no topk for openai test

crates/lingua/src/processing/transform.rs

@@ -1188,6 +1188,74 @@ mod tests {
         assert!(output.get("top_p").is_none(), "Should not have top_p");
     }
 
+    #[test]
+    #[cfg(all(feature = "openai", feature = "google"))]
+    fn test_google_top_k_openai_model_drops_top_k_for_chat_completions() {
+        let payload = json!({
+            "contents": [{
+                "role": "user",
+                "parts": [{"text": "Write a short sentence about API gateways."}]
+            }],
+            "generationConfig": {
+                "topK": 1,
+                "maxOutputTokens": 1024
+            }
+        });
+        let input = to_bytes(&payload);
+
+        let result =
+            transform_request(input, ProviderFormat::ChatCompletions, Some("gpt-5-nano")).unwrap();
+
+        let output: Value = crate::serde_json::from_slice(result.as_bytes()).unwrap();
+        assert_eq!(result.source_format(), Some(ProviderFormat::Google));
+        assert_eq!(
+            output.get("model").and_then(Value::as_str),
+            Some("gpt-5-nano")
+        );
+        assert!(
+            output.get("top_k").is_none(),
+            "OpenAI Chat Completions should not receive top_k"
+        );
+        assert_eq!(
+            output.get("max_completion_tokens").and_then(Value::as_i64),
+            Some(1024)
+        );
+    }
+
+    #[test]
+    #[cfg(all(feature = "openai", feature = "google"))]
+    fn test_google_top_k_openai_model_drops_top_k_for_responses() {
+        let payload = json!({
+            "contents": [{
+                "role": "user",
+                "parts": [{"text": "Write a short sentence about API gateways."}]
+            }],
+            "generationConfig": {
+                "topK": 1,
+                "maxOutputTokens": 1024
+            }
+        });
+        let input = to_bytes(&payload);
+
+        let result =
+            transform_request(input, ProviderFormat::Responses, Some("gpt-5-nano")).unwrap();
+
+        let output: Value = crate::serde_json::from_slice(result.as_bytes()).unwrap();
+        assert_eq!(result.source_format(), Some(ProviderFormat::Google));
+        assert_eq!(
+            output.get("model").and_then(Value::as_str),
+            Some("gpt-5-nano")
+        );
+        assert!(
+            output.get("top_k").is_none(),
+            "OpenAI Responses should not receive top_k"
+        );
+        assert_eq!(
+            output.get("max_output_tokens").and_then(Value::as_i64),
+            Some(1024)
+        );
+    }
+
     #[test]
     #[cfg(feature = "openai")]
     fn test_non_reasoning_model_still_passthroughs() {

payloads/cases/params.ts

@@ -1505,6 +1505,25 @@ export const paramsCases: TestCaseCollection = {
     bedrock: null,
   },
 
+  googleOpenAIModelTopKParam: {
+    "chat-completions": null,
+    responses: null,
+    anthropic: null,
+    google: {
+      contents: [
+        {
+          role: "user",
+          parts: [{ text: "Write a short sentence about API gateways." }],
+        },
+      ],
+      generationConfig: {
+        topK: 1,
+        maxOutputTokens: 1024,
+      },
+    },
+    bedrock: null,
+  },
+
   streamParam: {
     "chat-completions": null,
     responses: null,