diff --git a/js/ai/src/prompt.ts b/js/ai/src/prompt.ts
index 1c489ad189..29e2b6cf7f 100644
--- a/js/ai/src/prompt.ts
+++ b/js/ai/src/prompt.ts
@@ -116,6 +116,7 @@ export interface PromptConfig<
   input?: {
     schema?: I;
     jsonSchema?: JSONSchema7;
+    default?: Record<string, any>;
   };
   system?: string | Part | Part[] | PartsResolver<z.infer<I>>;
   prompt?: string | Part | Part[] | PartsResolver<z.infer<I>>;
@@ -331,8 +332,8 @@ function definePromptAsync<
           },
           metadata: resolvedOptions.metadata?.metadata
             ? {
-                prompt: resolvedOptions.metadata?.metadata,
-              }
+              prompt: resolvedOptions.metadata?.metadata,
+            }
             : undefined,
         });
 
@@ -432,6 +433,7 @@ function promptMetadata(options: PromptConfig<any, any, any>) {
       ...options.metadata?.prompt,
       config: options.config,
       input: {
+        default: options.input?.default,
         schema: options.input ? toJsonSchema(options.input) : undefined,
       },
       name: options.name.includes('.')
@@ -855,6 +857,7 @@ function loadPrompt(
           format: promptMetadata.output?.format,
         },
         input: {
+          default: promptMetadata.input?.default,
           jsonSchema: promptMetadata.input?.schema,
         },
         metadata,
diff --git a/py/samples/framework-evaluator-demo/prompts/hello.prompt b/py/samples/framework-evaluator-demo/prompts/hello.prompt
index c51d31d169..8d0913e0b6 100644
--- a/py/samples/framework-evaluator-demo/prompts/hello.prompt
+++ b/py/samples/framework-evaluator-demo/prompts/hello.prompt
@@ -1,8 +1,11 @@
 ---
+model: googleai/gemini-3-flash-preview
 config:
   temperature: 0.75
   topK: 10
 input:
+  default:
+    query: "fibonacci function"
   schema:
     query: string
 ---
diff --git a/py/samples/framework-prompt-demo/prompts/recipe.prompt b/py/samples/framework-prompt-demo/prompts/recipe.prompt
index a8f4bf4bc1..5754817b42 100644
--- a/py/samples/framework-prompt-demo/prompts/recipe.prompt
+++ b/py/samples/framework-prompt-demo/prompts/recipe.prompt
@@ -1,6 +1,8 @@
 ---
 model: googleai/gemini-3-flash-preview
 input:
+  default:
+    food: "banana bread"
   schema:
     food: string
     ingredients?(array): string
diff --git a/py/samples/framework-prompt-demo/prompts/story.prompt b/py/samples/framework-prompt-demo/prompts/story.prompt
index 981317bfb1..8a08d626c5 100644
--- a/py/samples/framework-prompt-demo/prompts/story.prompt
+++ b/py/samples/framework-prompt-demo/prompts/story.prompt
@@ -1,6 +1,9 @@
 ---
 model: googleai/gemini-3-flash-preview
 input:
+  default:
+    subject: "a brave little toaster"
+    personality: "courageous"
   schema:
     subject: string
     personality?: string
diff --git a/py/samples/web-endpoints-hello/prompts/code_review.prompt b/py/samples/web-endpoints-hello/prompts/code_review.prompt
index ee636421ac..fbc7f9e8af 100644
--- a/py/samples/web-endpoints-hello/prompts/code_review.prompt
+++ b/py/samples/web-endpoints-hello/prompts/code_review.prompt
@@ -1,6 +1,9 @@
 ---
 model: googleai/gemini-3-flash-preview
 input:
+  default:
+    code: "def add(a, b):\n    return a + b"
+    language: "python"
   schema:
     code: string
     language?: string