diff --git a/RenderPipeline2.md b/RenderPipeline2.md
index b995c68..ed34a41 100644
--- a/RenderPipeline2.md
+++ b/RenderPipeline2.md
@@ -1194,7 +1194,7 @@ Renders run past the cut at each end (8 + 8 by house convention). Handles ship w
 The Standard review MP4 is AE's H.264 (UHD, ~35 Mbps). ProRes itself can't be the player's source — only Safari on a Mac decodes it in a web page, and UHD ProRes LT is ~280 Mbps — so the worker (≥ 1.7.0, when `preview.highQuality` is on) adds two things after the AE render, both **best-effort** (a failure costs the extras, never the preview):
 
 - **High quality MP4:** ffmpeg re-encodes the delivery MOV as full-res H.264 High, CRF 14 capped at 100 Mbps, yuv420p, faststart → `Version.hqFileUrl`. The player shows an **HQ** switch when present; switching keeps frame, play state, speed and zoom, is remembered per browser (`review:quality`), and falls back to Standard if the file won't load. Same comp as the Standard MP4, so slate and handles line up frame for frame.
-- **ProRes download:** the MOV itself is uploaded (presign kind `highres`) → `Version.highResKey/highResFilename/highResSize`. It is the version's **High Res** download in the client portal (named with the client code, `clientHighResFilename`) and a **ProRes** button on the staff review page. The shot's manually uploaded High Res remains the fallback for versions without one. Since worker 1.7.1 the MOV uploads **in the background after finalize** (`HighResUploader`, queue in `%ProgramData%\VFXReviewWorker\highres-queue`, resumes after a restart, 5 attempts) and attaches via `POST /api/ext/render/jobs/{id}/attach-highres` (E13b); a MOV from a preview that a newer preview has superseded is discarded. While a preview job uploads, the worker replaces the job's log tail with live upload status.
+- **ProRes download:** the MOV itself is uploaded (presign kind `highres`) → `Version.highResKey/highResFilename/highResSize`. It is the version's **High Res** download in the client portal (named with the client code, `clientHighResFilename`) and a **ProRes** button on the staff review page. The shot's manually uploaded High Res remains the fallback for versions without one. Since worker 1.7.1 the MOV uploads **in the background after finalize** (`HighResUploader`, queue in `%ProgramData%\VFXReviewWorker\highres-queue`, resumes after a restart, 5 attempts) and attaches via `POST /api/ext/render/jobs/{id}/attach-highres` (E13b); a MOV from a preview that a newer preview has superseded is discarded. While a preview job uploads, the worker replaces the job's log tail with live upload status. Since 1.7.2, artifacts of 16 MB or more upload as S3 multipart: `artifact-presign` with `multipart: true, size` returns `uploadId`, `partSize` (8 MB minimum) and one presigned URL per part; the worker PUTs parts on `uploadConcurrency` connections (default 16), retries each part up to 4 times, then calls `artifact-complete` (E20b) to stitch them, or with `abort: true` to discard them. A single connection from the studio to nbg1 is capped near 0.1 MB/s.
 
 A lease keep-alive runs during the encode and uploads (they can outlast the 300 s lease). The export timeline records what was attached.
 
diff --git a/RenderWorker/README.md b/RenderWorker/README.md
index 30460aa..42c99d3 100644
--- a/RenderWorker/README.md
+++ b/RenderWorker/README.md
@@ -208,6 +208,9 @@ read back from the assembly, so a machine can never report a version it is not r
 `pathMappings` translate the manifest's canonical UNC paths to this machine's drive
 mappings. `plateSearchRoots` is optional: it is only consulted when a manifest carries no
 timing plate (older panel versions), to find the shot's plates for the timecode check.
+`uploadConcurrency` (default 16) is how many parallel connections a file of 16 MB or more
+uploads over. Each connection to object storage is capped near 0.1 MB/s from the studio, so
+throughput scales with it (measured 2026-10-01: 1 → 0.13 MB/s, 8 → 0.64, 24 → 1.69 MB/s).
 Everything tunable (poll interval, lease, stall timeout, max attempts, validation) lives in
 the server's SystemConfig and arrives at registration — no per-machine tuning files.
