_content/doc/go1.23.md

---
title: Go 1.23 Release Notes
template: false
---

<!--
NOTE: In this document and others in this directory, the convention is to
set fixed-width phrases with non-fixed-width spaces, as in
`hello` `world`.
-->

<style>
  main ul li { margin: 0.5em 0; }
</style>

## Introduction to Go 1.23 {#introduction}

The latest Go release, version 1.23, arrives six months after [Go 1.22](/doc/go1.22).
Most of its changes are in the implementation of the toolchain, runtime, and libraries.
As always, the release maintains the Go 1 [promise of compatibility](/doc/go1compat).
We expect almost all Go programs to continue to compile and run as before.

## Changes to the language {#language}

<!-- go.dev/issue/61405, CL 557835, CL 584596 -->
The "range" clause in a "for-range" loop now accepts iterator functions of the following types

    func(func() bool)
    func(func(K) bool)
    func(func(K, V) bool)

as range expressions.
Calls of the iterator argument function produce the iteration values for the "for-range" loop.
For details see the [`iter`](/pkg/iter) package documentation, the
[language spec](/ref/spec#For_range), and the [Range over Function
Types blog post](/blog/range-functions).
For motivation see the 2022 ["range-over-func" discussion](/issue/56413).

<!-- go.dev/issue/46477, CL 566856, CL 586955, CL 586956 -->
Go 1.23 includes preview support for [generic type aliases](/issue/46477).
Building the toolchain with `GOEXPERIMENT=aliastypeparams` enables this feature within a package.
(Using generic alias types across package boundaries is not yet supported.)

## Tools {#tools}

### Telemetry

<!-- go.dev/issue/58894, go.dev/issue/67111 -->
Starting in Go 1.23, the Go toolchain can collect usage and breakage
statistics that help the Go team understand how the Go toolchain is
used and how well it is working. We refer to these statistics as
[Go telemetry](/doc/telemetry).

Go telemetry is an _opt-in system_, controlled by the
[`go` `telemetry` command](/cmd/go/#hdr-Manage_telemetry_data_and_settings).
By default, the toolchain programs
collect statistics in counter files that can be inspected locally
but are otherwise unused (`go` `telemetry` `local`).

To help us keep Go working well and understand Go usage,
please consider opting in to Go telemetry by running
`go` `telemetry` `on`.
In that mode,
anonymous counter reports are uploaded to
[telemetry.go.dev](https://telemetry.go.dev) weekly,
where they are aggregated into graphs and also made
available for download by any Go contributors or users
wanting to analyze the data.
See “[Go Telemetry](/doc/telemetry)” for more details
about the Go Telemetry system.

### Go command {#go-command}

Setting the `GOROOT_FINAL` environment variable no longer has an effect
([#62047](/issue/62047)).
Distributions that install the `go` command to a location other than
`$GOROOT/bin/go` should install a symlink instead of relocating
or copying the `go` binary.

<!-- go.dev/issue/34208, CL 563137, CL 586095 -->
The new `go` `env` `-changed` flag causes the command to print only
those settings whose effective value differs from the default value
that would be obtained in an empty environment with no prior uses of the `-w` flag.

<!-- go.dev/issue/27005, CL 585401 -->
The new `go` `mod` `tidy` `-diff` flag causes the command not to modify
the files but instead print the necessary changes as a unified diff.
It exits with a non-zero code if updates are needed.

<!-- go.dev/issue/52792, CL 562775 -->
The `go` `list` `-m` `-json` command now includes new `Sum` and `GoModSum` fields.
This is similar to the existing behavior of the `go` `mod` `download` `-json` command.

<!-- go.dev/issue/65573 ("cmd/go: separate default GODEBUGs from go language version") -->
The new `godebug` directive in `go.mod` and `go.work` declares a
[GODEBUG setting](/doc/godebug) to apply for the work module or workspace in use.

### Vet {#vet}

<!-- go.dev/issue/46136 -->
The `go vet` subcommand now includes the
[stdversion](https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/stdversion)
analyzer, which flags references to symbols that are too new for the version
of Go in effect in the referring file. (The effective version is determined
by the `go` directive in the file's enclosing `go.mod` file, and
by any [`//go:build` constraints](/cmd/go#hdr-Build_constraints)
in the file.)

For example, it will report a diagnostic for a reference to the
`reflect.TypeFor` function (introduced in go1.22) from a file in a
module whose go.mod file specifies `go 1.21`.

