diff --git a/src/lib/server/ai.ts b/src/lib/server/ai.ts
index ff424b4..3c4a7dc 100644
--- a/src/lib/server/ai.ts
+++ b/src/lib/server/ai.ts
@@ -320,6 +320,7 @@ export async function gradeSubmissionWithAgent(
 		finalRun = await processRunStream(thread.id, initialStream, roomId);
 	} catch (err) {
 		logger.error(`Agent streaming failed on thread ${thread.id}:`, err);
+		client.agents.deleteThread(thread.id);
 		return fallbackGrade(submission, task);
 	}
 
@@ -331,6 +332,8 @@ export async function gradeSubmissionWithAgent(
 	const match = raw.match(/\{[\s\S]*\}$/);
 	const jsonText = match ? match[0] : raw;
 
+	client.agents.deleteThread(thread.id);
+
 	try {
 		const parsed = JSON.parse(jsonText) as OpenAIResponse;
 		if (parsed.grade === 'HUMAN_REVIEW_REQUIRED') {
@@ -376,6 +379,7 @@ export async function resumeAgentWithHumanReview(
 		finalRun = await processRunStream(threadId, stream, roomId);
 	} catch (err) {
 		logger.error(`Agent streaming failed on thread ${threadId}:`, err);
+		client.agents.deleteThread(threadId);
 		return fallbackGrade('', '');
 	}
 
@@ -387,6 +391,8 @@ export async function resumeAgentWithHumanReview(
 	const match = raw.match(/\{[\s\S]*\}$/);
 	const jsonText = match ? match[0] : raw;
 
+	client.agents.deleteThread(threadId);
+
 	try {
 		const parsed = JSON.parse(jsonText) as OpenAIResponse;
 		return parsed;