diff --git a/package-lock.json b/package-lock.json
index fe62311..9cbcab1 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9,7 +9,7 @@
       "version": "1.0.0",
       "license": "ISC",
       "dependencies": {
-        "@copilot-extensions/preview-sdk": "^3.0.0",
+        "@copilot-extensions/preview-sdk": "^4.0.0",
         "openai": "^4.55.0"
       },
       "devDependencies": {
@@ -20,9 +20,9 @@
       }
     },
     "node_modules/@copilot-extensions/preview-sdk": {
-      "version": "3.0.0",
-      "resolved": "https://registry.npmjs.org/@copilot-extensions/preview-sdk/-/preview-sdk-3.0.0.tgz",
-      "integrity": "sha512-iFzQFlYgNr4jc0ciiBuGya4Zua/ozATxNhU9YHTBpSONPKpGJ6bDcc7Z8xmCi2baNAzMPeJQaIoXVyEgeo74eQ==",
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/@copilot-extensions/preview-sdk/-/preview-sdk-4.0.0.tgz",
+      "integrity": "sha512-0qazOleLhjJFU9iRWQ19PIws4xC3/SFLqPWSbKlUeXxHTo38w1gdfmi1BF68ndA59wRCJSMIMlYbc5trG/dEJw==",
       "license": "MIT",
       "dependencies": {
         "@octokit/request": "^9.1.3",
diff --git a/package.json b/package.json
index 3b00d61..2aa6d9c 100644
--- a/package.json
+++ b/package.json
@@ -12,7 +12,7 @@
   "license": "ISC",
   "description": "",
   "dependencies": {
-    "@copilot-extensions/preview-sdk": "^3.0.0",
+    "@copilot-extensions/preview-sdk": "^4.0.0",
     "openai": "^4.55.0"
   },
   "devDependencies": {
diff --git a/src/index.ts b/src/index.ts
index 58a3f24..3dfc87f 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -119,7 +119,7 @@ const server = createServer(async (request, response) => {
       response.write(chunkStr);
     }
 
-    response.end(createDoneEvent().toString());
+    response.end(createDoneEvent());
     return;
   }
 
@@ -167,7 +167,7 @@ const server = createServer(async (request, response) => {
       response.write(chunkStr);
     }
 
-    response.end(createDoneEvent().toString());
+    response.end(createDoneEvent());
     console.timeEnd("streaming");
   } catch (err) {
     console.error(err);
@@ -189,7 +189,7 @@ function getBody(request: IncomingMessage): Promise<string> {
         bodyParts.push(chunk);
       })
       .on("end", () => {
-        body = Buffer.concat(bodyParts).toString();
+        body = Buffer.concat(bodyParts);
         resolve(body);
       });
   });