### Cgo {#cgo}

<!-- go.dev/issue/66456 -->
[`cmd/cgo`](/pkg/cmd/cgo) supports the new `-ldflags` flag for passing flags to the C linker.
The `go` command uses it automatically, avoiding "argument list too long"
errors with a very large `CGO_LDFLAGS`.

### Trace {#trace}

<!-- go.dev/issue/65316 -->
The `trace` tool now better tolerates partially broken traces by attempting to
recover what trace data it can. This functionality is particularly helpful when
viewing a trace that was collected during a program crash, since the trace data
leading up to the crash will now [be recoverable](/issue/65319) under most
circumstances.

## Runtime {#runtime}

The traceback printed by the runtime after an unhandled panic or other
fatal error now indents the second and subsequent lines of the error
message (for example, the argument to panic) by a single tab, so that
it can be unambiguously distinguished from the stack trace of the
first goroutine. See [#64590](/issue/64590) for discussion.

## Compiler {#compiler}

The build time overhead to building with [Profile Guided Optimization](/doc/pgo) has been reduced significantly.
Previously, large builds could see 100%+ build time increase from enabling PGO.
In Go 1.23, overhead should be in the single digit percentages.

<!-- https://go.dev/issue/62737 , https://golang.org/cl/576681,  https://golang.org/cl/577615 -->
The compiler in Go 1.23 can now overlap the stack frame slots of local variables
accessed in disjoint regions of a function, which reduces stack usage
for Go applications.

<!-- https://go.dev/cl/577935 -->
For 386 and amd64, the compiler will use information from PGO to align certain
hot blocks in loops.  This improves performance an additional 1-1.5% at
a cost of an additional 0.1% text and binary size.  This is currently only implemented
on 386 and amd64 because it has not shown an improvement on other platforms.
Hot block alignment can be disabled with `-gcflags=[<packages>=]-d=alignhot=0`.

## Linker {#linker}

<!-- go.dev/issue/67401, CL 585556, CL 587220, and many more -->
The linker now disallows using a `//go:linkname` directive to refer to
internal symbols in the standard library (including the runtime) that
are not marked with `//go:linkname` on their definitions.
Similarly, the linker disallows references to such symbols from assembly
code.
For backward compatibility, existing usages of `//go:linkname` found in
a large open-source code corpus remain supported.
Any new references to standard library internal symbols will be disallowed.

A linker command line flag `-checklinkname=0` can be used to disable
this check, for debugging and experimenting purposes.

<!-- CL 473495 -->
When building a dynamically linked ELF binary (including PIE binary), the
new `-bindnow` flag enables immediate function binding.

## Standard library {#library}

### Timer changes

Go 1.23 makes two significant changes to the implementation of
[`time.Timer`](/pkg/time#Timer) and [`time.Ticker`](/pkg/time#Ticker).

<!-- go.dev/issue/61542 -->
First, `Timer`s and `Ticker`s that are no longer referred to by the program
become eligible for garbage collection immediately, even if their
`Stop` methods have not been called.
Earlier versions of Go did not collect unstopped `Timer`s until after
they had fired and never collected unstopped `Ticker`s.

<!-- go.dev/issue/37196 -->
Second, the timer channel associated with a `Timer` or `Ticker` is
now unbuffered, with capacity 0.
The main effect of this change is that Go now guarantees
that for any call to a `Reset` or `Stop` method, no stale values
prepared before that call will be sent or received after the call.
Earlier versions of Go used channels with a one-element buffer,
making it difficult to use `Reset` and `Stop` correctly.
A visible effect of this change is that `len` and `cap` of timer channels
now returns 0 instead of 1, which may affect programs that
poll the length to decide whether a receive on the timer channel
will succeed.
Such code should use a non-blocking receive instead.

These new behaviors are only enabled when the main Go program
is in a module with a `go.mod` `go` line using Go 1.23.0 or later.
When Go 1.23 builds older programs, the old behaviors remain in effect.
The new [GODEBUG setting](/doc/godebug) [`asynctimerchan=1`](/pkg/time/#NewTimer)
can be used to revert back to asynchronous channel behaviors
even when a program names Go 1.23.0 or later in its `go.mod` file.

### New unique package

The new [`unique`](/pkg/unique) package provides facilities for
canonicalizing values (like "interning" or "hash-consing").

Any value of comparable type may be canonicalized with the new
`Make[T]` function, which produces a reference to a canonical copy of
the value in the form of a `Handle[T]`.
Two `Handle[T]` are equal if and only if the values used to produce the
handles are equal, allowing programs to deduplicate values and reduce
their memory footprint.
Comparing two `Handle[T]` values is efficient, reducing down to a simple
pointer comparison.

