diff --git a/frontend-modern/src/api/ai.ts b/frontend-modern/src/api/ai.ts
index 6aa3649..afc4d19 100644
--- a/frontend-modern/src/api/ai.ts
+++ b/frontend-modern/src/api/ai.ts
@@ -55,7 +55,7 @@ export class AIAPI {
     return apiFetchJSON(`${this.baseUrl}/ai/cost/reset`, {
       method: 'POST',
       body: JSON.stringify({}),
-    }) as Promise<{ ok: boolean }>;
+    }) as Promise<{ ok: boolean; backup_file?: string }>;
   }
 
   // Start OAuth flow for Claude Pro/Max subscription
diff --git a/frontend-modern/src/components/AI/AICostDashboard.tsx b/frontend-modern/src/components/AI/AICostDashboard.tsx
index 19fca74..0b6ba96 100644
--- a/frontend-modern/src/components/AI/AICostDashboard.tsx
+++ b/frontend-modern/src/components/AI/AICostDashboard.tsx
@@ -187,10 +187,14 @@ export const AICostDashboard: Component = () => {
   };
 
   const resetHistory = async () => {
-    if (!confirm('Reset AI usage history? This clears the stored token/cost history.')) return;
+    if (!confirm('Reset AI usage history? A backup will be created in the Pulse config directory.')) return;
     try {
-      await AIAPI.resetCostHistory();
-      notificationStore.success('AI usage history reset');
+      const result = await AIAPI.resetCostHistory();
+      if (result.backup_file) {
+        notificationStore.success(`AI usage history reset (backup: ${result.backup_file})`);
+      } else {
+        notificationStore.success('AI usage history reset');
+      }
       await loadSummary(days());
     } catch (err) {
       logger.error('[AICostDashboard] Failed to reset AI cost history:', err);
diff --git a/internal/api/ai_handlers.go b/internal/api/ai_handlers.go
index 256b470..4659cd3 100644
--- a/internal/api/ai_handlers.go
+++ b/internal/api/ai_handlers.go
@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"os"
+	"path/filepath"
 	"strings"
 	"sync"
 	"time"
@@ -2460,13 +2462,36 @@ func (h *AISettingsHandler) HandleResetAICostHistory(w http.ResponseWriter, r *h
 		return
 	}
 
+	backupFile := ""
+	if h.persistence != nil {
+		configDir := h.persistence.DataDir()
+		if strings.TrimSpace(configDir) != "" {
+			usagePath := filepath.Join(configDir, "ai_usage_history.json")
+			if _, err := os.Stat(usagePath); err == nil {
+				ts := time.Now().UTC().Format("20060102-150405")
+				backupFile = fmt.Sprintf("ai_usage_history.json.bak-%s", ts)
+				backupPath := filepath.Join(configDir, backupFile)
+				if err := os.Rename(usagePath, backupPath); err != nil {
+					log.Error().Err(err).Str("path", usagePath).Msg("Failed to backup AI usage history before reset")
+					http.Error(w, "Failed to backup AI usage history", http.StatusInternalServerError)
+					return
+				}
+			}
+		}
+	}
+
 	if err := h.aiService.ClearCostHistory(); err != nil {
 		log.Error().Err(err).Msg("Failed to clear AI cost history")
 		http.Error(w, "Failed to clear AI cost history", http.StatusInternalServerError)
 		return
 	}
 
-	if err := utils.WriteJSONResponse(w, map[string]any{"ok": true}); err != nil {
+	resp := map[string]any{"ok": true}
+	if backupFile != "" {
+		resp["backup_file"] = backupFile
+	}
+
+	if err := utils.WriteJSONResponse(w, resp); err != nil {
 		log.Error().Err(err).Msg("Failed to write clear cost history response")
 	}
 }