diff --git a/ui/src/app/api/files/[...filePath]/route.ts b/ui/src/app/api/files/[...filePath]/route.ts
index f9ebba12..40874d0c 100644
--- a/ui/src/app/api/files/[...filePath]/route.ts
+++ b/ui/src/app/api/files/[...filePath]/route.ts
@@ -2,6 +2,7 @@
 import { NextRequest, NextResponse } from 'next/server';
 import fs from 'fs';
 import path from 'path';
+import { Readable } from 'stream';
 import { getDatasetsRoot, getTrainingFolder } from '@/server/settings';
 
 export async function GET(request: NextRequest, { params }: { params: { filePath: string } }) {
@@ -85,19 +86,27 @@ export async function GET(request: NextRequest, { params }: { params: { filePath
     };
 
     if (range) {
-      // Parse range header
+      // Parse range header. An open-ended range (`bytes=0-`) must serve to EOF —
+      // capping it forces clients into serial re-requests and RTT-bound throughput.
       const parts = range.replace(/bytes=/, '').split('-');
       const start = parseInt(parts[0], 10);
-      const end = parts[1] ? parseInt(parts[1], 10) : Math.min(start + 10 * 1024 * 1024, stat.size - 1); // 10MB chunks
+      const end = parts[1] ? parseInt(parts[1], 10) : stat.size - 1;
+
+      if (isNaN(start) || isNaN(end) || start > end || start >= stat.size) {
+        return new NextResponse('Range Not Satisfiable', {
+          status: 416,
+          headers: { 'Content-Range': `bytes */${stat.size}` },
+        });
+      }
       const chunkSize = end - start + 1;
 
       const fileStream = fs.createReadStream(resolvedFilePath, {
         start,
         end,
-        highWaterMark: 64 * 1024, // 64KB buffer
+        highWaterMark: 4 * 1024 * 1024, // large buffer to minimize per-chunk overhead
       });
 
-      return new NextResponse(fileStream as any, {
+      return new NextResponse(Readable.toWeb(fileStream) as any, {
         status: 206,
         headers: {
           ...commonHeaders,
@@ -106,12 +115,11 @@ export async function GET(request: NextRequest, { params }: { params: { filePath
         },
       });
     } else {
-      // For full file download, read directly without streaming wrapper
       const fileStream = fs.createReadStream(resolvedFilePath, {
-        highWaterMark: 64 * 1024, // 64KB buffer
+        highWaterMark: 4 * 1024 * 1024, // large buffer to minimize per-chunk overhead
       });
 
-      return new NextResponse(fileStream as any, {
+      return new NextResponse(Readable.toWeb(fileStream) as any, {
         headers: {
           ...commonHeaders,
           'Content-Length': String(stat.size),