diff --git a/packages/protons-runtime/src/codec.ts b/packages/protons-runtime/src/codec.ts
index ab9a050..049893d 100644
--- a/packages/protons-runtime/src/codec.ts
+++ b/packages/protons-runtime/src/codec.ts
@@ -22,20 +22,32 @@ export interface EncodingLengthFunction<T> {
   (value: T): number
 }
 
+export interface DefaultValueFunction<T> {
+  (): T
+}
+
+export interface IsDefaultValueFunction<T> {
+  (value: T): boolean
+}
+
 export interface Codec<T> {
   name: string
   type: CODEC_TYPES
   encode: EncodeFunction<T>
   decode: DecodeFunction<T>
   encodingLength: EncodingLengthFunction<T>
+  defaultValue: DefaultValueFunction<T>
+  isDefaultValue: IsDefaultValueFunction<T>
 }
 
-export function createCodec <T> (name: string, type: CODEC_TYPES, encode: EncodeFunction<T>, decode: DecodeFunction<T>, encodingLength: EncodingLengthFunction<T>): Codec<T> {
+export function createCodec<T> (name: string, type: CODEC_TYPES, encode: EncodeFunction<T>, decode: DecodeFunction<T>, encodingLength: EncodingLengthFunction<T>, defaultValue: DefaultValueFunction<T>, isDefaultValue: IsDefaultValueFunction<T>): Codec<T> {
   return {
     name,
     type,
     encode,
     decode,
-    encodingLength
+    encodingLength,
+    defaultValue,
+    isDefaultValue
   }
 }
diff --git a/packages/protons-runtime/src/codecs/bool.ts b/packages/protons-runtime/src/codecs/bool.ts
index ec9932b..22bfe30 100644
--- a/packages/protons-runtime/src/codecs/bool.ts
+++ b/packages/protons-runtime/src/codecs/bool.ts
@@ -1,4 +1,4 @@
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<boolean> = function boolEncodingLength () {
@@ -13,4 +13,8 @@ const decode: DecodeFunction<boolean> = function boolDecode (buffer, offset) {
   return buffer.get(offset) > 0
 }
 
-export const bool = createCodec('bool', CODEC_TYPES.VARINT, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<boolean> = () => false
+
+const isDefaultValue: IsDefaultValueFunction<boolean> = (value: boolean) => !value
+
+export const bool = createCodec('bool', CODEC_TYPES.VARINT, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/bytes.ts b/packages/protons-runtime/src/codecs/bytes.ts
index d86ce3e..29bde31 100644
--- a/packages/protons-runtime/src/codecs/bytes.ts
+++ b/packages/protons-runtime/src/codecs/bytes.ts
@@ -1,8 +1,9 @@
 
 import { Uint8ArrayList } from 'uint8arraylist'
 import { unsigned } from '../utils/varint.js'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
+import { equals } from 'uint8arrays/equals'
 
 const encodingLength: EncodingLengthFunction<Uint8Array> = function bytesEncodingLength (val) {
   const len = val.byteLength
@@ -24,4 +25,8 @@ const decode: DecodeFunction<Uint8Array> = function bytesDecode (buf, offset) {
   return buf.subarray(offset, offset + byteLength)
 }
 
-export const bytes = createCodec('bytes', CODEC_TYPES.LENGTH_DELIMITED, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<Uint8Array> = () => new Uint8Array()
+
+const isDefaultValue: IsDefaultValueFunction<Uint8Array> = (value: Uint8Array) => equals(value, defaultValue())
+
+export const bytes = createCodec('bytes', CODEC_TYPES.LENGTH_DELIMITED, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/double.ts b/packages/protons-runtime/src/codecs/double.ts
index 9aabc63..35f5e96 100644
--- a/packages/protons-runtime/src/codecs/double.ts
+++ b/packages/protons-runtime/src/codecs/double.ts
@@ -1,5 +1,5 @@
 import { Uint8ArrayList } from 'uint8arraylist'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<number> = function doubleEncodingLength () {
@@ -17,4 +17,8 @@ const decode: DecodeFunction<number> = function doubleDecode (buf, offset) {
   return buf.getFloat64(offset, true)
 }
 
-export const double = createCodec('double', CODEC_TYPES.BIT64, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<number> = () => 0
+
+const isDefaultValue: IsDefaultValueFunction<number> = (value) => value === defaultValue()
+
+export const double = createCodec('double', CODEC_TYPES.BIT64, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/enum.ts b/packages/protons-runtime/src/codecs/enum.ts
index a8ef222..f2c2b72 100644
--- a/packages/protons-runtime/src/codecs/enum.ts
+++ b/packages/protons-runtime/src/codecs/enum.ts
@@ -1,6 +1,6 @@
 
 import { unsigned } from '../utils/varint.js'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction, Codec } from '../codec.js'
 
 export function enumeration <T> (v: any): Codec<T> {
@@ -42,6 +42,14 @@ export function enumeration <T> (v: any): Codec<T> {
     return v[strValue]
   }
 
