diff --git a/docs/docs/providers/vector_io/remote_mongodb.mdx b/docs/docs/providers/vector_io/remote_mongodb.mdx
index 8e23919b3..8564e1a5e 100644
--- a/docs/docs/providers/vector_io/remote_mongodb.mdx
+++ b/docs/docs/providers/vector_io/remote_mongodb.mdx
@@ -243,7 +243,7 @@ For general MongoDB documentation, visit [MongoDB Documentation](https://docs.mo
 
 | Field | Type | Required | Default | Description |
 |-------|------|----------|---------|-------------|
-| `connection_string` | `<class 'str'>` | No |  | MongoDB Atlas connection string (e.g., mongodb+srv://user:pass@cluster.mongodb.net/) |
+| `connection_string` | `str \| None` | No |  | MongoDB Atlas connection string (e.g., mongodb+srv://user:pass@cluster.mongodb.net/) |
 | `database_name` | `<class 'str'>` | No | llama_stack | Database name to use for vector collections |
 | `index_name` | `<class 'str'>` | No | vector_index | Name of the vector search index |
 | `path_field` | `<class 'str'>` | No | embedding | Field name for storing embeddings |
diff --git a/src/llama_stack/providers/remote/vector_io/mongodb/__init__.py b/src/llama_stack/providers/remote/vector_io/mongodb/__init__.py
index 6388c647e..d209fa3e2 100644
--- a/src/llama_stack/providers/remote/vector_io/mongodb/__init__.py
+++ b/src/llama_stack/providers/remote/vector_io/mongodb/__init__.py
@@ -14,6 +14,7 @@ async def get_adapter_impl(config: MongoDBVectorIOConfig, deps: dict[Api, Provid
 
     # Handle the deps resolution - if files API exists, pass it, otherwise None
     files_api = deps.get(Api.files)
-    impl = MongoDBVectorIOAdapter(config, deps[Api.inference], files_api)
+    models_api = deps.get(Api.models)
+    impl = MongoDBVectorIOAdapter(config, deps[Api.inference], files_api, models_api)
     await impl.initialize()
     return impl
diff --git a/src/llama_stack/providers/remote/vector_io/mongodb/config.py b/src/llama_stack/providers/remote/vector_io/mongodb/config.py
index 65ed82592..c94bf70e6 100644
--- a/src/llama_stack/providers/remote/vector_io/mongodb/config.py
+++ b/src/llama_stack/providers/remote/vector_io/mongodb/config.py
@@ -20,8 +20,9 @@ class MongoDBVectorIOConfig(BaseModel):
     """
 
     # MongoDB Atlas connection details
-    connection_string: str = Field(
-        description="MongoDB Atlas connection string (e.g., mongodb+srv://user:pass@cluster.mongodb.net/)"
+    connection_string: str | None = Field(
+        default=None,
+        description="MongoDB Atlas connection string (e.g., mongodb+srv://user:pass@cluster.mongodb.net/)",
     )
     database_name: str = Field(default="llama_stack", description="Database name to use for vector collections")
 
diff --git a/src/llama_stack/providers/remote/vector_io/mongodb/mongodb.py b/src/llama_stack/providers/remote/vector_io/mongodb/mongodb.py
index 275414746..76a77746a 100644
--- a/src/llama_stack/providers/remote/vector_io/mongodb/mongodb.py
+++ b/src/llama_stack/providers/remote/vector_io/mongodb/mongodb.py
@@ -215,7 +215,7 @@ class MongoDBIndex(EmbeddingIndex):
                         "index": self.config.index_name,
                         "queryVector": embedding.tolist(),
                         "path": self.config.path_field,
-                        "numCandidates": k * 10,  # Get more candidates for better results
+                        "numCandidates": min(k * 10, 1000),  # Cap at 1000 to prevent excessive candidates
                         "limit": k,
                     }
                 },
@@ -398,12 +398,14 @@ class MongoDBVectorIOAdapter(OpenAIVectorStoreMixin, VectorIO, VectorStoresProto
         config: MongoDBVectorIOConfig,
         inference_api,
         files_api=None,
+        models_api=None,
     ) -> None:
         # Handle the case where files_api might be a ProviderSpec that needs resolution
         resolved_files_api = files_api
         super().__init__(files_api=resolved_files_api, kvstore=None)
         self.config = config
         self.inference_api = inference_api
+        self.models_api = models_api
         self.client: MongoClient | None = None
         self.database: Database | None = None
         self.cache: dict[str, VectorStoreWithIndex] = {}
@@ -418,6 +420,13 @@ class MongoDBVectorIOAdapter(OpenAIVectorStoreMixin, VectorIO, VectorStoresProto
             if self.config.persistence:
                 self.kvstore = await kvstore_impl(self.config.persistence)
 
+            # Validate connection string
+            if not self.config.connection_string:
+                raise ValueError(
+                    "MongoDB connection_string is required but not provided. "
+                    "Please set MONGODB_CONNECTION_STRING environment variable or provide it in config."
+                )
+
             # Connect to MongoDB with optimized settings for RAG
             self.client = MongoClient(
                 self.config.connection_string,