diff --git a/src/lib/response-wrapper.ts b/src/lib/response-wrapper.ts
index fc5e1bf..9224528 100644
--- a/src/lib/response-wrapper.ts
+++ b/src/lib/response-wrapper.ts
@@ -69,6 +69,20 @@ export class ResponseWrapper {
     this.options = options;
   }
 
+  /**
+   * Type guard to check if a value is a non-streaming response
+   */
+  private isNonStreamingResponse(value: unknown): value is models.OpenResponsesNonStreamingResponse {
+    return (
+      value !== null &&
+      typeof value === "object" &&
+      "id" in value &&
+      "object" in value &&
+      "output" in value &&
+      !("toReadableStream" in value)
+    );
+  }
+
   /**
    * Initialize the stream if not already started
    * This is idempotent - multiple calls will return the same promise
@@ -284,19 +298,57 @@ export class ResponseWrapper {
             value as EventStream<models.OpenResponsesStreamEvent>,
           );
           currentResponse = await consumeStreamForCompletion(stream);
+        } else if (this.isNonStreamingResponse(value)) {
+          currentResponse = value;
         } else {
-          currentResponse = value as models.OpenResponsesNonStreamingResponse;
+          throw new Error("Unexpected response type from API");
         }
 
         currentRound++;
       }
 
+      // Validate the final response has required fields
+      if (!currentResponse || !currentResponse.id || !currentResponse.output) {
+        throw new Error("Invalid final response: missing required fields");
+      }
+
+      // Ensure the response is in a completed state (has output content)
+      if (!Array.isArray(currentResponse.output) || currentResponse.output.length === 0) {
+        throw new Error("Invalid final response: empty or invalid output");
+      }
+
       this.finalResponse = currentResponse;
     })();
 
     return this.toolExecutionPromise;
   }
 
+  /**
+   * Internal helper to get the message after tool execution
+   */
+  private async getMessageInternal(): Promise<models.AssistantMessage> {
+    await this.executeToolsIfNeeded();
+
+    if (!this.finalResponse) {
+      throw new Error("Response not available");
+    }
+
+    return extractMessageFromResponse(this.finalResponse);
+  }
+
+  /**
+   * Internal helper to get the text after tool execution
+   */
+  private async getTextInternal(): Promise<string> {
+    await this.executeToolsIfNeeded();
+
+    if (!this.finalResponse) {
+      throw new Error("Response not available");
+    }
+
+    return extractTextFromResponse(this.finalResponse);
+  }
+
   /**
    * Get the completed message from the response.
    * This will consume the stream until completion, execute any tools, and extract the first message.
@@ -307,16 +359,7 @@ export class ResponseWrapper {
       return this.messagePromise;
     }
 
-    this.messagePromise = (async (): Promise<models.AssistantMessage> => {
-      await this.executeToolsIfNeeded();
-
-      if (!this.finalResponse) {
-        throw new Error('Response not available');
-      }
-
-      return extractMessageFromResponse(this.finalResponse);
-    })();
-
+    this.messagePromise = this.getMessageInternal();
     return this.messagePromise;
   }
 
@@ -329,16 +372,7 @@ export class ResponseWrapper {
       return this.textPromise;
     }
 
-    this.textPromise = (async () => {
-      await this.executeToolsIfNeeded();
-
-      if (!this.finalResponse) {
-        throw new Error('Response not available');
-      }
-
-      return extractTextFromResponse(this.finalResponse);
-    })();
-
+    this.textPromise = this.getTextInternal();
     return this.textPromise;
   }
 
diff --git a/src/lib/tool-orchestrator.ts b/src/lib/tool-orchestrator.ts
index 7373e58..1878386 100644
--- a/src/lib/tool-orchestrator.ts
+++ b/src/lib/tool-orchestrator.ts
@@ -80,26 +80,23 @@ export async function executeToolLoop(
       break;
     }
 
-    // Execute all tool calls
-    const roundResults: ToolExecutionResult[] = [];
-
-    for (const toolCall of toolCalls) {
+    // Execute all tool calls in parallel (parallel tool calling)
+    const toolCallPromises = toolCalls.map(async (toolCall) => {
       const tool = findToolByName(tools, toolCall.name);
 
       if (!tool) {
         // Tool not found in definitions
-        roundResults.push({
+        return {
           toolCallId: toolCall.id,
           toolName: toolCall.name,
           result: null,
           error: new Error(`Tool "${toolCall.name}" not found in tool definitions`),
-        });
-        continue;
+        } as ToolExecutionResult;
       }
 
       if (!hasExecuteFunction(tool)) {
-        // Tool has no execute function - skip
-        continue;
+        // Tool has no execute function - return null to filter out
+        return null;
       }
 
       // Build turn context
@@ -109,9 +106,34 @@ export async function executeToolLoop(
       };
 
       // Execute the tool
-      const result = await executeTool(tool, toolCall, turnContext, onPreliminaryResult);
-      roundResults.push(result);
-    }
+      return executeTool(tool, toolCall, turnContext, onPreliminaryResult);
+    });
+
+    // Wait for all tool executions to complete in parallel
+    const settledResults = await Promise.allSettled(toolCallPromises);
+
+    // Process settled results, handling both fulfilled and rejected promises
+    const roundResults: ToolExecutionResult[] = [];
+    settledResults.forEach((settled, i) => {
+      const toolCall = toolCalls[i];
+      if (!toolCall) return;
+
+      if (settled.status === "fulfilled") {
+        if (settled.value !== null) {
+          roundResults.push(settled.value);
+        }
+      } else {
+        // Promise rejected - create error result
+        roundResults.push({
+          toolCallId: toolCall.id,
+          toolName: toolCall.name,
+          result: null,
+          error: settled.reason instanceof Error
+            ? settled.reason
+            : new Error(String(settled.reason)),
+        });
+      }
+    });
 
     toolExecutionResults.push(...roundResults);