### Iterators

The new [`iter`](/pkg/iter) package provides the basic definitions for working with
user-defined iterators.

The [`slices`](/pkg/slices) package adds several functions that work with iterators:
- [All](/pkg/slices#All) returns an iterator over slice indexes and values.
- [Values](/pkg/slices#Values) returns an iterator over slice elements.
- [Backward](/pkg/slices#Backward) returns an iterator that loops over
  a slice backward.
- [Collect](/pkg/slices#Collect) collects values from an iterator into
  a new slice.
- [AppendSeq](/pkg/slices#AppendSeq) appends values from an iterator to
  an existing slice.
- [Sorted](/pkg/slices#Sorted) collects values from an iterator into a
  new slice, and then sorts the slice.
- [SortedFunc](/pkg/slices#SortedFunc) is like `Sorted` but with a
  comparison function.
- [SortedStableFunc](/pkg/slices#SortedStableFunc) is like `SortFunc`
  but uses a stable sort algorithm.
- [Chunk](/pkg/slices#Chunk) returns an iterator over consecutive
  sub-slices of up to n elements of a slice.

The [`maps`](/pkg/maps) package adds several functions that work with iterators:
- [All](/pkg/maps#All) returns an iterator over key-value pairs from a map.
- [Keys](/pkg/maps#Keys) returns an iterator over keys in a map.
- [Values](/pkg/maps#Values) returns an iterator over values in a map.
- [Insert](/pkg/maps#Insert) adds the key-value pairs from an iterator to an existing map.
- [Collect](/pkg/maps#Collect) collects key-value pairs from an iterator into a new map and returns it.

### New structs package

The new [`structs`](/pkg/structs) package provides
types for struct fields that modify properties of
the containing struct type such as memory layout.

In this release, the only such type is
[`HostLayout`](/pkg/structs#HostLayout)
which indicates that a structure with a field of that
type has a layout that conforms to host platform
expectations.  HostLayout should be used in types that
are passed to, returned from, or accessed
via a pointer passed to/from host APIs.
Without this marker, struct layout order is not
guaranteed by the language spec, though as of Go 1.23
the host and language layouts happen to match.

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

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

If the argument to [`FileInfoHeader`](/pkg/archive/tar#FileInfoHeader) implements the new [`FileInfoNames`](/pkg/archive/tar#FileInfoNames)
interface, then the interface methods will be used to set the Uname/Gname
of the file header. This allows applications to override the system-dependent
Uname/Gname lookup.

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

The TLS client now supports the Encrypted Client Hello [draft specification](https://www.ietf.org/archive/id/draft-ietf-tls-esni-18.html).
This feature can be enabled by setting the [`Config.EncryptedClientHelloConfigList`](/pkg/crypto/tls#Config.EncryptedClientHelloConfigList)
field to an encoded ECHConfigList for the host that is being connected to.

The [`QUICConn`](/pkg/crypto/tls#QUICConn) type used by QUIC implementations includes new events
reporting on the state of session resumption, and provides a way for
the QUIC layer to add data to session tickets and session cache entries.

3DES cipher suites were removed from the default list used when
[`Config.CipherSuites`](/pkg/crypto/tls#Config.CipherSuites) is nil. The default can be reverted by adding `tls3des=1` to
the GODEBUG environment variable.

The experimental post-quantum key exchange mechanism X25519Kyber768Draft00
is now enabled by default when [`Config.CurvePreferences`](/pkg/crypto/tls#Config.CurvePreferences) is nil.
The default can be reverted by adding `tlskyber=0` to the GODEBUG environment variable.

Go 1.23 changed the behavior of [`X509KeyPair`](/pkg/crypto/tls#X509KeyPair) and [`LoadX509KeyPair`](/pkg/crypto/tls#LoadX509KeyPair)
to populate the [`Certificate.Leaf`](/pkg/crypto/tls#Certificate.Leaf) field of the returned [`Certificate`](/pkg/crypto/tls#Certificate).
The new `x509keypairleaf` [GODEBUG setting](/doc/godebug) is added for this behavior.

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

[`CreateCertificateRequest`](/pkg/crypto/x509#CreateCertificateRequest) now correctly supports RSA-PSS signature algorithms.

[`CreateCertificateRequest`](/pkg/crypto/x509#CreateCertificateRequest) and [`CreateRevocationList`](/pkg/crypto/x509#CreateRevocationList) now verify the generated signature using the signer’s public key. If the signature is invalid, an error is returned. This has been the behavior of [`CreateCertificate`](/pkg/crypto/x509#CreateCertificate) since Go 1.16.

