for stamping pseudo-version in go build is tracked in proposal 50603 itself as a release blocker
accepted proposal https://go.dev/issue/69393 (from https://go.dev/cl/630775) - automatic crypto/tls.CurvePreferences ordering is now tracked in proposal 69393 itself as a release blocker
-->

<!-- Needs to be documented, but not currently tracked via a release-blocking issue.

accepted proposal https://go.dev/issue/66821 (from https://go.dev/cl/602495, https://go.dev/cl/602497, https://go.dev/cl/608175, https://go.dev/cl/608435, https://go.dev/cl/621979, https://go.dev/cl/622115) - crashing the process on error reading randomness (which should not have a path to happen) might need to be mentioned; commented at https://go.dev/issues/66821#issuecomment-2502069725 for next steps; Ian sent out CL 632036
-->

<!-- Maybe worth including or maybe fine not to include in Go 1.24 release notes. Someone more familiar with the change makes the call.

accepted proposal https://go.dev/issue/64802 (from https://go.dev/cl/628681) - a crypto/ecdsa change when rand is nil; commented at https://go.dev/issue/64802#issuecomment-2502019212 for next steps
accepted proposal https://go.dev/issue/25309 (from https://go.dev/cl/594018, https://go.dev/cl/595120, https://go.dev/cl/595564, https://go.dev/cl/601778) - new x/crypto package; doesn't seem to need to be mentioned but asked anyway in https://go.dev/issue/25309#issuecomment-2498747653
accepted proposal https://go.dev/issue/43744 (from https://go.dev/cl/357530) - unclear if Go 1.24 release notes need anything; pinged it in https://go.dev/issue/43744#issuecomment-2498773718
accepted proposal https://go.dev/issue/69687 (from https://go.dev/cl/591997, https://go.dev/cl/629735) - experimental package testing/synctest behind an experiment; commented at https://github.com/golang/go/issues/69687#issuecomment-2502179333, leaving to Damien to decide whether to document it or defer that until the package is added as non-experiment
accepted proposal https://go.dev/issue/51269 (from https://go.dev/cl/627035) - may be worth mentioning in Go 1.24 release notes, or may be fine to leave out; commented at https://go.dev/issue/51269#issuecomment-2501802763
accepted proposal https://go.dev/issue/60905 (from https://go.dev/cl/610195) - CL 610195 seems like a small performance enhancement that builds on the Go 1.23 proposal to add GOARM64; probably okay without being mentioned in Go 1.24 release notes (also probably okay to mention)
accepted proposal https://go.dev/issue/61395 (from https://go.dev/cl/594738, https://go.dev/cl/594976) - CL 594738 made sync/atomic AND/OR operations intrinsic on amd64, but the API was already added in Go 1.23; CL 594976 is a fix; probably doesn't require a Go 1.24 release note
-->

<!-- Items that don't need to be mentioned in Go 1.24 release notes but are picked up by relnote todo.

