diff --git a/.server-changes/fix-transcript-404-empty-reason-phrase.md b/.server-changes/fix-transcript-404-empty-reason-phrase.md
new file mode 100644
index 00000000000..3d129cdcac6
--- /dev/null
+++ b/.server-changes/fix-transcript-404-empty-reason-phrase.md
@@ -0,0 +1,6 @@
+---
+area: webapp
+type: fix
+---
+
+Fix missing session transcripts returning a download error instead of a not-found response
diff --git a/apps/webapp/app/services/realtime/transcriptDownload.server.test.ts b/apps/webapp/app/services/realtime/transcriptDownload.server.test.ts
index 6768b6eb0f1..4cd9c1e80da 100644
--- a/apps/webapp/app/services/realtime/transcriptDownload.server.test.ts
+++ b/apps/webapp/app/services/realtime/transcriptDownload.server.test.ts
@@ -1,4 +1,5 @@
 import { createServer, type Server } from "node:http";
+import { createServer as createTcpServer, type Server as TcpServer } from "node:net";
 import { once } from "node:events";
 import express from "express";
 import { sendRemixResponse } from "@remix-run/express/dist/server";
@@ -114,6 +115,34 @@ test("does not treat permission or service failures as an absent transcript", ()
   ).toBe(false);
   expect(isTranscriptNotFound({ $metadata: { httpStatusCode: 503 } })).toBe(false);
   expect(isTranscriptNotFound({ name: "NoSuchKey" })).toBe(true);
+  expect(isTranscriptNotFound({ status: 404, message: "Failed to download from object store: " })).toBe(
+    true
+  );
+});
+
+test("recognizes a 404 with an empty reason phrase as a missing transcript", async () => {
+  const server: TcpServer = createTcpServer((socket) => {
+    socket.once("data", () => {
+      socket.end("HTTP/1.1 404 \r\nContent-Length: 0\r\nConnection: close\r\n\r\n");
+    });
+  });
+  server.listen(0, "127.0.0.1");
+  await once(server, "listening");
+  const address = server.address();
+  if (!address || typeof address === "string") throw new Error("Expected TCP listener");
+  const baseUrl = `http://127.0.0.1:${address.port}`;
+  try {
+    const client = ObjectStoreClient.create({
+      baseUrl,
+      accessKeyId: "test",
+      secretAccessKey: "test",
+      service: "s3",
+    });
+    await expect(client.getObjectResponse(key)).rejects.toSatisfy(isTranscriptNotFound);
+  } finally {
+    server.close();
+    await once(server, "close");
+  }
 });
 
 minioTest(
diff --git a/apps/webapp/app/services/realtime/transcriptDownload.server.ts b/apps/webapp/app/services/realtime/transcriptDownload.server.ts
index da477a9ca5a..48689d06699 100644
--- a/apps/webapp/app/services/realtime/transcriptDownload.server.ts
+++ b/apps/webapp/app/services/realtime/transcriptDownload.server.ts
@@ -45,8 +45,16 @@ export function downloadTranscript(
 
 export function isTranscriptNotFound(error: unknown): boolean {
   if (!error || typeof error !== "object") return false;
-  const { name, $metadata } = error as { name?: string; $metadata?: { httpStatusCode?: number } };
+  const { name, $metadata, status } = error as {
+    name?: string;
+    $metadata?: { httpStatusCode?: number };
+    status?: unknown;
+  };
   if (name === "NoSuchKey" || name === "NotFound" || $metadata?.httpStatusCode === 404) return true;
+  // The aws4fetch adapter reports the HTTP status on the error. Check it first:
+  // S3-compatible stores may return an empty reason phrase, so the message alone
+  // cannot distinguish a 404 from other failures.
+  if (status === 404) return true;
   // The aws4fetch adapter currently reports the HTTP status text in its error.
   return (
     error instanceof Error &&
diff --git a/apps/webapp/app/v3/objectStoreClient.server.ts b/apps/webapp/app/v3/objectStoreClient.server.ts
index f7b921be0a5..acd7e039321 100644
--- a/apps/webapp/app/v3/objectStoreClient.server.ts
+++ b/apps/webapp/app/v3/objectStoreClient.server.ts
@@ -58,6 +58,24 @@ export class ObjectVersionChangedError extends Error {
   }
 }
 
+/**
+ * A failed object-store download that preserves the HTTP status code.
+ * Callers must not rely on `statusText`: S3-compatible stores may return an
+ * empty reason phrase (e.g. `HTTP/1.1 404 `), which yields an empty message
+ * suffix and breaks message-based 404 detection.
+ */
+export class ObjectStoreDownloadError extends Error {
+  readonly status: number;
+  readonly statusText: string;
+
+  constructor(message: string, status: number, statusText: string) {
+    super(message);
+    this.name = "ObjectStoreDownloadError";
+    this.status = status;
+    this.statusText = statusText;
+  }
+}
+
 /** `Range` header value for a byte range or a suffix. */
 function rangeHeader(range: { suffixLength: number } | { start: number; end: number }): string {
   return "suffixLength" in range
@@ -120,7 +138,11 @@ class Aws4FetchClient implements IObjectStoreClient {
   async getObject(key: string): Promise<string> {
     const response = await this.awsClient.fetch(this.buildUrl(key));
     if (!response.ok) {
-      throw new Error(`Failed to download from object store: ${response.statusText}`);
+      throw new ObjectStoreDownloadError(
+        `Failed to download from object store: ${response.statusText}`,
+        response.status,
+        response.statusText
+      );
     }
     return response.text();
   }
@@ -135,7 +157,11 @@ class Aws4FetchClient implements IObjectStoreClient {
   async getObjectResponse(key: string): Promise<Response> {
     const response = await this.awsClient.fetch(this.buildUrl(key));
     if (!response.ok) {
-      throw new Error(`Failed to download from object store: ${response.statusText}`);
+      throw new ObjectStoreDownloadError(
+        `Failed to download from object store: ${response.statusText}`,
+        response.status,
+        response.statusText
+      );
     }
     return response;
   }
@@ -155,7 +181,11 @@ class Aws4FetchClient implements IObjectStoreClient {
       throw new ObjectVersionChangedError(key);
     }
     if (!response.ok) {
-      throw new Error(`Failed to download range from object store: ${response.statusText}`);
+      throw new ObjectStoreDownloadError(
+        `Failed to download range from object store: ${response.statusText}`,
+        response.status,
+        response.statusText
+      );
     }
     const bytes = new Uint8Array(await response.arrayBuffer());
     return {