The [`x509sha1` GODEBUG setting](/pkg/crypto/x509#InsecureAlgorithmError) will
be removed in the next Go major release (Go 1.24). This will mean that `crypto/x509`
will no longer support verifying signatures on certificates that use SHA-1 based
signature algorithms.

The new [`ParseOID`](/pkg/crypto/x509#ParseOID) function parses a dot-encoded ASN.1 Object Identifier string.
The [`OID`](/pkg/crypto/x509#OID) type now implements the [`encoding.BinaryMarshaler`](/pkg/encoding#BinaryMarshaler),
[`encoding.BinaryUnmarshaler`](/pkg/encoding#BinaryUnmarshaler), [`encoding.TextMarshaler`](/pkg/encoding#TextMarshaler), [`encoding.TextUnmarshaler`](/pkg/encoding#TextUnmarshaler) interfaces.

#### [`database/sql`](/pkg/database/sql/)

Errors returned by [`driver.Valuer`](/pkg/driver#Valuer) implementations are now wrapped for
improved error handling during operations like [`DB.Query`](/pkg/database/sql#DB.Query), [`DB.Exec`](/pkg/database/sql#DB.Exec),
and [`DB.QueryRow`](/pkg/database/sql#DB.QueryRow).

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

The `debug/elf` package now defines [`PT_OPENBSD_NOBTCFI`](/pkg/debug/elf#PT_OPENBSD_NOBTCFI). This [`ProgType`](/pkg/debug/elf#ProgType) is
used to disable Branch Tracking Control Flow Integrity (BTCFI) enforcement
on OpenBSD binaries.

Now defines the symbol type constants [`STT_RELC`](/pkg/debug/elf#STT_RELC), [`STT_SRELC`](/pkg/debug/elf#STT_SRELC), and
[`STT_GNU_IFUNC`](/pkg/debug/elf#STT_GNU_IFUNC).

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

The new [`Encode`](/pkg/encoding/binary#Encode) and [`Decode`](/pkg/encoding/binary#Decode) functions are byte slice equivalents
to [`Read`](/pkg/encoding/binary#Read) and [`Write`](/pkg/encoding/binary#Write).
[`Append`](/pkg/encoding/binary#Append) allows marshaling multiple data into the same byte slice.

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

The new [`Preorder`](/pkg/go/ast#Preorder) function returns a convenient iterator over all the
nodes of a syntax tree.

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

<!-- see ../../../../2-language.md -->

The [`Func`](/pkg/go/types#Func) type, which represents a function or method symbol, now
has a [`Func.Signature`](/pkg/go/types#Func.Signature) method that returns the function's type, which
is always a `Signature`.

The [`Alias`](/pkg/go/types#Alias) type now has an [`Rhs`](/pkg/go/types#Rhs) method that returns the type on the
right-hand side of its declaration: given `type A = B`, the `Rhs` of A
is B. ([#66559](/issue/66559))

The methods [`Alias.Origin`](/pkg/go/types#Alias.Origin), [`Alias.SetTypeParams`](/pkg/go/types#Alias.SetTypeParams), [`Alias.TypeParams`](/pkg/go/types#Alias.TypeParams),
and [`Alias.TypeArgs`](/pkg/go/types#Alias.TypeArgs) have been added. They are needed for generic alias types.

<!-- CL 577715, CL 579076 -->
By default, go/types now produces [`Alias`](/pkg/go/types#Alias) type nodes for type aliases.
This behavior can be controlled by the `GODEBUG` `gotypesalias` flag.
Its default has changed from 0 in Go 1.22 to 1 in Go 1.23.

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

The [`Uint`](/pkg/math/rand/v2#Uint) function and [`Rand.Uint`](/pkg/math/rand/v2#Rand.Uint) method have been added.
They were inadvertently left out of Go 1.22.

The new [`ChaCha8.Read`](/pkg/math/rand/v2#ChaCha8.Read) method implements the [`io.Reader`](/pkg/io#Reader) interface.

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

The new type [`KeepAliveConfig`](/pkg/net#KeepAliveConfig) permits fine-tuning the keep-alive
options for TCP connections, via a new [`TCPConn.SetKeepAliveConfig`](/pkg/net#TCPConn.SetKeepAliveConfig)
method and new KeepAliveConfig fields for [`Dialer`](/pkg/net#Dialer) and [`ListenConfig`](/pkg/net#ListenConfig).

