diff --git a/src/helpers/zod.ts b/src/helpers/zod.ts
index 67057b60d2..35353f82c2 100644
--- a/src/helpers/zod.ts
+++ b/src/helpers/zod.ts
@@ -333,18 +333,8 @@ export function zodTextFormat<ZodInput extends ZodTypeLike>(
   );
 }
 
-/**
- * Creates a chat completion `function` tool that can be invoked
- * automatically by the chat completion `.runTools()` method or automatically
- * parsed by `.parse()` / `.stream()`.
- *
- * Arguments are converted to strict JSON Schema and validated with the supplied
- * Zod schema before the optional callback receives them.
- *
- * @param options Model-visible function name, Zod parameter schema, description,
- * and optional callback used by `chat.completions.runTools()`.
- */
-export function zodFunction<Parameters extends ZodTypeLike>(options: {
+/** Model-facing settings and an optional execution callback for a Zod function tool. */
+interface ZodFunctionOptions<Parameters extends ZodTypeLike> {
   /** Model-visible function name used to identify matching tool calls. */
   name: string;
 
@@ -356,19 +346,52 @@ export function zodFunction<Parameters extends ZodTypeLike>(options: {
 
   /** Optional model-visible explanation of when and how the function should be used. */
   description?: string | undefined;
-}): AutoParseableTool<{
+}
+
+/** A Zod function tool retaining its inferred argument and callback types. */
+type ZodFunctionTool<
+  Parameters extends ZodTypeLike,
+  Callback extends ZodFunctionOptions<Parameters>['function'],
+> = AutoParseableTool<{
   /** Inferred argument type produced by the Zod parameter schema. */
   arguments: InferZodType<Parameters>;
-
   /** Model-visible name used to match generated function calls. */
   name: string;
+  /** Callback availability determines whether the tool can be executed. */
+  function: Callback;
+}>;
 
-  /** Callback signature associated with validated function-call arguments. */
-  function: (args: InferZodType<Parameters>) => unknown;
-}> {
+/**
+ * Creates a chat completion `function` tool that can be invoked automatically
+ * by `.runTools()` or parsed by `.parse()` / `.stream()`.
+ *
+ * Arguments are converted to strict JSON Schema and validated with the supplied
+ * Zod schema before the callback receives them.
+ *
+ * @param options Model-visible function name, Zod parameter schema, description,
+ * and callback used by `chat.completions.runTools()`.
+ */
+export function zodFunction<Parameters extends ZodTypeLike>(
+  options: ZodFunctionOptions<Parameters> & {
+    /** Callback invoked with validated arguments by chat `runTools()`. */
+    function: NonNullable<ZodFunctionOptions<Parameters>['function']>;
+  },
+): ZodFunctionTool<Parameters, NonNullable<ZodFunctionOptions<Parameters>['function']>>;
+
+/**
+ * Creates a strict chat completion function tool for `.parse()` / `.stream()`.
+ * Without a guaranteed callback, the tool cannot be executed by `.runTools()`.
+ *
+ * @param options Model-visible function details and an optional callback.
+ */
+export function zodFunction<Parameters extends ZodTypeLike>(
+  options: ZodFunctionOptions<Parameters>,
+): ZodFunctionTool<Parameters, ZodFunctionOptions<Parameters>['function']>;
+
+/** Builds a strict Chat Completions function tool from the supplied Zod schema. */
+export function zodFunction<Parameters extends ZodTypeLike>(options: ZodFunctionOptions<Parameters>) {
   const zodSchema = options.parameters as unknown as ZodSchema;
 
-  // @ts-expect-error TODO
   return makeParseableTool<any>(
     {
       type: 'function',
diff --git a/tests/helpers/zod.test.ts b/tests/helpers/zod.test.ts
index c569321a76..f10d97cf3e 100644
--- a/tests/helpers/zod.test.ts
+++ b/tests/helpers/zod.test.ts
@@ -1,4 +1,5 @@
 import { vi } from 'vitest';
+import type OpenAI from 'openai';
 import { hasOwn } from 'openai/internal/utils/values';
 
 import {
@@ -794,7 +795,7 @@ describe.each([
   }
 });
 
-function _typeTests() {
+function _typeTests(client: OpenAI, maybeCallback?: (args: { hello: 'world' }) => unknown) {
   const MiniSchema = zv4Mini.object({ hello: zv4Mini.literal('world') });
   type ParsedArguments = { hello: 'world' };
 
@@ -817,4 +818,51 @@ function _typeTests() {
   compareType<Parameters<NonNullable<typeof responseTool.$callback>>[0], ParsedArguments>(true);
   compareType<ReturnType<typeof responseTool.$parseRaw>, ParsedArguments>(true);
   compareType<typeof responseTool.__arguments, ParsedArguments>(true);
+
+  const explicitGenericTool = zodFunction<typeof MiniSchema>({
+    name: 'explicit_generic',
+    parameters: MiniSchema,
+    function: (args) => {
+      expectType<ParsedArguments>(args);
+      return Promise.resolve(args);
+    },
+  });
+  expectType<true>(explicitGenericTool.__hasFunction);
+  expectType<false>(
+    zodFunction<typeof MiniSchema>({ name: 'explicit_parse_only', parameters: MiniSchema }).__hasFunction,
+  );
+
+  for (const parameters of [
+    zv3.object({ hello: zv3.literal('world') }),
+    zv4.object({ hello: zv4.literal('world') }),
+    MiniSchema,
+  ]) {
+    const options = { name: 'greet', parameters };
+    const runnable = zodFunction({
+      ...options,
+      function: (args) => expectType<ParsedArguments>(args),
+    });
+    const callbackless = zodFunction(options);
+    const undefinedCallback = zodFunction({ ...options, function: undefined });
+    const optionalCallback = zodFunction({ ...options, function: maybeCallback });
+
+    expectType<true>(runnable.__hasFunction);
+    expectType<false>(callbackless.__hasFunction);
+    expectType<false>(undefinedCallback.__hasFunction);
+    expectType<false>(optionalCallback.__hasFunction);
+    expectType<ParsedArguments>(callbackless.__arguments);
+
+    const request = { model: 'gpt-4o', messages: [] };
+    client.chat.completions.runTools({ ...request, tools: [runnable] });
+    client.chat.completions.runTools({ ...request, tools: [runnable], stream: true });
+
+    for (const tool of [callbackless, undefinedCallback, optionalCallback]) {
+      client.chat.completions.parse({ ...request, tools: [tool] });
+      client.chat.completions.stream({ ...request, tools: [tool] });
+      // @ts-expect-error a tool without a guaranteed callback cannot be executed
+      client.chat.completions.runTools({ ...request, tools: [tool] });
+      // @ts-expect-error streaming tool execution also requires a guaranteed callback
+      client.chat.completions.runTools({ ...request, tools: [tool], stream: true });
+    }
+  }
 }