+  const defaultValue: DefaultValueFunction<number | string> = function defaultValue () {
+    return Object.values(v)[0] as (string | number)
+  }
+
+  const isDefaultValue: IsDefaultValueFunction<number| string> = function isDefaultValue (val) {
+    return val === defaultValue()
+  }
+
   // @ts-expect-error yeah yeah
-  return createCodec('enum', CODEC_TYPES.VARINT, encode, decode, encodingLength)
+  return createCodec('enum', CODEC_TYPES.VARINT, encode, decode, encodingLength, defaultValue, isDefaultValue)
 }
diff --git a/packages/protons-runtime/src/codecs/fixed32.ts b/packages/protons-runtime/src/codecs/fixed32.ts
index 727e547..88888b3 100644
--- a/packages/protons-runtime/src/codecs/fixed32.ts
+++ b/packages/protons-runtime/src/codecs/fixed32.ts
@@ -1,5 +1,5 @@
 import { Uint8ArrayList } from 'uint8arraylist'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<number> = function fixed32EncodingLength () {
@@ -17,4 +17,8 @@ const decode: DecodeFunction<number> = function fixed32Decode (buf, offset) {
   return buf.getInt32(offset, true)
 }
 
-export const fixed32 = createCodec('fixed32', CODEC_TYPES.BIT32, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<number> = () => 0
+
+const isDefaultValue: IsDefaultValueFunction<number> = (val) => val === defaultValue()
+
+export const fixed32 = createCodec('fixed32', CODEC_TYPES.BIT32, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/fixed64.ts b/packages/protons-runtime/src/codecs/fixed64.ts
index cc3bc78..f86d13d 100644
--- a/packages/protons-runtime/src/codecs/fixed64.ts
+++ b/packages/protons-runtime/src/codecs/fixed64.ts
@@ -1,5 +1,5 @@
 import { Uint8ArrayList } from 'uint8arraylist'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<bigint> = function int64EncodingLength (val) {
@@ -17,4 +17,8 @@ const decode: DecodeFunction<bigint> = function int64Decode (buf, offset) {
   return buf.getBigInt64(offset, true)
 }
 
-export const fixed64 = createCodec('fixed64', CODEC_TYPES.BIT64, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<bigint> = () => 0n
+
+const isDefaultValue: IsDefaultValueFunction<bigint> = (val) => val === defaultValue()
+
+export const fixed64 = createCodec('fixed64', CODEC_TYPES.BIT64, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/float.ts b/packages/protons-runtime/src/codecs/float.ts
index 7ccdda2..77d3eee 100644
--- a/packages/protons-runtime/src/codecs/float.ts
+++ b/packages/protons-runtime/src/codecs/float.ts
@@ -1,5 +1,5 @@
 import { Uint8ArrayList } from 'uint8arraylist'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<number> = function floatEncodingLength () {
@@ -17,4 +17,8 @@ const decode: DecodeFunction<number> = function floatDecode (buf, offset) {
   return buf.getFloat32(offset, true)
 }
 
-export const float = createCodec('float', CODEC_TYPES.BIT32, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<number> = () => 0
+
+const isDefaultValue: IsDefaultValueFunction<number> = (val) => val === defaultValue()
+
+export const float = createCodec('float', CODEC_TYPES.BIT32, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/int32.ts b/packages/protons-runtime/src/codecs/int32.ts
index ef4c636..c494a2f 100644
--- a/packages/protons-runtime/src/codecs/int32.ts
+++ b/packages/protons-runtime/src/codecs/int32.ts
@@ -1,5 +1,5 @@
 import { signed } from '../utils/varint.js'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<number> = function int32EncodingLength (val) {
@@ -17,4 +17,8 @@ const decode: DecodeFunction<number> = function int32Decode (buf, offset) {
   return signed.decode(buf, offset)
 }
 
-export const int32 = createCodec('int32', CODEC_TYPES.VARINT, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<number> = () => 0
+
+const isDefaultValue: IsDefaultValueFunction<number> = (val) => val === defaultValue()
+
+export const int32 = createCodec('int32', CODEC_TYPES.VARINT, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/int64.ts b/packages/protons-runtime/src/codecs/int64.ts
index 47f571f..66f1c15 100644
--- a/packages/protons-runtime/src/codecs/int64.ts
+++ b/packages/protons-runtime/src/codecs/int64.ts
@@ -1,5 +1,5 @@
 import { signed } from '../utils/big-varint.js'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<bigint> = function int64EncodingLength (val) {
@@ -17,4 +17,8 @@ const decode: DecodeFunction<bigint> = function int64Decode (buf, offset) {
   return signed.decode(buf, offset) | 0n
 }
 