The [`DNSError`](/pkg/net#DNSError) type now wraps errors caused by timeouts or cancellation.
For example, `errors.Is(someDNSErr, context.DeadlineExceedeed)`
will now report whether a DNS error was caused by a timeout.

The new `GODEBUG` setting `netedns0=0` disables sending EDNS0
additional headers on DNS requests, as they reportedly break the DNS
server on some modems.

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

[`Cookie`](/pkg/net/http#Cookie) now preserves double quotes surrounding a cookie value.
The new [`Cookie.Quoted`](/pkg/net/http#Cookie.Quoted) field indicates whether the [`Cookie.Value`](/pkg/net/http#Cookie.Value)
was originally quoted.

The new [`Request.CookiesNamed`](/pkg/net/http#Request.CookiesNamed) method retrieves all cookies that match the given name.

The new [`Cookie.Partitioned`](/pkg/net/http#Cookie.Partitioned) field identifies cookies with the Partitioned attribute.

The patterns used by [`ServeMux`](/pkg/net/http#ServeMux) now allow one or more spaces or tabs after the method name.
Previously, only a single space was permitted.

The new [`ParseCookie`](/pkg/net/http#ParseCookie) function parses a Cookie header value and
returns all the cookies which were set in it. Since the same cookie
name can appear multiple times the returned Values can contain
more than one value for a given key.

The new [`ParseSetCookie`](/pkg/net/http#ParseSetCookie) function parses a Set-Cookie header value and
returns a cookie. It returns an error on syntax error.

[`ServeContent`](/pkg/net/http#ServeContent), [`ServeFile`](/pkg/net/http#ServeFile), and [`ServeFileFS`](/pkg/net/http#ServeFileFS) now remove
the `Cache-Control`, `Content-Encoding`, `Etag`, and `Last-Modified`
headers when serving an error. These headers usually apply to the
non-error content, but not to the text of errors.

Middleware which wraps a [`ResponseWriter`](/pkg/net/http#ResponseWriter) and applies on-the-fly
encoding, such as `Content-Encoding: gzip`, will not function after
this change.  The previous behavior of [`ServeContent`](/pkg/net/http#ServeContent), [`ServeFile`](/pkg/net/http#ServeFile),
and [`ServeFileFS`](/pkg/net/http#ServeFileFS) may be restored by setting
`GODEBUG=httpservecontentkeepheaders=1`.

Note that middleware which changes the size of the served content
(such as by compressing it) already does not function properly when
[`ServeContent`](/pkg/net/http#ServeContent) handles a Range request. On-the-fly compression
should use the `Transfer-Encoding` header instead of `Content-Encoding`.

For inbound requests, the new [`Request.Pattern`](/pkg/net/http#Request.Pattern) field contains the [`ServeMux`](/pkg/net/http#ServeMux)
pattern (if any) that matched the request. This field is not set when
`GODEBUG=httpmuxgo121=1` is set.

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

The new [`NewRequestWithContext`](/pkg/net/http/httptest#NewRequestWithContext) method creates an incoming request with
a [`context.Context`](/pkg/context#Context).

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

In Go 1.22 and earlier, using
[`reflect.DeepEqual`](/pkg/reflect#DeepEqual) to compare an
[`Addr`](/pkg/net/netip#Addr) holding an IPv4 address to one holding
the IPv4-mapped IPv6 form of that address incorrectly returned true,
even though the `Addr` values were different when comparing with `==` or
[`Addr.Compare`](/pkg/net/netip#Addr.Compare).
This bug is now fixed and all three approaches now report the same
result.

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

The [`Stat`](/pkg/os#Stat) function now sets the [`ModeSocket`](/pkg/os#ModeSocket) bit for
files that are Unix sockets on Windows. These files are identified
by having a reparse tag set to `IO_REPARSE_TAG_AF_UNIX`.

On Windows, the mode bits reported by [`Lstat`](/pkg/os#Lstat) and [`Stat`](/pkg/os#Stat) for
reparse points changed. Mount points no longer have [`ModeSymlink`](/pkg/os#ModeSymlink) set,
and reparse points that are not symlinks, Unix sockets, or dedup files
now always have [`ModeIrregular`](/pkg/os#ModeIrregular) set.
This behavior is controlled by the `winsymlink` setting.
For Go 1.23, it defaults to `winsymlink=1`.
Previous versions default to `winsymlink=0`.

The [`CopyFS`](/pkg/os#CopyFS) function copies an [`io/fs.FS`](/pkg/io/fs#FS) into the local filesystem.

