diff --git a/codec/codec.go b/codec/codec.go
index 3de1899a..b850cf8f 100644
--- a/codec/codec.go
+++ b/codec/codec.go
@@ -1,5 +1,5 @@
 // Package codec is an interface for encoding messages
-package codec // import "go.unistack.org/micro/v3/codec"
+package codec
 
 import (
 	"errors"
@@ -13,8 +13,6 @@ var (
 )
 
 var (
-	// DefaultMaxMsgSize specifies how much data codec can handle
-	DefaultMaxMsgSize = 1024 * 1024 * 4 // 4Mb
 	// DefaultCodec is the global default codec
 	DefaultCodec = NewCodec()
 	// DefaultTagName specifies struct tag name to control codec Marshal/Unmarshal
@@ -28,21 +26,10 @@ type Codec interface {
 	String() string
 }
 
-// MarshalAppend calls codec.Marshal(v) and returns the data appended to buf.
-// If codec implements MarshalAppend, that is called instead.
-func MarshalAppend(buf []byte, c Codec, v interface{}, opts ...Option) ([]byte, error) {
-	if nc, ok := c.(interface {
-		MarshalAppend([]byte, interface{}, ...Option) ([]byte, error)
-	}); ok {
-		return nc.MarshalAppend(buf, v, opts...)
-	}
-
-	mbuf, err := c.Marshal(v, opts...)
-	if err != nil {
-		return nil, err
-	}
-
-	return append(buf, mbuf...), nil
+type CodecV2 interface {
+	Marshal(buf []byte, v interface{}, opts ...Option) ([]byte, error)
+	Unmarshal(buf []byte, v interface{}, opts ...Option) error
+	String() string
 }
 
 // RawMessage is a raw encoded JSON value.
diff --git a/codec/options.go b/codec/options.go
index afcfb1c5..a0ed6e54 100644
--- a/codec/options.go
+++ b/codec/options.go
@@ -23,15 +23,8 @@ type Options struct {
 	Context context.Context
 	// TagName specifies tag name in struct to control codec
 	TagName string
-	// MaxMsgSize specifies max messages size that reads by codec
-	MaxMsgSize int
-}
-
-// MaxMsgSize sets the max message size
-func MaxMsgSize(n int) Option {
-	return func(o *Options) {
-		o.MaxMsgSize = n
-	}
+	// Flatten specifies that struct must be analyzed for flatten tag
+	Flatten bool
 }
 
 // TagName sets the codec tag name in struct
@@ -65,12 +58,12 @@ func Meter(m meter.Meter) Option {
 // NewOptions returns new options
 func NewOptions(opts ...Option) Options {
 	options := Options{
-		Context:    context.Background(),
-		Logger:     logger.DefaultLogger,
-		Meter:      meter.DefaultMeter,
-		Tracer:     tracer.DefaultTracer,
-		MaxMsgSize: DefaultMaxMsgSize,
-		TagName:    DefaultTagName,
+		Context: context.Background(),
+		Logger:  logger.DefaultLogger,
+		Meter:   meter.DefaultMeter,
+		Tracer:  tracer.DefaultTracer,
+		TagName: DefaultTagName,
+		Flatten: false,
 	}
 
 	for _, o := range opts {