-export const int64 = createCodec('int64', CODEC_TYPES.VARINT, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<bigint> = () => 0n
+
+const isDefaultValue: IsDefaultValueFunction<bigint> = (val) => val === defaultValue()
+
+export const int64 = createCodec('int64', CODEC_TYPES.VARINT, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/message.ts b/packages/protons-runtime/src/codecs/message.ts
index 602a091..52ce46f 100644
--- a/packages/protons-runtime/src/codecs/message.ts
+++ b/packages/protons-runtime/src/codecs/message.ts
@@ -1,19 +1,28 @@
 import { unsigned } from '../utils/varint.js'
-import { createCodec, CODEC_TYPES } from '../codec.js'
-import type { DecodeFunction, EncodeFunction, EncodingLengthFunction, Codec } from '../codec.js'
+import type {
+  Codec,
+  DecodeFunction,
+  DefaultValueFunction,
+  EncodeFunction,
+  EncodingLengthFunction,
+  IsDefaultValueFunction
+} from '../codec.js'
+import { CODEC_TYPES, createCodec } from '../codec.js'
 import { Uint8ArrayList } from 'uint8arraylist'
-import type { FieldDefs, FieldDef } from '../index.js'
+import type { FieldDef, FieldDefs } from '../index.js'
 
 export interface Factory<A, T> {
   new (obj: A): T
 }
 
-export function message <T> (fieldDefs: FieldDefs): Codec<T> {
+export function message <T> (fieldDefs: FieldDefs, noDefaultOnWire: boolean): Codec<T> {
   const encodingLength: EncodingLengthFunction<T> = function messageEncodingLength (val: Record<string, any>) {
     let length = 0
 
     for (const fieldDef of Object.values(fieldDefs)) {
-      length += fieldDef.codec.encodingLength(val[fieldDef.name])
+      if (!noDefaultOnWire || !fieldDef.codec.isDefaultValue(val[fieldDef.name])) {
+        length += fieldDef.codec.encodingLength(val[fieldDef.name])
+      }
     }
 
     return unsigned.encodingLength(length) + length
@@ -31,6 +40,10 @@ export function message <T> (fieldDefs: FieldDefs): Codec<T> {
         throw new Error(`Non optional field "${fieldDef.name}" was ${value === null ? 'null' : 'undefined'}`)
       }
 
+      if (noDefaultOnWire && fieldDef.codec.isDefaultValue(value)) {
+        return
+      }
+
       const key = (fieldNumber << 3) | fieldDef.codec.type
       const prefix = new Uint8Array(unsigned.encodingLength(key))
       unsigned.encode(key, prefix)
@@ -116,15 +129,43 @@ export function message <T> (fieldDefs: FieldDefs): Codec<T> {
       offset += fieldLength
     }
 
-    // make sure repeated fields have an array if not set
     for (const fieldDef of Object.values(fieldDefs)) {
+      // make sure repeated fields have an array if not set
       if (fieldDef.repeats === true && fields[fieldDef.name] == null) {
         fields[fieldDef.name] = []
+      } else if (noDefaultOnWire && fields[fieldDef.name] == null) {
+        // apply default values if not set
+        fields[fieldDef.name] = fieldDef.codec.defaultValue()
       }
     }
 
     return fields
   }
 
-  return createCodec('message', CODEC_TYPES.LENGTH_DELIMITED, encode, decode, encodingLength)
+  // Need to initialized sub messages as default value.
+  const defaultValue: DefaultValueFunction<T> = function defaultValue () {
+    const defaultValue: any = {}
+
+    for (const fieldDef of Object.values(fieldDefs)) {
+      if (fieldDef.codec.type === CODEC_TYPES.LENGTH_DELIMITED) {
+        defaultValue[fieldDef.name] = fieldDef.codec.defaultValue()
+      }
+    }
+
+    return defaultValue
+  }
+
+  const isDefaultValue: IsDefaultValueFunction<T> = function isDefaultValue (val) {
+    for (const fieldDef of Object.values(fieldDefs)) {
+      // @ts-expect-error
+      const fieldValue = val[fieldDef.name]
+
+      if (!fieldDef.codec.isDefaultValue(fieldValue)) {
+        return false
+      }
+    }
+    return true
+  }
+
+  return createCodec('message', CODEC_TYPES.LENGTH_DELIMITED, encode, decode, encodingLength, defaultValue, isDefaultValue)
 }
diff --git a/packages/protons-runtime/src/codecs/sfixed32.ts b/packages/protons-runtime/src/codecs/sfixed32.ts
index 3958974..0608e45 100644
--- a/packages/protons-runtime/src/codecs/sfixed32.ts
+++ b/packages/protons-runtime/src/codecs/sfixed32.ts
@@ -1,5 +1,5 @@
 import { Uint8ArrayList } from 'uint8arraylist'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<number> = function sfixed32EncodingLength () {
@@ -17,4 +17,8 @@ const decode: DecodeFunction<number> = function sfixed32Decode (buf, offset) {
   return buf.getInt32(offset, true)
 }
 
-export const sfixed32 = createCodec('sfixed32', CODEC_TYPES.BIT32, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<number> = () => 0
+
+const isDefaultValue: IsDefaultValueFunction<number> = (val) => val === defaultValue()
+
+export const sfixed32 = createCodec('sfixed32', CODEC_TYPES.BIT32, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/sfixed64.ts b/packages/protons-runtime/src/codecs/sfixed64.ts
index 9e9a0ff..41524bb 100644
--- a/packages/protons-runtime/src/codecs/sfixed64.ts
+++ b/packages/protons-runtime/src/codecs/sfixed64.ts
@@ -1,5 +1,5 @@
 import { Uint8ArrayList } from 'uint8arraylist'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<bigint> = function sfixed64EncodingLength () {
@@ -17,4 +17,8 @@ const decode: DecodeFunction<bigint> = function sfixed64Decode (buf, offset) {
   return buf.getBigInt64(offset, true)
 }
 
