Next Release Notes Draft
DRAFT RELEASE NOTES — Introduction to Go 1.27
Go 1.27 is not yet released. These are work-in-progress release notes. Go 1.27 is expected to be released in August 2026.
Tools
Response file (@file) parsing is now supported for the compile, link, asm, cgo, cover, and pack tools.
The response file contains whitespace-separated arguments with support for single-quoted and double-quoted strings, escape sequences, and backslash-newline line continuation.
The format is compatible with GCC’s response file implementation to ensure interoperability with existing build systems.
Go command
go test now invokes the stdversion vet check by default.
This reports the use of standard library symbols that are too new
for the Go version in force in the referring file,
as determined by go directive in go.mod and build tags on the file.
The go command no longer has support for the bzr version control system.
It will no longer be able to directly fetch modules hosted on bzr servers.
Trace
go tool trace’s -http argument now restricts the listen address to localhost when passed only a port (e.g., -http=:6060).
This change makes go tool trace consistent with the behavior of go tool pprof’s -http flag.
To listen on all addresses, explicitly include the specified address (e.g., -http=0.0.0.0:6060).
Runtime
Tracebacks for modules with go directives configuring Go 1.27 or later will now
include runtime/pprof goroutine labels in
the header line. This behavior can be disabled with GODEBUG=tracebacklabels=0
(added in Go 1.26). This opt-out is expected to be
kept indefinitely in case goroutine labels acquire sensitive information that
shouldn’t be made available in tracebacks.
Compiler
The compiler now resolves a relative filename in a //line or /*line*/
directive against the directory of the file containing the directive,
matching go/scanner. Absolute filenames are unaffected.
See #70478.
Standard library
uuid
The new uuid package generates and parses UUIDs.
crypto/mldsa
The new crypto/mldsa package implements the post-quantum ML-DSA signature
scheme specified in FIPS 204.
crypto/x509 now supports ML-DSA private keys, public keys, and signatures.
crypto/tls now supports ML-DSA signatures in TLS 1.3, with the new
[MLDSA44], [MLDSA65], and [MLDSA87] [SignatureScheme] values.
Minor changes to the library
bytes
The new CutLast function slices a []byte
around the last occurrence of a separator.
It can replace and simplify some common uses of LastIndex.
crypto
The new MLDSAMu Hash value is meant to be used as a signaling mechanism for
External μ ML-DSA signing.
crypto/ecdsa
PrivateKey.Sign now checks that the length of the hash is correct, if opts is
not nil.
crypto/mldsa
crypto/tls
The new QUICConfig.ClientHelloInfoConn field specifies the net.Conn to use
for the ClientHelloInfo.Conn field during QUIC server handshakes.
The MLKEM1024 key exchange is now supported. It can be enabled by adding it to
Config.CurvePreferences.
Config.Rand is now deprecated.
For deterministic testing, use testing/cryptotest.SetGlobalRandom.
Post-quantum hybrid key exchanges can now be explicitly enabled in
Config.CurvePreferences even if the tlsmlkem=0 or tlssecpmlkem=0 GODEBUG
options are used. Those options were always meant to only apply to the default
set used when Config.CurvePreferences is nil.
crypto/x509
When parsing into pkix.Name fields, a wider range of
pkix.AttributeTypeAndValue.Value types is now supported, and unknown types are
parsed into asn1.RawValue.
The new Certificate.RawSignatureAlgorithm, CertificateRequest.RawSignatureAlgorithm,
and RevocationList.RawSignatureAlgorithm fields expose the DER-encoded
AlgorithmIdentifier of the signature algorithm, including when the
SignatureAlgorithm field is UnknownSignatureAlgorithm.
SystemCertPool now respects SSL_CERT_FILE and SSL_CERT_DIR on Windows and
Darwin. When these environment variables are set, roots are loaded from disk and
instead of using the platform certificate verification APIs, the native Go
verifier is used. This behavior can be disabled with
GODEBUG=x509sslcertoverrideplatform=0.
crypto/x509/pkix
RDNSequence.String (and therefore Name.String) now renders string-typed
attribute values as strings even when the attribute’s OID is unrecognized.
Previously such values were always hex-encoded in their DER form.
See #33093.
database/sql
The new ConvertAssign function gives database drivers access
to the type conversions performed by Rows.Scan.
database/sql/driver
Drivers may implement the new RowsColumnScanner interface
to scan directly into user-provided destinations.
go/constant
The new StringLen function returns the length of a string Value. For an Unknown value, the length is 0.
go/scanner
The scanner now allows retrieving the end position of a token via the new Scanner.End method.
go/token
File now has a String method.
go/types
The Hasher type is an implementation of maphash.Hasher for [Type]s
that respects the Identical equivalence relation, allowing Types
to be used in hash tables and similar data structures (see container/hash).
HasherIgnoreTags is the analogous hasher for IdenticalIgnoreTags.
hash/maphash
The Hasher interface type defines the contract between values of a
particular type and future hash-based data structures such as hash
tables and Bloom filters; see #70471.
math/big
Int now has method Int.Divide to compute quotient and remainder of two Int values.
It supports rounding modes Trunc, Floor, Round and Ceil.
math/rand/v2
add the generic method *Rand.N, matching the behavior of the top-level N function.
net
net: UnixConn read methods now return io.EOF directly instead of wrapping it in net.OpError when the underlying read returns EOF.
net/http
Transport and Server support TLS ALPN protocol negotiation on
user-provided net.Conn connections which implement a
ConnectionState() tls.ConnectionState method.
HTTP/2 server now accepts client priority signals, as defined in RFC 9218,
allowing it to prioritize serving HTTP/2 streams with higher priority. If the
old behavior is preferred, where streams are served in a round-robin manner
regardless of priority, Server.DisableClientPriority can be set to true.
HTTP/1 Response.Body now automatically drains any unread content upon being
closed, up to a conservative limit, to allow better connection reuse. For most
programs, this change should be a no-op, or result in a performance improvement.
In rare cases, programs that do not benefit from connection reuse might
experience performance degradation if they had been improperly allowing an
excessive amount of idle connections to linger; usually by setting
Transport.MaxIdleConns to 0 or using different [Client]s for different
requests, thereby bypassing Transport.MaxIdleConns limit. In these cases,
setting Transport.DisableKeepAlives to true will disable connection reuse.
However, such performance degradation usually indicates improper configuration
or usage of Transport or Client in the first place, and a deeper look would
likely be beneficial.
net/http/httptest
NewTestServer creates a Server configured to use an in-memory
fake network suitable for use with the testing/synctest package.
net/url
The new URL.Clone method creates a deep copy of a URL.
The new Values.Clone method creates a deep copy of Values.
strings
The new CutLast function slices a string
around the last occurrence of a separator.
It can replace and simplify some common uses of LastIndex.
testing/synctest
The new Sleep helper function combines time.Sleep and testing/synctest.Wait.
unicode
The unicode package and associated support throughout the system has been upgraded from Unicode 15 to Unicode 17. See the Unicode 16.0.0 and Unicode 17.0.0 release notes for information about the changes.
uuid
Ports
Darwin
As announced in the Go 1.26 release notes, Go 1.27 requires macOS 13 Ventura or later; support for previous versions has been discontinued.
Linux
On ppc64, the ABI has been migrated to ELFv2. This change has no effect for those building and running pure Go binaries.
On ppc64, external linking, cgo, and PIE binaries are now supported. Using these features requires an ELFv2 compatible runtime (libc, kernel, and all linked and loaded libraries).