diff --git a/src/index.ts b/src/index.ts
index 3299ca3..aab41ce 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -37,8 +37,10 @@ export type {
   SDKResultMessage,
   SDKStreamEventMessage,
   PermissionMode,
-  PermissionResult,
   CanUseToolCallback,
+  CanUseToolResponse,
+  CanUseToolResponseAllow,
+  CanUseToolResponseDeny,
 } from "./types.js";
 
 export { Session } from "./session.js";
diff --git a/src/session.ts b/src/session.ts
index e6f2629..f38183d 100644
--- a/src/session.ts
+++ b/src/session.ts
@@ -137,16 +137,16 @@ export class Session implements AsyncDisposable {
     if (this.options.canUseTool) {
       try {
         const result = await this.options.canUseTool(req.tool_name, req.input);
-        if (result.allow) {
+        if (result.behavior === "allow") {
           response = {
             behavior: "allow",
-            updatedInput: null, // TODO: not supported
+            updatedInput: result.updatedInput ?? null,
             updatedPermissions: [], // TODO: not implemented
           } satisfies CanUseToolResponseAllow;
         } else {
           response = {
             behavior: "deny",
-            message: result.reason ?? "Denied by canUseTool callback",
+            message: result.message ?? "Denied by canUseTool callback",
             interrupt: false, // TODO: not wired up yet
           } satisfies CanUseToolResponseDeny;
         }
diff --git a/src/types.ts b/src/types.ts
index 19ee6ea..93edb17 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -24,8 +24,8 @@ export type {
   CreateBlock,
 } from "@letta-ai/letta-code/protocol";
 
-// Import types for use in SessionOptions
-import type { CreateBlock } from "@letta-ai/letta-code/protocol";
+// Import types for use in this file
+import type { CreateBlock, CanUseToolResponse } from "@letta-ai/letta-code/protocol";
 
 // ═══════════════════════════════════════════════════════════════
 // SYSTEM PROMPT TYPES
@@ -86,20 +86,12 @@ export type MemoryPreset = "persona" | "human" | "project";
 // ═══════════════════════════════════════════════════════════════
 
 /**
- * Result of a canUseTool callback
- */
-export interface PermissionResult {
-  allow: boolean;
-  reason?: string;
-}
-
-/**
- * Callback for custom permission handling
+ * Callback for custom permission handling.
  */
 export type CanUseToolCallback = (
   toolName: string,
   toolInput: Record<string, unknown>,
-) => Promise<PermissionResult> | PermissionResult;
+) => Promise<CanUseToolResponse> | CanUseToolResponse;
 
 /**
  * Options for creating a session