-export const sfixed64 = createCodec('sfixed64', CODEC_TYPES.BIT64, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<bigint> = () => 0n
+
+const isDefaultValue: IsDefaultValueFunction<bigint> = (val) => val === defaultValue()
+
+export const sfixed64 = createCodec('sfixed64', CODEC_TYPES.BIT64, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/sint32.ts b/packages/protons-runtime/src/codecs/sint32.ts
index 88bbb4a..52ba72b 100644
--- a/packages/protons-runtime/src/codecs/sint32.ts
+++ b/packages/protons-runtime/src/codecs/sint32.ts
@@ -1,5 +1,5 @@
 import { zigzag } from '../utils/varint.js'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<number> = function sint32EncodingLength (val) {
@@ -18,4 +18,8 @@ const decode: DecodeFunction<number> = function svarintDecode (buf, offset) {
   return zigzag.decode(buf, offset)
 }
 
-export const sint32 = createCodec('sint32', CODEC_TYPES.VARINT, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<number> = () => 0
+
+const isDefaultValue: IsDefaultValueFunction<number> = (val) => val === defaultValue()
+
+export const sint32 = createCodec('sint32', CODEC_TYPES.VARINT, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/sint64.ts b/packages/protons-runtime/src/codecs/sint64.ts
index ca56ce8..568d197 100644
--- a/packages/protons-runtime/src/codecs/sint64.ts
+++ b/packages/protons-runtime/src/codecs/sint64.ts
@@ -1,5 +1,5 @@
 import { zigzag } from '../utils/big-varint.js'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<bigint> = function int64EncodingLength (val) {
@@ -17,4 +17,8 @@ const decode: DecodeFunction<bigint> = function int64Decode (buf, offset) {
   return zigzag.decode(buf, offset)
 }
 
-export const sint64 = createCodec('sint64', CODEC_TYPES.VARINT, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<bigint> = () => 0n
+
+const isDefaultValue: IsDefaultValueFunction<bigint> = (val) => val === defaultValue()
+
+export const sint64 = createCodec('sint64', CODEC_TYPES.VARINT, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/string.ts b/packages/protons-runtime/src/codecs/string.ts
index 04ebf11..c4cda06 100644
--- a/packages/protons-runtime/src/codecs/string.ts
+++ b/packages/protons-runtime/src/codecs/string.ts
@@ -1,7 +1,7 @@
 import { unsigned } from '../utils/varint.js'
 import { fromString as uint8ArrayFromString } from 'uint8arrays/from-string'
 import { toString as uint8ArrayToString } from 'uint8arrays/to-string'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 import { Uint8ArrayList } from 'uint8arraylist'
 
@@ -26,4 +26,8 @@ const decode: DecodeFunction<string> = function stringDecode (buf, offset) {
   return uint8ArrayToString(buf.subarray(offset, offset + strLen))
 }
 
-export const string = createCodec('string', CODEC_TYPES.LENGTH_DELIMITED, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<string> = () => ''
+
+const isDefaultValue: IsDefaultValueFunction<string> = (val) => val === defaultValue()
+
+export const string = createCodec('string', CODEC_TYPES.LENGTH_DELIMITED, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/uint32.ts b/packages/protons-runtime/src/codecs/uint32.ts
index 42d4153..6676d82 100644
--- a/packages/protons-runtime/src/codecs/uint32.ts
+++ b/packages/protons-runtime/src/codecs/uint32.ts
@@ -1,5 +1,5 @@
 import { unsigned } from '../utils/varint.js'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<number> = function uint32EncodingLength (val) {
@@ -22,4 +22,8 @@ const decode: DecodeFunction<number> = function uint32Decode (buf, offset) {
   // return value > 2147483647 ? value - 4294967296 : value
 }
 
-export const uint32 = createCodec('uint32', CODEC_TYPES.VARINT, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<number> = () => 0
+
+const isDefaultValue: IsDefaultValueFunction<number> = (val) => val === defaultValue()
+
+export const uint32 = createCodec('uint32', CODEC_TYPES.VARINT, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons-runtime/src/codecs/uint64.ts b/packages/protons-runtime/src/codecs/uint64.ts
index f8c2925..ee9b6fc 100644
--- a/packages/protons-runtime/src/codecs/uint64.ts
+++ b/packages/protons-runtime/src/codecs/uint64.ts
@@ -1,5 +1,5 @@
 import { unsigned } from '../utils/big-varint.js'
-import { createCodec, CODEC_TYPES } from '../codec.js'
+import { createCodec, CODEC_TYPES, DefaultValueFunction, IsDefaultValueFunction } from '../codec.js'
 import type { DecodeFunction, EncodeFunction, EncodingLengthFunction } from '../codec.js'
 
 const encodingLength: EncodingLengthFunction<bigint> = function uint64EncodingLength (val) {
@@ -18,4 +18,8 @@ const decode: DecodeFunction<bigint> = function uint64Decode (buf, offset) {
   return unsigned.decode(buf, offset)
 }
 
