diff --git a/packages/core/src/evaluation/providers/pi-cli.ts b/packages/core/src/evaluation/providers/pi-cli.ts
index bf8307015..fb1434127 100644
--- a/packages/core/src/evaluation/providers/pi-cli.ts
+++ b/packages/core/src/evaluation/providers/pi-cli.ts
@@ -638,17 +638,9 @@ function extractMessages(events: unknown[]): readonly Message[] {
   if (messages) {
     for (let i = messages.length - 1; i >= 0; i--) {
       if (messages[i].role === 'assistant' && !messages[i].content) {
-        // Try to find content from the last message_end event
-        for (let j = events.length - 1; j >= 0; j--) {
-          const evt = events[j] as Record<string, unknown> | null;
-          if (!evt || evt.type !== 'message_end') continue;
-          const msg = evt.message as Record<string, unknown> | undefined;
-          if (msg?.role !== 'assistant') continue;
-          const text = extractPiTextContent(msg.content);
-          if (text) {
-            messages[i] = { ...messages[i], content: text };
-            break;
-          }
+        const recoveredContent = extractAssistantContentFromEvents(events);
+        if (recoveredContent) {
+          messages[i] = { ...messages[i], content: recoveredContent };
         }
         break;
       }
@@ -667,6 +659,42 @@ function extractMessages(events: unknown[]): readonly Message[] {
   return messages;
 }
 
+function extractAssistantContentFromEvents(events: unknown[]): string | undefined {
+  for (let i = events.length - 1; i >= 0; i--) {
+    const evt = events[i] as Record<string, unknown> | null;
+    if (!evt || typeof evt !== 'object') continue;
+
+    if (evt.type === 'message_end') {
+      const msg = evt.message as Record<string, unknown> | undefined;
+      if (msg?.role !== 'assistant') continue;
+      const text = extractPiTextContent(msg.content);
+      if (text) return text;
+      continue;
+    }
+
+    if (evt.type !== 'message_update') continue;
+
+    const msg = evt.message as Record<string, unknown> | undefined;
+    if (msg?.role !== 'assistant') continue;
+
+    const deltaEvent = evt.assistantMessageEvent as Record<string, unknown> | undefined;
+    const partial = deltaEvent?.partial as Record<string, unknown> | undefined;
+
+    const partialText = extractPiTextContent(partial?.content);
+    if (partialText) return partialText;
+
+    if (typeof deltaEvent?.content === 'string' && deltaEvent.content.length > 0) {
+      return deltaEvent.content;
+    }
+
+    if (typeof deltaEvent?.delta === 'string' && deltaEvent.delta.length > 0) {
+      return deltaEvent.delta;
+    }
+  }
+
+  return undefined;
+}
+
 /**
  * Scan JSONL events for tool_execution_start / tool_execution_end pairs and
  * reconstruct ToolCall objects from them.
diff --git a/packages/core/test/evaluation/providers/pi-cli-tool-extraction.test.ts b/packages/core/test/evaluation/providers/pi-cli-tool-extraction.test.ts
index 84e5d0d6a..4269ffe00 100644
--- a/packages/core/test/evaluation/providers/pi-cli-tool-extraction.test.ts
+++ b/packages/core/test/evaluation/providers/pi-cli-tool-extraction.test.ts
@@ -228,4 +228,44 @@ describe('pi-cli tool call extraction from events', () => {
       path: '.agents/skills/csv-analyzer/SKILL.md',
     });
   });
+
+  it('should recover assistant text from message_update deltas when agent_end content is empty', () => {
+    const events = [
+      {
+        type: 'message_update',
+        message: { role: 'assistant', content: [] },
+        assistantMessageEvent: {
+          type: 'text_delta',
+          contentIndex: 0,
+          delta: '2 + 2',
+          partial: { role: 'assistant', content: [{ type: 'text', text: '2 + 2' }] },
+        },
+      },
+      {
+        type: 'message_update',
+        message: { role: 'assistant', content: [] },
+        assistantMessageEvent: {
+          type: 'text_delta',
+          contentIndex: 0,
+          delta: ' = 4',
+          partial: { role: 'assistant', content: [{ type: 'text', text: '2 + 2 = 4' }] },
+        },
+      },
+      {
+        type: 'agent_end',
+        messages: [
+          { role: 'user', content: [{ type: 'text', text: 'What is 2+2?' }] },
+          { role: 'assistant', content: [] },
+        ],
+      },
+    ];
+
+    const messages = extractMessages(events);
+
+    expect(messages).toHaveLength(2);
+    expect(messages[1]).toMatchObject({
+      role: 'assistant',
+      content: '2 + 2 = 4',
+    });
+  });
 });