 
diff --git a/RenderWorker/VFXReviewWorker.Tests/MultipartUploadTests.cs b/RenderWorker/VFXReviewWorker.Tests/MultipartUploadTests.cs
new file mode 100644
index 0000000..b5571c4
--- /dev/null
+++ b/RenderWorker/VFXReviewWorker.Tests/MultipartUploadTests.cs
@@ -0,0 +1,205 @@
+using System.Collections.Concurrent;
+using System.Net;
+using System.Net.Sockets;
+using System.Text.Json;
+using Microsoft.Extensions.Logging.Abstractions;
+using VFXReviewWorker;
+using Xunit;
+
+namespace VFXReviewWorker.Tests;
+
+/// <summary>
+/// Large artifacts go up as parallel multipart parts: from the studio a single
+/// connection to object storage is capped near 0.1 MB/s, so a ProRes MOV could
+/// not finish inside the 30 min request timeout. These drive the real upload
+/// code against a local fake of the server + storage.
+/// </summary>
+public class MultipartUploadTests : IDisposable
+{
+    private const int PartSize = 8 * 1024 * 1024;
+
+    private readonly HttpListener _listener = new();
+    private readonly string _base;
+    private readonly ConcurrentDictionary<int, byte[]> _parts = new();
+    private readonly ConcurrentDictionary<int, int> _failuresLeft = new();
+    private readonly ConcurrentBag<string> _completions = new();
+    private int _inFlight, _maxInFlight;
+    private bool _multipartSupported = true;
+    private byte[]? _singlePut;
+
+    public MultipartUploadTests()
+    {
+        var port = FreePort();
+        _base = $"http://localhost:{port}/";
+        _listener.Prefixes.Add(_base);
+        _listener.Start();
+        _ = Task.Run(Serve);
+    }
+
+    private static int FreePort()
+    {
+        var l = new TcpListener(IPAddress.Loopback, 0);
+        l.Start();
+        var port = ((IPEndPoint)l.LocalEndpoint).Port;
+        l.Stop();
+        return port;
+    }
+
+    private async Task Serve()
+    {
+        while (_listener.IsListening)
+        {
+            HttpListenerContext ctx;
+            try { ctx = await _listener.GetContextAsync(); } catch { return; }
+            _ = Task.Run(() => Handle(ctx));
+        }
+    }
+
+    private async Task Handle(HttpListenerContext ctx)
+    {
+        var path = ctx.Request.Url!.AbsolutePath;
+        using var ms = new MemoryStream();
+        await ctx.Request.InputStream.CopyToAsync(ms);
+        var body = ms.ToArray();
+        var res = ctx.Response;
+
+        if (path.EndsWith("/artifact-presign"))
+        {
+            var req = JsonDocument.Parse(body).RootElement;
+            var size = req.GetProperty("size").GetInt64();
+            object payload = _multipartSupported && req.GetProperty("multipart").GetBoolean()
+                ? new
+                {
+                    key = "highres/x.mov",
+                    uploadId = "up1",
+                    partSize = PartSize,
+                    partUrls = Enumerable.Range(1, (int)((size + PartSize - 1) / PartSize))
+                        .Select(n => $"{_base}part/{n}").ToList(),
+                }
+                : new { key = "highres/x.mov", presignedUrl = $"{_base}single" };
+            await Json(res, payload);
+        }
+        else if (path.StartsWith("/part/"))
+        {
+            var n = int.Parse(path["/part/".Length..]);
+            var now = Interlocked.Increment(ref _inFlight);
+            InterlockedMax(ref _maxInFlight, now);
+            await Task.Delay(50);
+            Interlocked.Decrement(ref _inFlight);
+            if (_failuresLeft.TryGetValue(n, out var left) && left > 0)
+            {
+                _failuresLeft[n] = left - 1;
+                res.StatusCode = 500;
+                res.Close();
+                return;
+            }
+            _parts[n] = body;
+            res.Headers["ETag"] = $"\"etag-{n}\"";
+            res.Close();
+        }
+        else if (path == "/single")
+        {
+            _singlePut = body;
+            res.Close();
+        }
+        else if (path.EndsWith("/artifact-complete"))
+        {
+            _completions.Add(System.Text.Encoding.UTF8.GetString(body));
+            await Json(res, new { ok = true });
+        }
+        else
+        {
+            res.StatusCode = 404;
+            res.Close();
+        }
+    }
+
