diff --git a/internal/cutil/aliases.go b/internal/cutil/aliases.go
index 309c19dab..70a786ff3 100644
--- a/internal/cutil/aliases.go
+++ b/internal/cutil/aliases.go
@@ -21,8 +21,14 @@ const (
 
 	// SizeTSize is the size of C.size_t
 	SizeTSize = C.sizeof_size_t
+
+	// IntSize is the size of C.int
+	IntSize = C.sizeof_int
 )
 
+// Compile-time assertion ensuring that Go's `int` is at least as large as C's.
+const _ = unsafe.Sizeof(int(0)) - unsafe.Sizeof(C.int(0))
+
 // SizeT wraps size_t from C.
 type SizeT C.size_t
 
diff --git a/rados/write_op_preview.go b/rados/write_op_preview.go
new file mode 100644
index 000000000..4c7bae3c2
--- /dev/null
+++ b/rados/write_op_preview.go
@@ -0,0 +1,65 @@
+//go:build ceph_preview
+// +build ceph_preview
+
+package rados
+
+// #cgo LDFLAGS: -lrados
+// #include <rados/librados.h>
+// #include <stdlib.h>
+//
+import "C"
+
+import (
+	"unsafe"
+
+	"github.com/ceph/go-ceph/internal/cutil"
+)
+
+// WriteOpCmpExtStep holds result of the CmpExt write operation.
+// Result is valid only after Operate() was called.
+type WriteOpCmpExtStep struct {
+	// C returned data:
+	prval *C.int
+
+	// Result of the CmpExt write operation.
+	Result int
+}
+
+func (s *WriteOpCmpExtStep) update() error {
+	s.Result = (int)(*s.prval)
+	return nil
+}
+
+func (s *WriteOpCmpExtStep) free() {
+	C.free(unsafe.Pointer(s.prval))
+	s.prval = nil
+}
+
+func newWriteOpCmpExtStep() *WriteOpCmpExtStep {
+	return &WriteOpCmpExtStep{
+		prval: (*C.int)(C.malloc(cutil.IntSize)),
+	}
+}
+
+// CmpExt ensures that given object range (extent) satisfies comparison.
+//  PREVIEW
+//
+// Implements:
+//  void rados_write_op_cmpext(rados_write_op_t write_op,
+//                             const char * cmp_buf,
+//                             size_t cmp_len,
+//                             uint64_t off,
+//                             int * prval);
+func (w *WriteOp) CmpExt(b []byte, offset uint64) *WriteOpCmpExtStep {
+	oe := newWriteStep(b, 0, offset)
+	cmpExtStep := newWriteOpCmpExtStep()
+	w.steps = append(w.steps, oe, cmpExtStep)
+	C.rados_write_op_cmpext(
+		w.op,
+		oe.cBuffer,
+		oe.cDataLen,
+		oe.cOffset,
+		cmpExtStep.prval)
+
+	return cmpExtStep
+}
diff --git a/rados/write_op_preview_test.go b/rados/write_op_preview_test.go
new file mode 100644
index 000000000..b6319db2e
--- /dev/null
+++ b/rados/write_op_preview_test.go
@@ -0,0 +1,40 @@
+//go:build ceph_preview
+// +build ceph_preview
+
+package rados
+
+import (
+	"github.com/stretchr/testify/assert"
+)
+
+func (suite *RadosTestSuite) TestWriteOpCmpExt() {
+	suite.SetupConnection()
+	ta := assert.New(suite.T())
+
+	oid := "TestWriteOpCmpExt"
+	data := []byte("compare this")
+
+	// Create an object and populate it with data.
+	op1 := CreateWriteOp()
+	defer op1.Release()
+	op1.Create(CreateIdempotent)
+	op1.WriteFull([]byte(data))
+	err := op1.Operate(suite.ioctx, oid, OperationNoFlag)
+	ta.NoError(err)
+
+	// Compare contents of the object. Should succeed.
+	op2 := CreateWriteOp()
+	defer op2.Release()
+	cmpExtRes1 := op2.CmpExt(data, 0)
+	err = op2.Operate(suite.ioctx, oid, OperationNoFlag)
+	ta.NoError(err)
+	ta.Equal(cmpExtRes1.Result, int(0))
+
+	// Compare contents of the object. Should fail.
+	op3 := CreateWriteOp()
+	defer op3.Release()
+	cmpExtRes2 := op3.CmpExt([]byte("xxx"), 0)
+	err = op3.Operate(suite.ioctx, oid, OperationNoFlag)
+	ta.Error(err)
+	ta.NotEqual(cmpExtRes2.Result, int(0))
+}