diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index b16976047f..63cc6dd801 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -728,14 +728,19 @@ export namespace SessionPrompt {
         system.push(STRUCTURED_OUTPUT_SYSTEM_PROMPT)
       }
 
-      // altimate_change start - trace system prompt
-      Tracer.active?.logSpan({
-        name: "system-prompt",
-        startTime: Date.now(),
-        endTime: Date.now(),
-        input: { agent: agent.name, step },
-        output: { parts: system.length, content: system.join("\n\n") },
-      })
+      // altimate_change start - trace system prompt once per loop() call.
+      // The system prompt is functionally identical across steps within a single
+      // loop() invocation (same agent, same environment). Agent switches re-enter
+      // loop() with step reset to 0, so each agent's prompt is traced separately.
+      if (step === 1) {
+        Tracer.active?.logSpan({
+          name: "system-prompt",
+          startTime: Date.now(),
+          endTime: Date.now(),
+          input: { agent: agent.name, step },
+          output: { parts: system.length, content: system.join("\n\n") },
+        })
+      }
       // altimate_change end
 
       const result = await processor.process({