On Windows, [`Readlink`](/pkg/os#Readlink) no longer tries to normalize volumes
to drive letters, which was not always even possible.
This behavior is controlled by the `winreadlinkvolume` setting.
For Go 1.23, it defaults to `winreadlinkvolume=1`.
Previous versions default to `winreadlinkvolume=0`.

<!-- go.dev/issue/62654, CL 570036, CL 570681 -->
On Linux with pidfd support (generally Linux v5.4+),
[`Process`](/pkg/os#Process)-related functions and methods use pidfd (rather
than PID) internally, eliminating potential mistargeting when a PID is reused
by the OS. Pidfd support is fully transparent to a user, except for additional
process file descriptors that a process may have.

#### [`path/filepath`](/pkg/path/filepath/)

The new [`Localize`](/pkg/path/filepath#Localize) function safely converts a slash-separated
path into an operating system path.

On Windows, [`EvalSymlinks`](/pkg/path/filepath#EvalSymlinks) no longer evaluates mount points,
which was a source of many inconsistencies and bugs.
This behavior is controlled by the `winsymlink` setting.
For Go 1.23, it defaults to `winsymlink=1`.
Previous versions default to `winsymlink=0`.

On Windows, [`EvalSymlinks`](/pkg/path/filepath#EvalSymlinks) no longer tries to normalize
volumes to drive letters, which was not always even possible.
This behavior is controlled by the `winreadlinkvolume` setting.
For Go 1.23, it defaults to `winreadlinkvolume=1`.
Previous versions default to `winreadlinkvolume=0`.

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

The new methods synonymous with the methods of the same name
in [`Value`](/pkg/reflect#Value) are added to [`Type`](/pkg/reflect#Type):
1. [`Type.OverflowComplex`](/pkg/reflect#Type.OverflowComplex)
2. [`Type.OverflowFloat`](/pkg/reflect#Type.OverflowFloat)
3. [`Type.OverflowInt`](/pkg/reflect#Type.OverflowInt)
4. [`Type.OverflowUint`](/pkg/reflect#Type.OverflowUint)

The new [`SliceAt`](/pkg/reflect#SliceAt) function is analogous to [`NewAt`](/pkg/reflect#NewAt), but for slices.

The [`Value.Pointer`](/pkg/reflect#Value.Pointer) and [`Value.UnsafePointer`](/pkg/reflect#Value.UnsafePointer) methods now support values of kind [`String`](/pkg/reflect#String).

The new methods [`Value.Seq`](/pkg/reflect#Value.Seq) and [`Value.Seq2`](/pkg/reflect#Value.Seq2) return sequences that iterate over the value
as though it were used in a for/range loop.
The new methods [`Type.CanSeq`](/pkg/reflect#Type.CanSeq) and [`Type.CanSeq2`](/pkg/reflect#Type.CanSeq2) report whether calling
[`Value.Seq`](/pkg/reflect#Value.Seq) and [`Value.Seq2`](/pkg/reflect#Value.Seq2), respectively, will succeed without panicking.

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

The [`SetCrashOutput`](/pkg/runtime/debug#SetCrashOutput) function allows the user to specify an alternate
file to which the runtime should write its fatal crash report.
It may be used to construct an automated reporting mechanism for all
unexpected crashes, not just those in goroutines that explicitly use
`recover`.

<!-- pacify TestCheckAPIFragments -->

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

The maximum stack depth for `alloc`, `mutex`, `block`, `threadcreate` and `goroutine`
profiles has been raised from 32 to 128 frames.

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

<!-- go.dev/issue/65319 -->
The runtime now explicitly flushes trace data when a program crashes due to an
uncaught panic. This means that more complete trace data will be available in a
trace if the program crashes while tracing is active.

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

<!-- see ../../3-iter.md -->

<!-- see ../../3-iter.md -->

The [`Repeat`](/pkg/slices#Repeat) function returns a new slice that repeats the
provided slice the given number of times.

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

The [`Map.Clear`](/pkg/sync#Map.Clear) method deletes all the entries, resulting in
an empty [`Map`](/pkg/sync#Map). It is analogous to `clear`.

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

<!-- Issue #61395 -->
The new [`And`](/pkg/sync/atomic#And) and [`Or`](/pkg/sync/atomic#Or) operators apply a bitwise `AND` or `OR` to
the given input, returning the old value.

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

The syscall package now defines [`WSAENOPROTOOPT`](/pkg/syscall#WSAENOPROTOOPT) on Windows.