-export const uint64 = createCodec('uint64', CODEC_TYPES.VARINT, encode, decode, encodingLength)
+const defaultValue: DefaultValueFunction<bigint> = () => 0n
+
+const isDefaultValue: IsDefaultValueFunction<bigint> = (val) => val === defaultValue()
+
+export const uint64 = createCodec('uint64', CODEC_TYPES.VARINT, encode, decode, encodingLength, defaultValue, isDefaultValue)
diff --git a/packages/protons/bin/protons.ts b/packages/protons/bin/protons.ts
index a2ce94c..272e0c4 100644
--- a/packages/protons/bin/protons.ts
+++ b/packages/protons/bin/protons.ts
@@ -10,6 +10,7 @@ async function main () {
 
   Options
     --output, -o Path to a directory to write transpiled typescript files into
+    --no-default-on-wire Do not encode default values over the wire, decode absent fields as default values 
 
   Examples
     $ protons ./path/to/file.proto ./path/to/other/file.proto
@@ -19,6 +20,10 @@ async function main () {
       output: {
         type: 'string',
         alias: 'o'
+      },
+      defaultOnWire: {
+        type: 'boolean',
+        default: true
       }
     }
   })
diff --git a/packages/protons/src/index.ts b/packages/protons/src/index.ts
index 2b1cf98..cf2d3e4 100644
--- a/packages/protons/src/index.ts
+++ b/packages/protons/src/index.ts
@@ -125,7 +125,7 @@ function defineFields (fields: Record<string, FieldDef>, messageDef: MessageDef,
   })
 }
 
-function compileMessage (messageDef: MessageDef, moduleDef: ModuleDef): string {
+function compileMessage (messageDef: MessageDef, moduleDef: ModuleDef, noDefaultOnWire: boolean): string {
   if (isEnumDef(messageDef)) {
     moduleDef.imports.add('enumeration')
 
@@ -158,7 +158,7 @@ export namespace ${messageDef.name} {
   if (messageDef.nested != null) {
     nested = '\n'
     nested += Object.values(messageDef.nested)
-      .map(def => compileMessage(def, moduleDef).trim())
+      .map(def => compileMessage(def, moduleDef, noDefaultOnWire).trim())
       .join('\n\n')
       .split('\n')
       .map(line => line.trim() === '' ? '' : `  ${line}`)
@@ -213,7 +213,7 @@ export interface ${messageDef.name} {
 
         return `${fieldDef.id}: { name: '${name}', codec: ${codec}${fieldDef.options?.proto3_optional === true ? ', optional: true' : ''}${fieldDef.rule === 'repeated' ? ', repeats: true' : ''} }`
     }).join(',\n      ')}
-    })
+    }, ${noDefaultOnWire ? 'true' : 'false'})
   }
 
   export const encode = (obj: ${messageDef.name}): Uint8ArrayList => {
@@ -242,7 +242,7 @@ interface ModuleDef {
   globals: Record<string, ClassDef>
 }
 
-function defineModule (def: ClassDef): ModuleDef {
+function defineModule (def: ClassDef, noDefaultOnWire: boolean): ModuleDef {
   const moduleDef: ModuleDef = {
     imports: new Set(),
     importedTypes: new Set(),
@@ -280,7 +280,7 @@ function defineModule (def: ClassDef): ModuleDef {
   for (const className of Object.keys(defs)) {
     const classDef = defs[className]
 
-    moduleDef.compiled.push(compileMessage(classDef, moduleDef))
+    moduleDef.compiled.push(compileMessage(classDef, moduleDef, noDefaultOnWire))
   }
 
   return moduleDef
@@ -288,6 +288,7 @@ function defineModule (def: ClassDef): ModuleDef {
 
 interface Flags {
   output?: string
+  defaultOnWire: boolean
 }
 
 export async function generate (source: string, flags: Flags) {
@@ -299,7 +300,7 @@ export async function generate (source: string, flags: Flags) {
   }
 
   const def = JSON.parse(json)
-  const moduleDef = defineModule(def)
+  const moduleDef = defineModule(def, !flags.defaultOnWire)
 
   let lines = [
     '/* eslint-disable import/export */',
diff --git a/packages/protons/test/fixtures/basic.ts b/packages/protons/test/fixtures/basic.ts
index 7491aed..5e3e801 100644
--- a/packages/protons/test/fixtures/basic.ts
+++ b/packages/protons/test/fixtures/basic.ts
@@ -15,7 +15,7 @@ export namespace Basic {
     return message<Basic>({
       1: { name: 'foo', codec: string },
       2: { name: 'num', codec: int32 }
-    })
+    }, false)
   }
 
   export const encode = (obj: Basic): Uint8ArrayList => {
diff --git a/packages/protons/test/fixtures/circuit.ts b/packages/protons/test/fixtures/circuit.ts
index ec47246..71149f9 100644
--- a/packages/protons/test/fixtures/circuit.ts
+++ b/packages/protons/test/fixtures/circuit.ts
@@ -87,7 +87,7 @@ export namespace CircuitRelay {
       return message<Peer>({
         1: { name: 'id', codec: bytes },
         2: { name: 'addrs', codec: bytes, repeats: true }
-      })
+      }, false)
     }
 
