diff --git a/packages/remix-server-runtime/jsonify.ts b/packages/remix-server-runtime/jsonify.ts
index 80a6c2b5a..80e524ff5 100644
--- a/packages/remix-server-runtime/jsonify.ts
+++ b/packages/remix-server-runtime/jsonify.ts
@@ -21,6 +21,9 @@ export type Jsonify<T> =
   T extends Number ? number :
   T extends Boolean ? boolean :
 
+  // Promises JSON.stringify to an empty object
+  T extends Promise<unknown> ? EmptyObject :
+
   // Map & Set
   T extends Map<unknown, unknown> ? EmptyObject :
   T extends Set<unknown> ? EmptyObject :
@@ -119,6 +122,7 @@ type _tests = [
   Expect<Equal<Jsonify<String>, string>>,
   Expect<Equal<Jsonify<Number>, number>>,
   Expect<Equal<Jsonify<Boolean>, boolean>>,
+  Expect<Equal<Jsonify<Promise<string>>, EmptyObject>>,
 
   // Map & Set
   Expect<Equal<Jsonify<Map<unknown, unknown>>, EmptyObject>>,
@@ -251,7 +255,7 @@ type NeverToNull<T> = [T] extends [never] ? null : T;
 
 // adapted from https://github.com/sindresorhus/type-fest/blob/main/source/empty-object.d.ts
 declare const emptyObjectSymbol: unique symbol;
-type EmptyObject = { [emptyObjectSymbol]?: never };
+export type EmptyObject = { [emptyObjectSymbol]?: never };
 
 // adapted from https://github.com/type-challenges/type-challenges/blob/main/utils/index.d.ts
 type IsAny<T> = 0 extends 1 & T ? true : false;
diff --git a/packages/remix-server-runtime/routeModules.ts b/packages/remix-server-runtime/routeModules.ts
index f9bacaf54..807276a67 100644
--- a/packages/remix-server-runtime/routeModules.ts
+++ b/packages/remix-server-runtime/routeModules.ts
@@ -54,7 +54,7 @@ type ClientActionFunction = (
  * Arguments passed to a route `clientAction` function
  * @private Public API is exported from @remix-run/react
  */
-type ClientActionFunctionArgs = RRActionFunctionArgs<undefined> & {
+export type ClientActionFunctionArgs = RRActionFunctionArgs<undefined> & {
   serverAction: <T = AppData>() => Promise<SerializeFrom<T>>;
 };
 
@@ -87,7 +87,7 @@ type ClientLoaderFunction = ((
  * Arguments passed to a route `clientLoader` function
  * @private Public API is exported from @remix-run/react
  */
-type ClientLoaderFunctionArgs = RRLoaderFunctionArgs<undefined> & {
+export type ClientLoaderFunctionArgs = RRLoaderFunctionArgs<undefined> & {
   serverLoader: <T = AppData>() => Promise<SerializeFrom<T>>;
 };
 
diff --git a/packages/remix-server-runtime/serialize.ts b/packages/remix-server-runtime/serialize.ts
index 4a2a8a3a7..c3d4822f4 100644
--- a/packages/remix-server-runtime/serialize.ts
+++ b/packages/remix-server-runtime/serialize.ts
@@ -1,21 +1,60 @@
-import type { Jsonify } from "./jsonify";
+import type { EmptyObject, Jsonify } from "./jsonify";
 import type { TypedDeferredData, TypedResponse } from "./responses";
+import type {
+  ClientActionFunctionArgs,
+  ClientLoaderFunctionArgs,
+} from "./routeModules";
 import { expectType } from "./typecheck";
 import { type Expect, type Equal } from "./typecheck";
 
 // prettier-ignore
 /**
- * Infer JSON serialized data type returned by a loader or action.
+ * Infer JSON serialized data type returned by a loader or action, while
+ * avoiding deserialization if the input type if it's a clientLoader or
+ * clientAction that returns a non-Response
  *
  * For example:
  * `type LoaderData = SerializeFrom<typeof loader>`
  */
 export type SerializeFrom<T> =
-  T extends (...args: any[]) => infer Output ? Serialize<Awaited<Output>> :
+  T extends (...args: any[]) => infer Output ?
+    Parameters<T> extends [ClientLoaderFunctionArgs | ClientActionFunctionArgs] ?
+      // Client data functions may not serialize
+      SerializeClient<Awaited<Output>>
+    :
+    // Serialize responses
+    Serialize<Awaited<Output>>
+  :
   // Back compat: manually defined data type, not inferred from loader nor action
   Jsonify<Awaited<T>>
 ;
 
