diff --git a/genkit-tools/common/src/types/model.ts b/genkit-tools/common/src/types/model.ts
index c052d9ab46..a36d9f288f 100644
--- a/genkit-tools/common/src/types/model.ts
+++ b/genkit-tools/common/src/types/model.ts
@@ -372,7 +372,7 @@ export const GenerateActionOutputConfig = z.object({
 
 export const GenerateActionOptionsSchema = z.object({
   /** A model name (e.g. `vertexai/gemini-1.0-pro`). */
-  model: z.string(),
+  model: z.string().optional(),
   /** Retrieved documents to be used as context for this generation. */
   docs: z.array(DocumentDataSchema).optional(),
   /** Conversation history for multi-turn prompting when supported by the underlying model. */
diff --git a/genkit-tools/genkit-schema.json b/genkit-tools/genkit-schema.json
index 0ee8e76519..3897cade85 100644
--- a/genkit-tools/genkit-schema.json
+++ b/genkit-tools/genkit-schema.json
@@ -469,7 +469,6 @@
         }
       },
       "required": [
-        "model",
         "messages"
       ],
       "additionalProperties": false
diff --git a/py/packages/genkit/src/genkit/core/typing.py b/py/packages/genkit/src/genkit/core/typing.py
index 40baffe314..5330e7459c 100644
--- a/py/packages/genkit/src/genkit/core/typing.py
+++ b/py/packages/genkit/src/genkit/core/typing.py
@@ -951,7 +951,7 @@ class GenerateActionOptions(BaseModel):
     """Model for generateactionoptions data."""
 
     model_config = ConfigDict(extra='forbid', populate_by_name=True)
-    model: str
+    model: str | None = None
     docs: list[DocumentData] | None = None
     messages: list[Message]
     tools: list[str] | None = None