     export const encode = (obj: Peer): Uint8ArrayList => {
@@ -105,7 +105,7 @@ export namespace CircuitRelay {
       2: { name: 'srcPeer', codec: CircuitRelay.Peer.codec(), optional: true },
       3: { name: 'dstPeer', codec: CircuitRelay.Peer.codec(), optional: true },
       4: { name: 'code', codec: CircuitRelay.Status.codec(), optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: CircuitRelay): Uint8ArrayList => {
diff --git a/packages/protons/test/fixtures/daemon.ts b/packages/protons/test/fixtures/daemon.ts
index 3c0a958..8e7b636 100644
--- a/packages/protons/test/fixtures/daemon.ts
+++ b/packages/protons/test/fixtures/daemon.ts
@@ -61,7 +61,7 @@ export namespace Request {
       7: { name: 'disconnect', codec: DisconnectRequest.codec(), optional: true },
       8: { name: 'pubsub', codec: PSRequest.codec(), optional: true },
       9: { name: 'peerStore', codec: PeerstoreRequest.codec(), optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: Request): Uint8ArrayList => {
@@ -111,7 +111,7 @@ export namespace Response {
       6: { name: 'peers', codec: PeerInfo.codec(), repeats: true },
       7: { name: 'pubsub', codec: PSResponse.codec(), optional: true },
       8: { name: 'peerStore', codec: PeerstoreResponse.codec(), optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: Response): Uint8ArrayList => {
@@ -133,7 +133,7 @@ export namespace IdentifyResponse {
     return message<IdentifyResponse>({
       1: { name: 'id', codec: bytes },
       2: { name: 'addrs', codec: bytes, repeats: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: IdentifyResponse): Uint8ArrayList => {
@@ -157,7 +157,7 @@ export namespace ConnectRequest {
       1: { name: 'peer', codec: bytes },
       2: { name: 'addrs', codec: bytes, repeats: true },
       3: { name: 'timeout', codec: int64, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: ConnectRequest): Uint8ArrayList => {
@@ -181,7 +181,7 @@ export namespace StreamOpenRequest {
       1: { name: 'peer', codec: bytes },
       2: { name: 'proto', codec: string, repeats: true },
       3: { name: 'timeout', codec: int64, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: StreamOpenRequest): Uint8ArrayList => {
@@ -203,7 +203,7 @@ export namespace StreamHandlerRequest {
     return message<StreamHandlerRequest>({
       1: { name: 'addr', codec: bytes },
       2: { name: 'proto', codec: string, repeats: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: StreamHandlerRequest): Uint8ArrayList => {
@@ -223,7 +223,7 @@ export namespace ErrorResponse {
   export const codec = (): Codec<ErrorResponse> => {
     return message<ErrorResponse>({
       1: { name: 'msg', codec: string }
-    })
+    }, false)
   }
 
   export const encode = (obj: ErrorResponse): Uint8ArrayList => {
@@ -247,7 +247,7 @@ export namespace StreamInfo {
       1: { name: 'peer', codec: bytes },
       2: { name: 'addr', codec: bytes },
       3: { name: 'proto', codec: string }
-    })
+    }, false)
   }
 
   export const encode = (obj: StreamInfo): Uint8ArrayList => {
@@ -309,7 +309,7 @@ export namespace DHTRequest {
       5: { name: 'value', codec: bytes, optional: true },
       6: { name: 'count', codec: int32, optional: true },
       7: { name: 'timeout', codec: int64, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: DHTRequest): Uint8ArrayList => {
@@ -351,7 +351,7 @@ export namespace DHTResponse {
       1: { name: 'type', codec: DHTResponse.Type.codec() },
       2: { name: 'peer', codec: PeerInfo.codec(), optional: true },
       3: { name: 'value', codec: bytes, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: DHTResponse): Uint8ArrayList => {
@@ -373,7 +373,7 @@ export namespace PeerInfo {
     return message<PeerInfo>({
       1: { name: 'id', codec: bytes },
       2: { name: 'addrs', codec: bytes, repeats: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: PeerInfo): Uint8ArrayList => {
@@ -417,7 +417,7 @@ export namespace ConnManagerRequest {
       2: { name: 'peer', codec: bytes, optional: true },
       3: { name: 'tag', codec: string, optional: true },
       4: { name: 'weight', codec: int64, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: ConnManagerRequest): Uint8ArrayList => {
@@ -437,7 +437,7 @@ export namespace DisconnectRequest {
   export const codec = (): Codec<DisconnectRequest> => {
     return message<DisconnectRequest>({
       1: { name: 'peer', codec: bytes }
-    })
+    }, false)
   }
 