+    private static void InterlockedMax(ref int target, int value)
+    {
+        int seen;
+        while ((seen = Volatile.Read(ref target)) < value && Interlocked.CompareExchange(ref target, value, seen) != seen) { }
+    }
+
+    private static async Task Json(HttpListenerResponse res, object payload)
+    {
+        var bytes = JsonSerializer.SerializeToUtf8Bytes(payload, WorkerOptions.JsonOpts);
+        res.ContentType = "application/json";
+        await res.OutputStream.WriteAsync(bytes);
+        res.Close();
+    }
+
+    private ApiClient Client(int concurrency = 4) =>
+        new(new WorkerOptions { ServerUrl = _base, ApiKey = "k", UploadConcurrency = concurrency },
+            NullLogger<ApiClient>.Instance);
+
+    private static string TempFile(int bytes)
+    {
+        var path = Path.GetTempFileName();
+        var data = new byte[bytes];
+        new Random(42).NextBytes(data);
+        File.WriteAllBytes(path, data);
+        return path;
+    }
+
+    [Fact]
+    public async Task Uploads_parts_in_parallel_and_stitches_them_in_order()
+    {
+        var file = TempFile(PartSize * 5 + 12345);
+        long lastProgress = 0;
+        var key = await Client(4).UploadArtifactAsync("job1", "m1", "highres", file, "video/quicktime",
+            CancellationToken.None, sent => Interlocked.Exchange(ref lastProgress, sent));
+
+        Assert.Equal("highres/x.mov", key);
+        var stitched = Enumerable.Range(1, 6).SelectMany(n => _parts[n]).ToArray();
+        Assert.Equal(File.ReadAllBytes(file), stitched);
+        Assert.True(_maxInFlight > 1, "parts should upload concurrently");
+        Assert.True(_maxInFlight <= 4, "concurrency is capped by UploadConcurrency");
+        Assert.Equal(new FileInfo(file).Length, Interlocked.Read(ref lastProgress));
+
+        var complete = JsonDocument.Parse(Assert.Single(_completions)).RootElement;
+        Assert.False(complete.TryGetProperty("abort", out _));
+        Assert.Equal(6, complete.GetProperty("parts").GetArrayLength());
+        Assert.Equal("\"etag-1\"", complete.GetProperty("parts")[0].GetProperty("etag").GetString());
+        File.Delete(file);
+    }
+
+    [Fact]
+    public async Task A_failed_part_is_retried_on_its_own()
+    {
+        var file = TempFile(PartSize * 3);
+        _failuresLeft[2] = 2;
+        var key = await Client().UploadArtifactAsync("job1", "m1", "highres", file, "video/quicktime", CancellationToken.None);
+
+        Assert.NotNull(key);
+        Assert.Equal(File.ReadAllBytes(file), Enumerable.Range(1, 3).SelectMany(n => _parts[n]).ToArray());
+        File.Delete(file);
+    }
+
+    [Fact]
+    public async Task A_part_that_keeps_failing_aborts_the_upload()
+    {
+        var file = TempFile(PartSize * 3);
+        _failuresLeft[3] = 99;
+        var key = await Client().UploadArtifactAsync("job1", "m1", "highres", file, "video/quicktime", CancellationToken.None);
+
+        Assert.Null(key);
+        var abort = JsonDocument.Parse(Assert.Single(_completions)).RootElement;
+        Assert.True(abort.GetProperty("abort").GetBoolean());
+        File.Delete(file);
+    }
+
+    [Fact]
+    public async Task Falls_back_to_a_single_put_on_a_server_without_multipart()
+    {
+        _multipartSupported = false;
+        var file = TempFile(PartSize * 3);
+        var key = await Client().UploadArtifactAsync("job1", "m1", "highres", file, "video/quicktime", CancellationToken.None);
+
+        Assert.Equal("highres/x.mov", key);
+        Assert.Equal(File.ReadAllBytes(file), _singlePut);
+        Assert.Empty(_completions);
+        File.Delete(file);
+    }
+
+    public void Dispose() => _listener.Close();
+}
diff --git a/RenderWorker/VFXReviewWorker/ApiClient.cs b/RenderWorker/VFXReviewWorker/ApiClient.cs
index 5c7c9bb..26bf8c5 100644
--- a/RenderWorker/VFXReviewWorker/ApiClient.cs
+++ b/RenderWorker/VFXReviewWorker/ApiClient.cs
@@ -13,10 +13,16 @@ namespace VFXReviewWorker;
 public sealed class ApiClient
 {
     private readonly HttpClient _http;
+    private readonly WorkerOptions _options;
     private readonly ILogger<ApiClient> _log;
 
+    // Presigned uploads: a separate client so the URL is not sent with our
+    // Authorization header, and a generous per-request timeout for media.