+// note: cannot be inlined as logic requires union distribution
+// prettier-ignore
+type SerializeClient<Output> =
+  Output extends TypedDeferredData<infer U> ?
+    // top-level promises
+    & {
+        [K in keyof U as K extends symbol
+          ? never
+          : Promise<any> extends U[K]
+          ? K
+          : never]: DeferValueClient<U[K]>; // use generic to distribute over union
+    }
+    // non-promises
+    & {
+      [K in keyof U as Promise<any> extends U[K] ? never : K]: U[K];
+    }
+  :
+  Output extends TypedResponse<infer U> ? Jsonify<U> :
+  Awaited<Output>
+
+// prettier-ignore
+type DeferValueClient<T> =
+  T extends undefined ? undefined :
+  T extends Promise<unknown> ? Promise<Awaited<T>> :
+  T;
+
 // note: cannot be inlined as logic requires union distribution
 // prettier-ignore
 type Serialize<Output> =
@@ -49,16 +88,45 @@ type DeferValue<T> =
 
 type Pretty<T> = { [K in keyof T]: T[K] };
 
-type Loader<T> = () => Promise<
-  | TypedResponse<T> // returned responses
-  | TypedResponse<never> // thrown responses
->;
+type Loader<T> = () => Promise<TypedResponse<T>>;
 
 type LoaderDefer<T extends Record<keyof unknown, unknown>> = () => Promise<
-  | TypedDeferredData<T> // returned responses
-  | TypedResponse<never> // thrown responses
+  TypedDeferredData<T>
+>;
+
+type LoaderBoth<
+  T1 extends Record<keyof unknown, unknown>,
+  T2 extends Record<keyof unknown, unknown>
+> = () => Promise<TypedResponse<T1> | TypedDeferredData<T2>>;
+
+type ClientLoaderRaw<T extends Record<keyof unknown, unknown>> = ({
+  request,
+}: ClientLoaderFunctionArgs) => Promise<T>; // returned non-Response
+
+type ClientLoaderResponse<T extends Record<keyof unknown, unknown>> = ({
+  request,
+}: ClientLoaderFunctionArgs) => Promise<TypedResponse<T>>; // returned responses
+
+type ClientLoaderDefer<T extends Record<keyof unknown, unknown>> = ({
+  request,
+}: ClientLoaderFunctionArgs) => Promise<TypedDeferredData<T>>; // returned responses
+
+type ClientLoaderResponseAndDefer<
+  T1 extends Record<keyof unknown, unknown>,
+  T2 extends Record<keyof unknown, unknown>
+> = ({
+  request,
+}: ClientLoaderFunctionArgs) => Promise<
+  TypedResponse<T1> | TypedDeferredData<T2>
 >;
 
+type ClientLoaderRawAndDefer<
+  T1 extends Record<keyof unknown, unknown>,
+  T2 extends Record<keyof unknown, unknown>
+> = ({
+  request,
+}: ClientLoaderFunctionArgs) => Promise<T1 | TypedDeferredData<T2>>;
+
 // prettier-ignore
 // eslint-disable-next-line @typescript-eslint/no-unused-vars
 type _tests = [
@@ -78,7 +146,27 @@ type _tests = [
   Expect<Equal<Pretty<SerializeFrom<Loader<{a: string, name: number, data: boolean}>>>, {a: string, name: number, data: boolean}>>,
 
   // defer top-level promises
-  Expect<SerializeFrom<LoaderDefer<{ a: string; lazy: Promise<{ b: number }>}>> extends {a: string, lazy: Promise<{ b: number }>} ? true : false>
+  Expect<SerializeFrom<LoaderDefer<{ a: string; lazy: Promise<{ b: number }>}>> extends {a: string, lazy: Promise<{ b: number }>} ? true : false>,
+
+  // conditional defer or json
+  Expect<SerializeFrom<LoaderBoth<{ a:string, b: Promise<string> }, { c: string; lazy: Promise<{ d: number }>}>> extends { a: string, b: EmptyObject } | { c: string; lazy: Promise<{ d: number }> } ? true : false>,
+
+  // clientLoader raw JSON
+  Expect<Equal<Pretty<SerializeFrom<ClientLoaderRaw<{a: string}>>>, {a: string}>>,
+  Expect<Equal<Pretty<SerializeFrom<ClientLoaderRaw<{a: Date, b: Map<string,number> }>>>, {a: Date, b: Map<string,number>}>>,
+
+  // clientLoader json() Response
+  Expect<Equal<Pretty<SerializeFrom<ClientLoaderResponse<{a: string}>>>, {a: string}>>,
+  Expect<Equal<Pretty<SerializeFrom<ClientLoaderResponse<{a: Date}>>>, {a: string}>>,
+
+  // clientLoader defer() data
+  Expect<SerializeFrom<ClientLoaderDefer<{ a: string; lazy: Promise<{ b: number }>}>> extends {a: string, lazy: Promise<{ b: number }>} ? true : false>,
+
+  // clientLoader conditional defer or json
+  Expect<SerializeFrom<ClientLoaderResponseAndDefer<{ a: string, b: Promise<string> }, { c: string; lazy: Promise<{ d: number }>}>> extends { a: string, b: EmptyObject } | { c: string; lazy: Promise<{ d: number }> } ? true : false>,
+
+  // clientLoader conditional defer or raw
+  Expect<SerializeFrom<ClientLoaderRawAndDefer<{ a: string, b: Promise<string> }, { c: string; lazy: Promise<{ d: number }>}>> extends { a: string, b: Promise<string> } | { c: string; lazy: Promise<{ d: number }> } ? true : false>,
 ];
 
 // recursive