   export const encode = (obj: DisconnectRequest): Uint8ArrayList => {
@@ -481,7 +481,7 @@ export namespace PSRequest {
       1: { name: 'type', codec: PSRequest.Type.codec() },
       2: { name: 'topic', codec: string, optional: true },
       3: { name: 'data', codec: bytes, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: PSRequest): Uint8ArrayList => {
@@ -511,7 +511,7 @@ export namespace PSMessage {
       4: { name: 'topicIDs', codec: string, repeats: true },
       5: { name: 'signature', codec: bytes, optional: true },
       6: { name: 'key', codec: bytes, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: PSMessage): Uint8ArrayList => {
@@ -533,7 +533,7 @@ export namespace PSResponse {
     return message<PSResponse>({
       1: { name: 'topics', codec: string, repeats: true },
       2: { name: 'peerIDs', codec: bytes, repeats: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: PSResponse): Uint8ArrayList => {
@@ -573,7 +573,7 @@ export namespace PeerstoreRequest {
       1: { name: 'type', codec: PeerstoreRequest.Type.codec() },
       2: { name: 'id', codec: bytes, optional: true },
       3: { name: 'protos', codec: string, repeats: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: PeerstoreRequest): Uint8ArrayList => {
@@ -595,7 +595,7 @@ export namespace PeerstoreResponse {
     return message<PeerstoreResponse>({
       1: { name: 'peer', codec: PeerInfo.codec(), optional: true },
       2: { name: 'protos', codec: string, repeats: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: PeerstoreResponse): Uint8ArrayList => {
diff --git a/packages/protons/test/fixtures/dht.ts b/packages/protons/test/fixtures/dht.ts
index 125655e..cdf078b 100644
--- a/packages/protons/test/fixtures/dht.ts
+++ b/packages/protons/test/fixtures/dht.ts
@@ -21,7 +21,7 @@ export namespace Record {
       3: { name: 'author', codec: bytes, optional: true },
       4: { name: 'signature', codec: bytes, optional: true },
       5: { name: 'timeReceived', codec: string, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: Record): Uint8ArrayList => {
@@ -99,7 +99,7 @@ export namespace Message {
         1: { name: 'id', codec: bytes, optional: true },
         2: { name: 'addrs', codec: bytes, repeats: true },
         3: { name: 'connection', codec: Message.ConnectionType.codec(), optional: true }
-      })
+      }, false)
     }
 
     export const encode = (obj: Peer): Uint8ArrayList => {
@@ -119,7 +119,7 @@ export namespace Message {
       3: { name: 'record', codec: bytes, optional: true },
       8: { name: 'closerPeers', codec: Message.Peer.codec(), repeats: true },
       9: { name: 'providerPeers', codec: Message.Peer.codec(), repeats: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: Message): Uint8ArrayList => {
diff --git a/packages/protons/test/fixtures/noise.ts b/packages/protons/test/fixtures/noise.ts
index 1c75bc4..9a1d207 100644
--- a/packages/protons/test/fixtures/noise.ts
+++ b/packages/protons/test/fixtures/noise.ts
@@ -18,7 +18,7 @@ export namespace pb {
         1: { name: 'identityKey', codec: bytes },
         2: { name: 'identitySig', codec: bytes },
         3: { name: 'data', codec: bytes }
-      })
+      }, false)
     }
 
     export const encode = (obj: NoiseHandshakePayload): Uint8ArrayList => {
diff --git a/packages/protons/test/fixtures/peer.ts b/packages/protons/test/fixtures/peer.ts
index f089a4f..2f23f7e 100644
--- a/packages/protons/test/fixtures/peer.ts
+++ b/packages/protons/test/fixtures/peer.ts
@@ -21,7 +21,7 @@ export namespace Peer {
       3: { name: 'metadata', codec: Metadata.codec(), repeats: true },
       4: { name: 'pubKey', codec: bytes, optional: true },
       5: { name: 'peerRecordEnvelope', codec: bytes, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: Peer): Uint8ArrayList => {
@@ -43,7 +43,7 @@ export namespace Address {
     return message<Address>({
       1: { name: 'multiaddr', codec: bytes },
       2: { name: 'isCertified', codec: bool, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: Address): Uint8ArrayList => {
@@ -65,7 +65,7 @@ export namespace Metadata {
     return message<Metadata>({
       1: { name: 'key', codec: string },
       2: { name: 'value', codec: bytes }
-    })
+    }, false)
   }
 
