diff --git a/rust/cocoindex/src/base/json_schema.rs b/rust/cocoindex/src/base/json_schema.rs
index e001e9dfe..1a663337e 100644
--- a/rust/cocoindex/src/base/json_schema.rs
+++ b/rust/cocoindex/src/base/json_schema.rs
@@ -21,6 +21,10 @@ pub struct ToJsonSchemaOptions {
 
     /// If true, the top level must be a JSON object.
     pub top_level_must_be_object: bool,
+
+    /// If true, include `additionalProperties: false` in object schemas.
+    /// Some LLM APIs (e.g., Gemini) do not support this constraint and will error.
+    pub supports_additional_properties: bool,
 }
 
 struct JsonSchemaBuilder {
@@ -263,7 +267,11 @@ impl JsonSchemaBuilder {
                 .filter(|&f| self.options.fields_always_required || !f.value_type.nullable)
                 .map(|f| f.name.to_string())
                 .collect(),
-            additional_properties: Some(Schema::Bool(false).into()),
+            additional_properties: if self.options.supports_additional_properties {
+                Some(Schema::Bool(false).into())
+            } else {
+                None
+            },
             ..Default::default()
         }));
         schema
@@ -406,6 +414,7 @@ mod tests {
             supports_format: true,
             extract_descriptions: false,
             top_level_must_be_object: false,
+            supports_additional_properties: true,
         }
     }
 
@@ -415,6 +424,7 @@ mod tests {
             supports_format: true,
             extract_descriptions: true,
             top_level_must_be_object: false,
+            supports_additional_properties: true,
         }
     }
 
@@ -424,6 +434,7 @@ mod tests {
             supports_format: true,
             extract_descriptions: false,
             top_level_must_be_object: false,
+            supports_additional_properties: true,
         }
     }
 
@@ -433,6 +444,7 @@ mod tests {
             supports_format: true,
             extract_descriptions: false,
             top_level_must_be_object: true,
+            supports_additional_properties: true,
         }
     }
 
@@ -1357,6 +1369,7 @@ mod tests {
             supports_format: false,
             extract_descriptions: false,
             top_level_must_be_object: false,
+            supports_additional_properties: true,
         };
         let result = build_json_schema(value_type, options).unwrap();
         let json_schema = schema_to_json(&result.schema);
@@ -1396,6 +1409,7 @@ mod tests {
             supports_format: true,
             extract_descriptions: false, // We want to see the description in the schema
             top_level_must_be_object: false,
+            supports_additional_properties: true,
         };
 
         let result = build_json_schema(enriched_value_type, options).unwrap();
diff --git a/rust/cocoindex/src/llm/anthropic.rs b/rust/cocoindex/src/llm/anthropic.rs
index c84e2c483..3a3b4baa1 100644
--- a/rust/cocoindex/src/llm/anthropic.rs
+++ b/rust/cocoindex/src/llm/anthropic.rs
@@ -164,6 +164,7 @@ impl LlmGenerationClient for Client {
             supports_format: false,
             extract_descriptions: false,
             top_level_must_be_object: true,
+            supports_additional_properties: true,
         }
     }
 }
diff --git a/rust/cocoindex/src/llm/bedrock.rs b/rust/cocoindex/src/llm/bedrock.rs
index 0f5f99035..00baccd45 100644
--- a/rust/cocoindex/src/llm/bedrock.rs
+++ b/rust/cocoindex/src/llm/bedrock.rs
@@ -174,6 +174,7 @@ impl LlmGenerationClient for Client {
             supports_format: false,
             extract_descriptions: false,
             top_level_must_be_object: true,
+            supports_additional_properties: true,
         }
     }
 }
diff --git a/rust/cocoindex/src/llm/gemini.rs b/rust/cocoindex/src/llm/gemini.rs
index 0e6ce1bce..cd1b49e8d 100644
--- a/rust/cocoindex/src/llm/gemini.rs
+++ b/rust/cocoindex/src/llm/gemini.rs
@@ -49,24 +49,6 @@ impl AiStudioClient {
     }
 }
 
-// Recursively remove all `additionalProperties` fields from a JSON value
-fn remove_additional_properties(value: &mut Value) {
-    match value {
-        Value::Object(map) => {
-            map.remove("additionalProperties");
-            for v in map.values_mut() {
-                remove_additional_properties(v);
-            }
-        }
-        Value::Array(arr) => {
-            for v in arr {
-                remove_additional_properties(v);
-            }
-        }
-        _ => {}
-    }
-}
-
 impl AiStudioClient {
     fn get_api_url(&self, model: &str, api_name: &str) -> String {
         format!(
@@ -149,8 +131,7 @@ impl LlmGenerationClient for AiStudioClient {
 
         // If structured output is requested, add schema and responseMimeType
         if let Some(OutputFormat::JsonSchema { schema, .. }) = &request.output_format {
-            let mut schema_json = serde_json::to_value(schema)?;
-            remove_additional_properties(&mut schema_json);
+            let schema_json = serde_json::to_value(schema)?;
             payload["generationConfig"] = serde_json::json!({
                 "responseMimeType": "application/json",
                 "responseSchema": schema_json
@@ -181,6 +162,7 @@ impl LlmGenerationClient for AiStudioClient {
             supports_format: false,
             extract_descriptions: false,
             top_level_must_be_object: true,
+            supports_additional_properties: false,
         }
     }
 }
@@ -379,6 +361,7 @@ impl LlmGenerationClient for VertexAiClient {
             supports_format: false,
             extract_descriptions: false,
             top_level_must_be_object: true,
+            supports_additional_properties: false,
         }
     }
 }
diff --git a/rust/cocoindex/src/llm/ollama.rs b/rust/cocoindex/src/llm/ollama.rs
index b02a6ddc3..35c93bfc8 100644
--- a/rust/cocoindex/src/llm/ollama.rs
+++ b/rust/cocoindex/src/llm/ollama.rs
@@ -120,6 +120,7 @@ impl LlmGenerationClient for Client {
             supports_format: true,
             extract_descriptions: true,
             top_level_must_be_object: false,
+            supports_additional_properties: true,
         }
     }
 }
diff --git a/rust/cocoindex/src/llm/openai.rs b/rust/cocoindex/src/llm/openai.rs
index 67a23be35..853166a2a 100644
--- a/rust/cocoindex/src/llm/openai.rs
+++ b/rust/cocoindex/src/llm/openai.rs
@@ -162,6 +162,7 @@ impl LlmGenerationClient for Client {
             supports_format: false,
             extract_descriptions: false,
             top_level_must_be_object: true,
+            supports_additional_properties: true,
         }
     }
 }