diff --git a/generate/gen.go b/generate/gen.go
index 5eee0586..77b15a62 100644
--- a/generate/gen.go
+++ b/generate/gen.go
@@ -172,11 +172,6 @@ func (s Struct) WriteAppend(l *LineWriter) {
 	l.Write("if isFlexible {")
 	defer l.Write("}")
 
-	if len(tags) == 0 {
-		l.Write("dst = append(dst, 0)")
-		return
-	}
-
 	var tagsCanDefault bool
 	for i := 0; i < len(tags); i++ {
 		f, exists := tags[i]
@@ -188,6 +183,8 @@ func (s Struct) WriteAppend(l *LineWriter) {
 		}
 	}
 
+	defer l.Write("dst = v.UnknownTags.AppendEach(dst)")
+
 	if tagsCanDefault {
 		l.Write("var toEncode []uint32")
 		for i := 0; i < len(tags); i++ {
@@ -199,7 +196,12 @@ func (s Struct) WriteAppend(l *LineWriter) {
 				if !has {
 					def = d.GetTypeDefault()
 				}
-				l.Write("if v.%s != %v {", f.FieldName, def)
+				switch f.Type.(type) {
+				case Struct:
+					l.Write("if !reflect.DeepEqual(v.%s, %v) {", f.FieldName, def)
+				default:
+					l.Write("if v.%s != %v {", f.FieldName, def)
+				}
 			}
 			l.Write("toEncode = append(toEncode, %d)", i)
 			if canDefault {
@@ -207,13 +209,13 @@ func (s Struct) WriteAppend(l *LineWriter) {
 			}
 		}
 
-		l.Write("dst = kbin.AppendUvarint(dst, uint32(len(toEncode)))")
+		l.Write("dst = kbin.AppendUvarint(dst, uint32(len(toEncode) + v.UnknownTags.Len()))")
 		l.Write("for _, tag := range toEncode {")
 		l.Write("switch tag {")
 		defer l.Write("}")
 		defer l.Write("}")
 	} else {
-		l.Write("dst = kbin.AppendUvarint(dst, %d)", len(tags))
+		l.Write("dst = kbin.AppendUvarint(dst, %d + uint32(v.UnknownTags.Len()))", len(tags))
 	}
 
 	for i := 0; i < len(tags); i++ {
@@ -492,7 +494,7 @@ func (s Struct) WriteDecode(l *LineWriter) {
 
 	l.Write("if isFlexible {")
 	if len(tags) == 0 {
-		l.Write("SkipTags(&b)")
+		l.Write("s.UnknownTags = ReadTags(&b)")
 		l.Write("}")
 		return
 	}
@@ -501,11 +503,11 @@ func (s Struct) WriteDecode(l *LineWriter) {
 	l.Write("for i := b.Uvarint(); i > 0; i-- {")
 	defer l.Write("}")
 
-	l.Write("switch b.Uvarint() {")
+	l.Write("switch key := b.Uvarint(); key {")
 	defer l.Write("}")
 
 	l.Write("default:")
-	l.Write("b.Span(int(b.Uvarint()))") // unknown tag
+	l.Write("s.UnknownTags.Set(key, b.Span(int(b.Uvarint())))")
 
 	for i := 0; i < len(tags); i++ {
 		f, exists := tags[i]
@@ -566,7 +568,7 @@ func (s Struct) WriteDefn(l *LineWriter) {
 	l.Write("type %s struct {", s.Name)
 	if s.TopLevel {
 		// Top level messages always have a Version field.
-		l.Write("\t// Version is the version of this message used with a Kafka broker.")
+		l.Write("// Version is the version of this message used with a Kafka broker.")
 		l.Write("Version int16")
 		l.Write("")
 	}
@@ -591,6 +593,16 @@ func (s Struct) WriteDefn(l *LineWriter) {
 			l.Write("") // blank between fields
 		}
 	}
+	if s.FlexibleAt >= 0 {
+		l.Write("")
+		l.Write("// UnknownTags are tags Kafka sent that we do not know the purpose of.")
+		if s.FlexibleAt == 0 {
+			l.Write("UnknownTags Tags")
+		} else {
+			l.Write("UnknownTags Tags // v%d+", s.FlexibleAt)
+		}
+		l.Write("")
+	}
 	l.Write("}")
 }
 
diff --git a/generate/main.go b/generate/main.go
index 27d2d15f..d89f2b66 100644
--- a/generate/main.go
+++ b/generate/main.go
@@ -391,6 +391,7 @@ func main() {
 	l.Write("package kmsg")
 	l.Write("import (")
 	l.Write(`"context"`)
+	l.Write(`"reflect"`)
 	l.Write("")
 	l.Write(`"github.com/twmb/franz-go/pkg/kbin"`)
 	l.Write(")")