The [`GetsockoptInt`](/pkg/syscall#GetsockoptInt) function is now supported on Windows.

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

[`TestFS`](/pkg/testing/fstest#TestFS) now returns a structured error that can be unwrapped
(via method `Unwrap() []error`). This allows inspecting errors
using [`errors.Is`](/pkg/errors#Is) or [`errors.As`](/pkg/errors#As).

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

Templates now support the new "else with" action, which reduces template complexity in some use cases.

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

[`Parse`](/pkg/time#Parse) and [`ParseInLocation`](/pkg/time#ParseInLocation) now return an error if the time zone
offset is out of range.

On Windows, [`Timer`](/pkg/time#Timer), [`Ticker`](/pkg/time#Ticker), and functions that put the goroutine to sleep,
such as [`Sleep`](/pkg/time#Sleep), got their time resolution improved to 0.5ms instead of 15.6ms.

#### [`unicode/utf16`](/pkg/unicode/utf16/)

The [`RuneLen`](/pkg/unicode/utf16#RuneLen) function returns the number of 16-bit words in
the UTF-16 encoding of the rune. It returns -1 if the rune
is not a valid value to encode in UTF-16.

## Ports {#ports}

### Darwin {#darwin}

<!-- go.dev/issue/64207 -->
As [announced](go1.22#darwin) in the Go 1.22 release notes,
Go 1.23 requires macOS 11 Big Sur or later;
support for previous versions has been discontinued.

### Linux {#linux}

<!-- go.dev/issue/67001 -->
Go 1.23 is the last release that requires Linux kernel version 2.6.32 or later. Go 1.24 will require Linux kernel version 3.2 or later.

### OpenBSD {#openbsd}

<!-- go.dev/issue/55999, CL 518629, CL 518630 -->
Go 1.23 adds experimental support for OpenBSD on 64-bit RISC-V (`GOOS=openbsd`, `GOARCH=riscv64`).

### ARM64 {#arm64}

<!-- go.dev/issue/60905, CL 559555 -->
Go 1.23 introduces a new `GOARM64` environment variable, which specifies the minimum target version of the ARM64 architecture at compile time. Allowed values are `v8.{0-9}` and `v9.{0-5}`. This may be followed by an option specifying extensions implemented by target hardware. Valid options are `,lse` and `,crypto`.

The `GOARM64` environment variable defaults to `v8.0`.

### RISC-V {#riscv}

<!-- go.dev/issue/61476, CL 541135 -->
Go 1.23 introduces a new `GORISCV64` environment variable, which selects the [RISC-V user-mode application profile](https://github.com/riscv/riscv-profiles/blob/main/src/profiles.adoc) for which to compile. Allowed values are `rva20u64` and `rva22u64`.

The `GORISCV64` environment variable defaults to `rva20u64`.

### Wasm {#wasm}

<!-- go.dev/issue/63718 -->
The `go_wasip1_wasm_exec` script in `GOROOT/misc/wasm` has dropped support
for versions of `wasmtime` < 14.0.0.

<!-- These items need to be completed and moved to an appropriate location in the release notes. -->

<!-- These items need to be reviewed, and mentioned in the Go 1.23 release notes if applicable.

None right now; more may come up later on.
-->

<!-- Maybe should be documented? Maybe shouldn't? Someone familiar with the change needs to determine.

CL 359594 ("x/website/_content/ref/mod: document dotless module paths") - resolved go.dev/issue/32819 ("cmd/go: document that module names without dots are reserved") and also mentioned accepted proposal go.dev/issue/37641
CL 555075 ("x/tools/go/ssa: support range-over-func") - x/tools CL implements range-over-func support in x/tools/go/ssa for accepted proposal https://go.dev/issue/66601; this particular proposal and change doesn't seem to need a dedicated mention in Go 1.23 release notes but someone more familiar should take another look
-->

<!-- Items that don't need to be mentioned in Go 1.23 release notes but are picked up by relnote todo.

