diff --git a/js/ai/src/generate.ts b/js/ai/src/generate.ts
index 8d9a1766f..c609b4860 100755
--- a/js/ai/src/generate.ts
+++ b/js/ai/src/generate.ts
@@ -377,6 +377,10 @@ export async function generate<
     returnToolRequests: resolvedOptions.returnToolRequests,
     maxTurns: resolvedOptions.maxTurns,
   };
+  // if config is empty and it was not explicitly passed in, we delete it, don't want {}
+  if (Object.keys(params.config).length === 0 && !resolvedOptions.config) {
+    delete params.config;
+  }
 
   return await runWithStreamingCallback(
     registry,
diff --git a/js/ai/src/generate/action.ts b/js/ai/src/generate/action.ts
index 2dc71bf8a..7e8065c42 100644
--- a/js/ai/src/generate/action.ts
+++ b/js/ai/src/generate/action.ts
@@ -218,6 +218,7 @@ function applyTransferPreamble(
     ],
     toolChoice: transferPreamble.toolChoice || rawRequest.toolChoice,
     tools: transferPreamble.tools || rawRequest.tools,
+    config: transferPreamble.config || rawRequest.config,
   });
 }
 
diff --git a/js/ai/src/prompt.ts b/js/ai/src/prompt.ts
index 58efc1ad7..c49e51f9b 100644
--- a/js/ai/src/prompt.ts
+++ b/js/ai/src/prompt.ts
@@ -293,7 +293,7 @@ function definePromptAsync<
       docs = resolvedOptions.docs;
     }
 
-    return stripUndefinedProps({
+    const opts: GenerateOptions = stripUndefinedProps({
       model: resolvedOptions.model,
       maxTurns: resolvedOptions.maxTurns,
       messages,
@@ -310,6 +310,11 @@ function definePromptAsync<
         ...renderOptions?.config,
       },
     });
+    // if config is empty and it was not explicitly passed in, we delete it, don't want {}
+    if (Object.keys(opts.config).length === 0 && !renderOptions?.config) {
+      delete opts.config;
+    }
+    return opts;
   };
   const rendererActionConfig = lazy(() =>
     optionsPromise.then((options: PromptConfig<I, O, CustomOptions>) => {
diff --git a/js/core/src/reflection.ts b/js/core/src/reflection.ts
index 5cbb4ae61..feb1f39a6 100644
--- a/js/core/src/reflection.ts
+++ b/js/core/src/reflection.ts
@@ -20,7 +20,11 @@ import getPort, { makeRange } from 'get-port';
 import { Server } from 'http';
 import path from 'path';
 import * as z from 'zod';
-import { Status, StatusCodes, runWithStreamingCallback } from './action.js';
+import {
+  StatusCodes,
+  runWithStreamingCallback,
+  type Status,
+} from './action.js';
 import { GENKIT_REFLECTION_API_SPEC_VERSION, GENKIT_VERSION } from './index.js';
 import { logger } from './logging.js';
 import { Registry } from './registry.js';
diff --git a/js/genkit/tests/chat_test.ts b/js/genkit/tests/chat_test.ts
index 501ede1b3..7be76ded7 100644
--- a/js/genkit/tests/chat_test.ts
+++ b/js/genkit/tests/chat_test.ts
@@ -290,8 +290,7 @@ describe('preamble', () => {
     assert.deepStrictEqual(text, 'hi from agent b (toolChoice: required)');
     assert.deepStrictEqual(pm.lastRequest, {
       config: {
-        // TODO: figure out if config should be swapped out as well...
-        temperature: 2,
+        temperature: 1,
       },
       messages: [
         {
diff --git a/js/genkit/tests/prompts_test.ts b/js/genkit/tests/prompts_test.ts
index 3f4ea276e..14f4dbf83 100644
--- a/js/genkit/tests/prompts_test.ts
+++ b/js/genkit/tests/prompts_test.ts
@@ -676,7 +676,6 @@ describe('definePrompt', () => {
       const response = await hi.render({ name: 'Genkit' });
       delete response.model; // ignore
       assert.deepStrictEqual(response, {
-        config: {},
         messages: [{ content: [{ text: 'hi Genkit' }], role: 'user' }],
       });
     });
@@ -978,7 +977,6 @@ describe('definePrompt', () => {
       const response = await hi.render({ name: 'Genkit' });
       delete response.model; // ignore
       assert.deepStrictEqual(response, {
-        config: {},
         messages: [
           {
             content: [
@@ -1369,8 +1367,8 @@ describe('asTool', () => {
 
     assert.deepStrictEqual(text, 'hi from agent b');
     assert.deepStrictEqual(pm.lastRequest, {
+      // Original config, toolPrompt has no config.
       config: {
-        // TODO: figure out if config should be swapped out as well...
         temperature: 2,
       },
       messages: [