+    private static readonly HttpClient _upload = new() { Timeout = TimeSpan.FromMinutes(30) };
+
     public ApiClient(WorkerOptions options, ILogger<ApiClient> log)
     {
+        _options = options;
         _log = log;
         _http = new HttpClient
         {
@@ -170,6 +176,8 @@ public sealed class ApiClient
                 kind,
                 fileName = Path.GetFileName(filePath),
                 contentType,
+                multipart = size >= MultipartThreshold,
+                size,
             }, Json, ct);
             if (!presignRes.IsSuccessStatusCode)
             {
@@ -179,17 +187,23 @@ public sealed class ApiClient
             var presign = await presignRes.Content.ReadFromJsonAsync<PresignResponse>(Json, ct);
             if (presign is null) return null;
 
-            // Media files can be large — generous timeout, separate client so the
-            // presigned URL is not sent with our Authorization header.
-            using var upload = new HttpClient { Timeout = TimeSpan.FromMinutes(30) };
-            await using var stream = File.OpenRead(filePath);
-            var content = new ProgressStreamContent(stream, onProgress);
-            content.Headers.ContentType = new MediaTypeHeaderValue(contentType);
-            var putRes = await upload.PutAsync(presign.PresignedUrl, content, ct);
-            if (!putRes.IsSuccessStatusCode)
+            if (presign.UploadId is not null && presign.PartUrls is { Count: > 0 } && presign.PartSize > 0)
             {
-                _log.LogWarning("Upload of {Kind} failed after {Sec:F0}s: {Status}", kind, sw.Elapsed.TotalSeconds, (int)putRes.StatusCode);
-                return null;
+                if (!await UploadMultipartAsync(jobId, machineId, kind, filePath, size, presign, onProgress, ct))
+                    return null;
+            }
+            else
+            {
+                // Single PUT: small files, or a server that predates multipart.
+                await using var stream = File.OpenRead(filePath);
+                var content = new ProgressStreamContent(stream, onProgress);
+                content.Headers.ContentType = new MediaTypeHeaderValue(contentType);
+                var putRes = await _upload.PutAsync(presign.PresignedUrl, content, ct);
+                if (!putRes.IsSuccessStatusCode)
+                {
+                    _log.LogWarning("Upload of {Kind} failed after {Sec:F0}s: {Status}", kind, sw.Elapsed.TotalSeconds, (int)putRes.StatusCode);
+                    return null;
+                }
             }
             if (kind != "log")
                 _log.LogInformation("Uploaded {Kind} for job {JobId} in {Sec:F0}s ({Speed:F1} MB/s)",
@@ -203,6 +217,117 @@ public sealed class ApiClient
         }
     }
 
+    // Files at least this big go up as parallel multipart parts (E20b).
+    private const long MultipartThreshold = 16L * 1024 * 1024;
+    private const int PartAttempts = 4;
+
+    /// <summary>
+    /// Uploads the parts concurrently (UploadConcurrency connections), each
+    /// retried on its own so a dropped connection costs one part, not the
+    /// file; then asks the server to stitch them. Aborts on failure so the
+    /// stored parts don't linger in the bucket.
+    /// </summary>
+    private async Task<bool> UploadMultipartAsync(string jobId, string machineId, string kind, string filePath,
+        long size, PresignResponse presign, Action<long>? onProgress, CancellationToken ct)
+    {
+        var partUrls = presign.PartUrls!;
+        var partSize = presign.PartSize;
+        var etags = new string?[partUrls.Count];
+        var sentPerPart = new long[partUrls.Count];
+        long sentTotal = 0;
+        var next = -1;
+
+        using var handle = File.OpenHandle(filePath, FileMode.Open, FileAccess.Read, FileShare.Read, FileOptions.Asynchronous);
+        using var failed = CancellationTokenSource.CreateLinkedTokenSource(ct);
+
+        async Task Worker()
+        {
+            int i;
+            while ((i = Interlocked.Increment(ref next)) < partUrls.Count && !failed.IsCancellationRequested)
+            {
+                var offset = i * partSize;
+                var len = (int)Math.Min(partSize, size - offset);
+                var buffer = new byte[len];
+                var read = 0;
+                while (read < len) read += await RandomAccess.ReadAsync(handle, buffer.AsMemory(read), offset + read, failed.Token);
+
+                for (var attempt = 1; ; attempt++)
+                {
+                    var part = i;
+                    // Progress restarts from zero for a retried part.
