diff --git a/packages/react-transport-dom-relay/src/ReactFlightDOMRelayClient.js b/packages/react-transport-dom-relay/src/ReactFlightDOMRelayClient.js
index 4355f1aaa5e8e..73efb45ab98c8 100644
--- a/packages/react-transport-dom-relay/src/ReactFlightDOMRelayClient.js
+++ b/packages/react-transport-dom-relay/src/ReactFlightDOMRelayClient.js
@@ -22,11 +22,12 @@ import {
 export {createResponse, close};
 
 export function resolveRow(response: Response, chunk: RowEncoding): void {
-  if (chunk.type === 'json') {
-    resolveModel(response, chunk.id, chunk.json);
-  } else if (chunk.type === 'module') {
-    resolveModule(response, chunk.id, chunk.json);
-  } else {
-    resolveError(response, chunk.id, chunk.json.message, chunk.json.stack);
+  if (chunk[0] === 'J') {
+    resolveModel(response, chunk[1], chunk[2]);
+  } else if (chunk[0] === 'M') {
+    resolveModule(response, chunk[1], chunk[2]);
+  } else if (chunk[0] === 'E') {
+    // $FlowFixMe: Flow doesn't support disjoint unions on tuples.
+    resolveError(response, chunk[1], chunk[2].message, chunk[2].stack);
   }
 }
diff --git a/packages/react-transport-dom-relay/src/ReactFlightDOMRelayProtocol.js b/packages/react-transport-dom-relay/src/ReactFlightDOMRelayProtocol.js
index efbf82ed25c1a..263161d53852d 100644
--- a/packages/react-transport-dom-relay/src/ReactFlightDOMRelayProtocol.js
+++ b/packages/react-transport-dom-relay/src/ReactFlightDOMRelayProtocol.js
@@ -18,22 +18,14 @@ export type JSONValue =
   | Array<JSONValue>;
 
 export type RowEncoding =
-  | {
-      type: 'json',
-      id: number,
-      json: JSONValue,
-    }
-  | {
-      type: 'module',
-      id: number,
-      json: ModuleMetaData,
-    }
-  | {
-      type: 'error',
-      id: number,
-      json: {
+  | ['J', number, JSONValue]
+  | ['M', number, ModuleMetaData]
+  | [
+      'E',
+      number,
+      {
         message: string,
         stack: string,
         ...
       },
-    };
+    ];
diff --git a/packages/react-transport-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js b/packages/react-transport-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js
index f995116ce30bc..d3fc134176a96 100644
--- a/packages/react-transport-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js
+++ b/packages/react-transport-dom-relay/src/ReactFlightDOMRelayServerHostConfig.js
@@ -53,14 +53,14 @@ export function processErrorChunk(
   message: string,
   stack: string,
 ): Chunk {
-  return {
-    type: 'error',
-    id: id,
-    json: {
+  return [
+    'E',
+    id,
+    {
       message,
       stack,
     },
-  };
+  ];
 }
 
 function convertModelToJSON(
@@ -99,11 +99,7 @@ export function processModelChunk(
   model: ReactModel,
 ): Chunk {
   const json = convertModelToJSON(request, {}, '', model);
-  return {
-    type: 'json',
-    id: id,
-    json: json,
-  };
+  return ['J', id, json];
 }
 
 export function processModuleChunk(
@@ -112,11 +108,7 @@ export function processModuleChunk(
   moduleMetaData: ModuleMetaData,
 ): Chunk {
   // The moduleMetaData is already a JSON serializable value.
-  return {
-    type: 'module',
-    id: id,
-    json: moduleMetaData,
-  };
+  return ['M', id, moduleMetaData];
 }
 
 export function scheduleWork(callback: () => void) {
diff --git a/packages/react-transport-native-relay/src/ReactFlightNativeRelayClient.js b/packages/react-transport-native-relay/src/ReactFlightNativeRelayClient.js
index f023b0dc15a8c..872411f97a790 100644
--- a/packages/react-transport-native-relay/src/ReactFlightNativeRelayClient.js
+++ b/packages/react-transport-native-relay/src/ReactFlightNativeRelayClient.js
@@ -22,11 +22,12 @@ import {
 export {createResponse, close};
 
 export function resolveRow(response: Response, chunk: RowEncoding): void {
-  if (chunk.type === 'json') {
-    resolveModel(response, chunk.id, chunk.json);
-  } else if (chunk.type === 'module') {
-    resolveModule(response, chunk.id, chunk.json);
-  } else {
-    resolveError(response, chunk.id, chunk.json.message, chunk.json.stack);
+  if (chunk[0] === 'J') {
+    resolveModel(response, chunk[1], chunk[2]);
+  } else if (chunk[0] === 'M') {
+    resolveModule(response, chunk[1], chunk[2]);
+  } else if (chunk[0] === 'E') {
+    // $FlowFixMe: Flow doesn't support disjoint unions on tuples.
+    resolveError(response, chunk[1], chunk[2].message, chunk[2].stack);
   }
 }
diff --git a/packages/react-transport-native-relay/src/ReactFlightNativeRelayProtocol.js b/packages/react-transport-native-relay/src/ReactFlightNativeRelayProtocol.js
index 9f59b3040d911..5689f8c0f974c 100644
--- a/packages/react-transport-native-relay/src/ReactFlightNativeRelayProtocol.js
+++ b/packages/react-transport-native-relay/src/ReactFlightNativeRelayProtocol.js
@@ -18,22 +18,14 @@ export type JSONValue =
   | Array<JSONValue>;
 
 export type RowEncoding =
-  | {
-      type: 'json',
-      id: number,
-      json: JSONValue,
-    }
-  | {
-      type: 'module',
-      id: number,
-      json: ModuleMetaData,
-    }
-  | {
-      type: 'error',
-      id: number,
-      json: {
+  | ['J', number, JSONValue]
+  | ['M', number, ModuleMetaData]
+  | [
+      'E',
+      number,
+      {
         message: string,
         stack: string,
         ...
       },
-    };
+    ];
diff --git a/packages/react-transport-native-relay/src/ReactFlightNativeRelayServerHostConfig.js b/packages/react-transport-native-relay/src/ReactFlightNativeRelayServerHostConfig.js
index b2a12efb4a0b0..bd28ee0337521 100644
--- a/packages/react-transport-native-relay/src/ReactFlightNativeRelayServerHostConfig.js
+++ b/packages/react-transport-native-relay/src/ReactFlightNativeRelayServerHostConfig.js
@@ -53,14 +53,14 @@ export function processErrorChunk(
   message: string,
   stack: string,
 ): Chunk {
-  return {
-    type: 'error',
-    id: id,
-    json: {
+  return [
+    'E',
+    id,
+    {
       message,
       stack,
     },
-  };
+  ];
 }
 
 function convertModelToJSON(
@@ -99,11 +99,7 @@ export function processModelChunk(
   model: ReactModel,
 ): Chunk {
   const json = convertModelToJSON(request, {}, '', model);
-  return {
-    type: 'json',
-    id: id,
-    json: json,
-  };
+  return ['J', id, json];
 }
 
 export function processModuleChunk(
@@ -112,11 +108,7 @@ export function processModuleChunk(
   moduleMetaData: ModuleMetaData,
 ): Chunk {
   // The moduleMetaData is already a JSON serializable value.
-  return {
-    type: 'module',
-    id: id,
-    json: moduleMetaData,
-  };
+  return ['M', id, moduleMetaData];
 }
 
 export function scheduleWork(callback: () => void) {