   export const encode = (obj: Metadata): Uint8ArrayList => {
diff --git a/packages/protons/test/fixtures/test-no-default-on-wire.proto b/packages/protons/test/fixtures/test-no-default-on-wire.proto
new file mode 100644
index 0000000..fc11bbf
--- /dev/null
+++ b/packages/protons/test/fixtures/test-no-default-on-wire.proto
@@ -0,0 +1,31 @@
+syntax = "proto3";
+
+enum AnEnum {
+  HERP = 0;
+  DERP = 1;
+}
+
+message SubMessage {
+  string foo = 1;
+}
+
+message AllTheTypesNoDefaultOnWire {
+  optional bool field1 = 1;
+  optional int32 field2 = 2;
+  optional int64 field3 = 3;
+  optional uint32 field4 = 4;
+  optional uint64 field5 = 5;
+  optional sint32 field6 = 6;
+  optional sint64 field7 = 7;
+  optional double field8 = 8;
+  optional float field9 = 9;
+  optional string field10 = 10;
+  optional bytes field11 = 11;
+  optional AnEnum field12 = 12;
+  optional SubMessage field13 = 13;
+  repeated string field14 = 14;
+  optional fixed32 field15 = 15;
+  optional fixed64 field16 = 16;
+  optional sfixed32 field17 = 17;
+  optional sfixed64 field18 = 18;
+}
diff --git a/packages/protons/test/fixtures/test-no-default-on-wire.ts b/packages/protons/test/fixtures/test-no-default-on-wire.ts
new file mode 100644
index 0000000..793ace8
--- /dev/null
+++ b/packages/protons/test/fixtures/test-no-default-on-wire.ts
@@ -0,0 +1,95 @@
+/* eslint-disable import/export */
+/* eslint-disable @typescript-eslint/no-namespace */
+
+import { enumeration, encodeMessage, decodeMessage, message, string, bool, int32, int64, uint32, uint64, sint32, sint64, double, float, bytes, fixed32, fixed64, sfixed32, sfixed64 } from 'protons-runtime'
+import type { Codec } from 'protons-runtime'
+import type { Uint8ArrayList } from 'uint8arraylist'
+
+export enum AnEnum {
+  HERP = 'HERP',
+  DERP = 'DERP'
+}
+
+enum __AnEnumValues {
+  HERP = 0,
+  DERP = 1
+}
+
+export namespace AnEnum {
+  export const codec = () => {
+    return enumeration<typeof AnEnum>(__AnEnumValues)
+  }
+}
+export interface SubMessage {
+  foo: string
+}
+
+export namespace SubMessage {
+  export const codec = (): Codec<SubMessage> => {
+    return message<SubMessage>({
+      1: { name: 'foo', codec: string }
+    }, true)
+  }
+
+  export const encode = (obj: SubMessage): Uint8ArrayList => {
+    return encodeMessage(obj, SubMessage.codec())
+  }
+
+  export const decode = (buf: Uint8Array | Uint8ArrayList): SubMessage => {
+    return decodeMessage(buf, SubMessage.codec())
+  }
+}
+
+export interface AllTheTypesNoDefaultOnWire {
+  field1?: boolean
+  field2?: number
+  field3?: bigint
+  field4?: number
+  field5?: bigint
+  field6?: number
+  field7?: bigint
+  field8?: number
+  field9?: number
+  field10?: string
+  field11?: Uint8Array
+  field12?: AnEnum
+  field13?: SubMessage
+  field14: string[]
+  field15?: number
+  field16?: bigint
+  field17?: number
+  field18?: bigint
+}
+
+export namespace AllTheTypesNoDefaultOnWire {
+  export const codec = (): Codec<AllTheTypesNoDefaultOnWire> => {
+    return message<AllTheTypesNoDefaultOnWire>({
+      1: { name: 'field1', codec: bool, optional: true },
+      2: { name: 'field2', codec: int32, optional: true },
+      3: { name: 'field3', codec: int64, optional: true },
+      4: { name: 'field4', codec: uint32, optional: true },
+      5: { name: 'field5', codec: uint64, optional: true },
+      6: { name: 'field6', codec: sint32, optional: true },
+      7: { name: 'field7', codec: sint64, optional: true },
+      8: { name: 'field8', codec: double, optional: true },
+      9: { name: 'field9', codec: float, optional: true },
+      10: { name: 'field10', codec: string, optional: true },
+      11: { name: 'field11', codec: bytes, optional: true },
+      12: { name: 'field12', codec: AnEnum.codec(), optional: true },
+      13: { name: 'field13', codec: SubMessage.codec(), optional: true },
+      14: { name: 'field14', codec: string, repeats: true },
+      15: { name: 'field15', codec: fixed32, optional: true },
+      16: { name: 'field16', codec: fixed64, optional: true },
+      17: { name: 'field17', codec: sfixed32, optional: true },
+      18: { name: 'field18', codec: sfixed64, optional: true }
+    }, true)
+  }
+
+  export const encode = (obj: AllTheTypesNoDefaultOnWire): Uint8ArrayList => {
+    return encodeMessage(obj, AllTheTypesNoDefaultOnWire.codec())
+  }
+
+  export const decode = (buf: Uint8Array | Uint8ArrayList): AllTheTypesNoDefaultOnWire => {
+    return decodeMessage(buf, AllTheTypesNoDefaultOnWire.codec())
+  }
+}
diff --git a/packages/protons/test/fixtures/test.ts b/packages/protons/test/fixtures/test.ts
index 11e6b16..e66b593 100644
--- a/packages/protons/test/fixtures/test.ts
+++ b/packages/protons/test/fixtures/test.ts
@@ -28,7 +28,7 @@ export namespace SubMessage {
   export const codec = (): Codec<SubMessage> => {
     return message<SubMessage>({
       1: { name: 'foo', codec: string }
-    })
+    }, false)
   }
 
   export const encode = (obj: SubMessage): Uint8ArrayList => {
@@ -82,7 +82,7 @@ export namespace AllTheTypes {
       16: { name: 'field16', codec: fixed64, optional: true },
       17: { name: 'field17', codec: sfixed32, optional: true },
       18: { name: 'field18', codec: sfixed64, optional: true }
-    })
+    }, false)
   }
 
   export const encode = (obj: AllTheTypes): Uint8ArrayList => {