CL 458895 - an x/playground fix that mentioned an accepted cmd/go proposal go.dev/issue/40728 in Go 1.16 milestone...
CL 582097 - an x/build CL working on relnote itself; it doesn't need a release note
CL 561935 - crypto CL that used purego tag and mentioned accepted-but-not-implemented proposal https://go.dev/issue/23172 to document purego tag; doesn't need a release note
CL 568340 - fixed a spurious race in time.Ticker.Reset (added via accepted proposal https://go.dev/issue/33184), doesn't seem to need a release note
CL 562619 - x/website CL documented minimum bootstrap version on go.dev, mentioning accepted proposals go.dev/issue/54265 and go.dev/issue/44505; doesn't need a release note
CL 557055 - x/tools CL implemented accepted proposal https://go.dev/issue/46941 for x/tools/go/ssa
CL 564275 - an x/tools CL that updates test data in preparation for accepted proposal https://go.dev/issue/51473; said proposal isn't implemented for Go 1.23 and so it doesn't need a release note
CL 572535 - used "unix" build tag in more places, mentioned accepted proposal https://go.dev/issue/51572; doesn't need a release note
CL 555255 - an x/tools CL implements accepted proposal https://go.dev/issue/53367 for x/tools/go/cfg
CL 585216 - an x/build CL mentions accepted proposal https://go.dev/issue/56001 because it fixed a bug causing downloads not to be produced for that new-to-Go-1.22 port; this isn't relevant to Go 1.23 release notes
CL 481062 - added examples for accepted proposal https://go.dev/issue/56102; doesn't need a release note
CL 497195 - an x/net CL adds one of 4 fields for accepted proposal https://go.dev/issue/57893 in x/net/http2; seemingly not related to net/http and so doesn't need a Go 1.23 release note
CL 463097, CL 568198 - x/net CLs that implemented accepted proposal https://go.dev/issue/57953 for x/net/websocket; no need for rel note
many x/net CLs - work on accepted proposal https://go.dev/issue/58547 to add a QUIC implementation to x/net/quic
CL 514775 - implements a performance optimization for accepted proposal https://go.dev/issue/59488
CL 484995 - x/sys CL implements accepted proposal https://go.dev/issue/59537 to add x/sys/unix API
CL 555597 - optimizes TypeFor (added in accepted proposal https://go.dev/issue/60088) for non-interface types; doesn't seem to need a release note
a few x/tools CLs deprecated and deleted the experimental golang.org/x/tools/cmd/getgo tool per accepted proposal https://go.dev/issue/60951; an unreleased change and not something that's in scope of Go 1.23 release notes
many x/vuln CLs to implement accepted proposal https://go.dev/issue/61347 ("x/vuln: convert govulncheck output to sarif format") in govulncheck
CL 516355 - x/crypto CL that implemented accepted proposal https://go.dev/issue/61447 for x/crypto/ssh; doesn't need a Go 1.23 release note
CL 559799 - a Go 1.22 release note edit CL mentioned a Go 1.22 accepted proposal https://go.dev/issue/62039, a little after Go 1.23 development began
CL 581555 - an x/tools CL mentioned accepted proposal https://go.dev/issue/62292 for x/tools/go/aalysis; doesn't need a Go 1.23 release note
CL 578355 - mentioned accepted proposal https://go.dev/issue/63131 to add GOARCH=wasm32, but that proposal hasn't been implemented in Go 1.23 so it doesn't need a release note
CL 543335 - x/exp CL that backported a change to behavior in slices package (accepted proposal https://go.dev/issue/63393) to x/exp/slices; doesn't need a Go 1.23 release note
CL 556820 - x/tools CL implemented accepted proposal https://go.dev/issue/64548 for x/tools/go/analysis
CL 557056 - x/tools CL implemented accepted proposal https://go.dev/issue/64608 for x/tools/go/packages
CL 558695 - x/crypto CL worked on accepted proposal https://go.dev/issue/64962 for x/crypto/ssh
CL 572016 - x/tools CL implemented accepted proposal https://go.dev/issue/65754 for x/tools/go/cfg
a few x/tools CLs tagged and deleted the golang.org/x/tools/cmd/guru command per accepted proposal https://go.dev/issue/65880; an unreleased change and not something that's in scope of Go 1.23 release notes
CL 580076 - seemingly internal cmd/go change to propagate module information for accepted proposal https://go.dev/issue/66315; doesn't seem to warrant a release note
CL 529816 - the 'tests' vet check was initially added to the 'go test' suite per accepted proposal https://go.dev/issue/44251, but the change was rolled back in CL 571695, with no roll forward as of 2024-05-23; nothing to document in Go 1.23 release notes for it at this time
CL 564035 - changed encoding/xml, but the change was too disrptive and rolled back in CL 570175, reopening tracking issue go.dev/issue/65691; nothing to document in Go 1.23 release notes
CL 587855 - a demonstration of benefit of accepted proposal https://go.dev/issue/60529; actual change isn't happening in Go 1.23 so doesn't need a release note
CL 526875 - x/crypto CL implemented accepted proposal https://go.dev/issue/62518 for x/crypto/ssh
-->