diff --git a/internal/strs/strings_unsafe.go b/internal/strs/strings_unsafe_go120.go
similarity index 96%
rename from internal/strs/strings_unsafe.go
rename to internal/strs/strings_unsafe_go120.go
index 61a84d341..a008acd09 100644
--- a/internal/strs/strings_unsafe.go
+++ b/internal/strs/strings_unsafe_go120.go
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build !purego && !appengine
-// +build !purego,!appengine
+//go:build !purego && !appengine && !go1.21
+// +build !purego,!appengine,!go1.21
 
 package strs
 
diff --git a/internal/strs/strings_unsafe_go121.go b/internal/strs/strings_unsafe_go121.go
new file mode 100644
index 000000000..60166f2ba
--- /dev/null
+++ b/internal/strs/strings_unsafe_go121.go
@@ -0,0 +1,74 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !purego && !appengine && go1.21
+// +build !purego,!appengine,go1.21
+
+package strs
+
+import (
+	"unsafe"
+
+	"google.golang.org/protobuf/reflect/protoreflect"
+)
+
+// UnsafeString returns an unsafe string reference of b.
+// The caller must treat the input slice as immutable.
+//
+// WARNING: Use carefully. The returned result must not leak to the end user
+// unless the input slice is provably immutable.
+func UnsafeString(b []byte) string {
+	return unsafe.String(unsafe.SliceData(b), len(b))
+}
+
+// UnsafeBytes returns an unsafe bytes slice reference of s.
+// The caller must treat returned slice as immutable.
+//
+// WARNING: Use carefully. The returned result must not leak to the end user.
+func UnsafeBytes(s string) []byte {
+	return unsafe.Slice(unsafe.StringData(s), len(s))
+}
+
+// Builder builds a set of strings with shared lifetime.
+// This differs from strings.Builder, which is for building a single string.
+type Builder struct {
+	buf []byte
+}
+
+// AppendFullName is equivalent to protoreflect.FullName.Append,
+// but optimized for large batches where each name has a shared lifetime.
+func (sb *Builder) AppendFullName(prefix protoreflect.FullName, name protoreflect.Name) protoreflect.FullName {
+	n := len(prefix) + len(".") + len(name)
+	if len(prefix) == 0 {
+		n -= len(".")
+	}
+	sb.grow(n)
+	sb.buf = append(sb.buf, prefix...)
+	sb.buf = append(sb.buf, '.')
+	sb.buf = append(sb.buf, name...)
+	return protoreflect.FullName(sb.last(n))
+}
+
+// MakeString is equivalent to string(b), but optimized for large batches
+// with a shared lifetime.
+func (sb *Builder) MakeString(b []byte) string {
+	sb.grow(len(b))
+	sb.buf = append(sb.buf, b...)
+	return sb.last(len(b))
+}
+
+func (sb *Builder) grow(n int) {
+	if cap(sb.buf)-len(sb.buf) >= n {
+		return
+	}
+
+	// Unlike strings.Builder, we do not need to copy over the contents
+	// of the old buffer since our builder provides no API for
+	// retrieving previously created strings.
+	sb.buf = make([]byte, 0, 2*(cap(sb.buf)+n))
+}
+
+func (sb *Builder) last(n int) string {
+	return UnsafeString(sb.buf[len(sb.buf)-n:])
+}