accepted proposal https://go.dev/issue/66540 (from https://go.dev/cl/603958) - a Go language spec clarification; might not need to be mentioned in Go 1.24 release notes; left a comment at https://go.dev/issue/66540#issuecomment-2502051684; Robert confirmed it indeed doesn't
accepted proposal https://go.dev/issue/34208 (from https://go.dev/cl/586241) - CL 586241 implements a fix for a Go 1.23 feature, doesn't seem to be need anything in Go 1.24 release notes
accepted proposal https://go.dev/issue/43993 (from https://go.dev/cl/626116) - CL 626116 prepares the tree towards the vet change but the vet change itself isn't implemented in Go 1.24, so nothing to say in Go 1.24 release notes
accepted proposal https://go.dev/issue/44505 (from https://go.dev/cl/609955) - CL 609955 is an internal cleanup in x/tools, no need for Go 1.24 release note
accepted proposal https://go.dev/issue/61476 (from https://go.dev/cl/608255) - CL 608255 builds on GORISCV64 added in Go 1.23; nothing to mention in Go 1.24 release notes
accepted proposal https://go.dev/issue/66315 (from https://go.dev/cl/577996) - adding Pass.Module field to x/tools/go/analysis doesn't seem like something that needs to be mentioned in Go 1.24 release notes
accepted proposal https://go.dev/issue/57786 (from https://go.dev/cl/472717) - CL 472717 is in x/net/http2 and mentions a Go 1.21 proposal; it doesn't seem to need anything in Go 1.24 release notes
accepted proposal https://go.dev/issue/54265 (from https://go.dev/cl/609915, https://go.dev/cl/610675) - CLs that refer to a Go 1.22 proposal, nothing more is needed in Go 1.24 release notes
accepted proposal https://go.dev/issue/53021 (from https://go.dev/cl/622276) - CL 622276 improves docs; proposal 53021 was in Go 1.20 so nothing more is needed in Go 1.24 release notes
accepted proposal https://go.dev/issue/51430 (from https://go.dev/cl/613375) - CL 613375 is an internal documentation comment; proposal 51430 happened in Go 1.20/1.21 so nothing more is needed in Go 1.24 release notes
accepted proposal https://go.dev/issue/38445 (from https://go.dev/cl/626495) - CL 626495 works on proposal 38445, which is about x/tools/go/package, doesn't need anything in Go 1.24 release notes
accepted proposal https://go.dev/issue/56986 (from https://go.dev/cl/618115) - CL 618115 adds documentation; it doesn't need to be mentioned in Go 1.24 release notes
accepted proposal https://go.dev/issue/60061 (from https://go.dev/cl/612038) - CL 612038 is a CL that deprecates something in x/tools/go/ast and mentions a Go 1.22 proposal; doesn't need anything in Go 1.24 release notes
accepted proposal https://go.dev/issue/61324 (from https://go.dev/cl/411907) - CL 411907 is an x/tools CL that implements a proposal for a new package there; doesn't need anything in Go 1.24 release notes
accepted proposal https://go.dev/issue/61777 (from https://go.dev/cl/601496) - CL 601496 added a WriteByteTimeout field to x/net/http2.Server; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/61940 (from https://go.dev/cl/600997) - CL 600997 deleted obsolete code in x/build and mentioned an accepted proposal; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/62113 (from https://go.dev/cl/594195) - CL 594195 made iterator-related additions in x/net/html; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/62484 (from https://go.dev/cl/600775) - CL 600775 documents CopyFS symlink behavior and mentions the Go 1.23 proposal; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/64207 (from https://go.dev/cl/605875) - an x/website CL that follows up on a Go 1.23 proposal; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/65236 (from https://go.dev/cl/596135) - CL 596135 adds tests for the Go 1.23 proposal 65236; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/67795 (from https://go.dev/cl/616218) - iteratior support for x/tools/go/ast/inspector; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/67812 (from https://go.dev/cl/601497) - configurable server pings for x/net/http2.Server; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/68232 (from https://go.dev/cl/595676) - x/sys/unix additions; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/68898 (from https://go.dev/cl/607495, https://go.dev/cl/620036, https://go.dev/cl/620135, https://go.dev/cl/623638) - a proposal for x/tools/go/gcexportdata to document 2 releases + tip support policy; since the change is in x/tools it doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/69095 (from https://go.dev/cl/593683, https://go.dev/cl/608955, https://go.dev/cl/610716) - a proposal that affects maintenance and support of golang.org/x repositories; doesn't need to be mentioned in Go 1.24 release notes
accepted proposal https://go.dev/issue/68384 (from https://go.dev/cl/611875) - expanding the scope of Go Telemetry to include Delve isn't directly tied to Go 1.24 and doesn't seem to need to be mentioned in Go 1.24 release notes
accepted proposal https://go.dev/issue/69291 (from https://go.dev/cl/610939) - CL 610939 refactors code in x/tools and mentions the still-open proposal #69291 to add Reachable to x/tools/go/ssa/ssautil; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/69360 (from https://go.dev/cl/614158, https://go.dev/cl/614159, https://go.dev/cl/614635, https://go.dev/cl/614675) - proposal 69360 is to tag and delete gorename from x/tools; doesn't need a Go 1.24 release note
accepted proposal https://go.dev/issue/61417 (from https://go.dev/cl/605955) - a new field in x/oauth2; nothing to mention in Go 1.24 release notes
-->