feat: wire MULTIPLE_NATIVE_TOOL_CALLS experiment to OpenAI parallel_tool_calls (#9621)

src/api/index.ts

@@ -89,6 +89,13 @@ export interface ApiHandlerCreateMessageMetadata {
 	 * Used by providers to determine whether to include native tool definitions.
 	 */
 	toolProtocol?: ToolProtocol
+	/**
+	 * Controls whether the model can return multiple tool calls in a single response.
+	 * When true, parallel tool calls are enabled (OpenAI's parallel_tool_calls=true).
+	 * When false (default), only one tool call is returned per response.
+	 * Only applies when toolProtocol is "native".
+	 */
+	parallelToolCalls?: boolean
 }
 
 export interface ApiHandler {

src/api/providers/openai-native.ts

@@ -299,10 +299,12 @@ export class OpenAiNativeHandler extends BaseProvider implements SingleCompletio
 			...(metadata?.tool_choice && { tool_choice: metadata.tool_choice }),
 		}
 
-		// For native tool protocol, explicitly disable parallel tool calls.
+		// For native tool protocol, control parallel tool calls based on the metadata flag.
+		// When parallelToolCalls is true, allow parallel tool calls (OpenAI's parallel_tool_calls=true).
+		// When false (default), explicitly disable parallel tool calls (false).
 		// For XML or when protocol is unset, omit the field entirely so the API default applies.
 		if (metadata?.toolProtocol === "native") {
-			body.parallel_tool_calls = false
+			body.parallel_tool_calls = metadata.parallelToolCalls ?? false
 		}
 
 		// Include text.verbosity only when the model explicitly supports it

src/core/task/Task.ts

@@ -3452,11 +3452,19 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 			})
 		}
 
+		// Resolve parallel tool calls setting from experiment (will move to per-API-profile setting later)
+		const parallelToolCallsEnabled = experiments.isEnabled(
+			state?.experiments ?? {},
+			EXPERIMENT_IDS.MULTIPLE_NATIVE_TOOL_CALLS,
+		)
+
 		const metadata: ApiHandlerCreateMessageMetadata = {
 			mode: mode,
 			taskId: this.taskId,
 			// Include tools and tool protocol when using native protocol and model supports it
-			...(shouldIncludeTools ? { tools: allTools, tool_choice: "auto", toolProtocol } : {}),
+			...(shouldIncludeTools
+				? { tools: allTools, tool_choice: "auto", toolProtocol, parallelToolCalls: parallelToolCallsEnabled }
+				: {}),
 		}
 
 		// Create an AbortController to allow cancelling the request mid-stream