+                    Interlocked.Add(ref sentTotal, -Interlocked.Exchange(ref sentPerPart[part], 0));
+                    var content = new ProgressStreamContent(new MemoryStream(buffer, writable: false), sent =>
+                    {
+                        var delta = sent - Interlocked.Exchange(ref sentPerPart[part], sent);
+                        onProgress?.Invoke(Interlocked.Add(ref sentTotal, delta));
+                    });
+                    try
+                    {
+                        var res = await _upload.PutAsync(partUrls[i], content, failed.Token);
+                        var etag = res.Headers.ETag?.Tag
+                                   ?? (res.Headers.TryGetValues("ETag", out var v) ? v.FirstOrDefault() : null);
+                        if (res.IsSuccessStatusCode && etag is not null)
+                        {
+                            etags[i] = etag;
+                            break;
+                        }
+                        _log.LogWarning("Part {Part}/{Count} of {Kind} for job {JobId} failed: {Status} (attempt {N}/{Max})",
+                            i + 1, partUrls.Count, kind, jobId, (int)res.StatusCode, attempt, PartAttempts);
+                    }
+                    catch (Exception ex) when (!failed.IsCancellationRequested)
+                    {
+                        _log.LogWarning("Part {Part}/{Count} of {Kind} for job {JobId} failed: {Error} (attempt {N}/{Max})",
+                            i + 1, partUrls.Count, kind, jobId, ex.Message, attempt, PartAttempts);
+                    }
+                    if (attempt >= PartAttempts)
+                    {
+                        failed.Cancel(); // no point finishing the other parts
+                        return;
+                    }
+                    await Task.Delay(TimeSpan.FromSeconds(5 * attempt), failed.Token);
+                }
+            }
+        }
+
+        var concurrency = Math.Clamp(_options.UploadConcurrency, 1, 64);
+        try
+        {
+            await Task.WhenAll(Enumerable.Range(0, Math.Min(concurrency, partUrls.Count)).Select(_ => Task.Run(Worker)));
+        }
+        catch (OperationCanceledException)
+        {
+            // a part gave up, or shutdown — either way the upload is aborted below
+        }
+
+        var complete = !failed.IsCancellationRequested && etags.All(e => e is not null);
+        if (complete)
+        {
+            var res = await _http.PostAsJsonAsync($"api/ext/render/jobs/{jobId}/artifact-complete", new
+            {
+                machineId,
+                key = presign.Key,
+                uploadId = presign.UploadId,
+                parts = etags.Select((etag, i) => new { partNumber = i + 1, etag }),
+            }, Json, ct);
+            if (res.IsSuccessStatusCode) return true;
+            _log.LogWarning("Completing multipart {Kind} for job {JobId} failed: {Status} {Body}",
+                kind, jobId, (int)res.StatusCode, await res.Content.ReadAsStringAsync(ct));
+        }
+
+        try
+        {
+            await _http.PostAsJsonAsync($"api/ext/render/jobs/{jobId}/artifact-complete", new
+            {
+                machineId,
+                key = presign.Key,
+                uploadId = presign.UploadId,
+                abort = true,
+            }, Json, CancellationToken.None);
+        }
+        catch { /* parts expire on their own */ }
+        return false;
+    }
+
     public Task<string?> UploadLogAsync(string jobId, string machineId, string logFilePath, CancellationToken ct) =>
         UploadArtifactAsync(jobId, machineId, "log", logFilePath, "text/plain", ct);
 
diff --git a/RenderWorker/VFXReviewWorker/Dtos.cs b/RenderWorker/VFXReviewWorker/Dtos.cs
index 8974ab1..fd2e574 100644
--- a/RenderWorker/VFXReviewWorker/Dtos.cs
+++ b/RenderWorker/VFXReviewWorker/Dtos.cs
@@ -304,6 +304,11 @@ public sealed class PresignResponse
     public string PresignedUrl { get; set; } = "";
     public string Key { get; set; } = "";
     public string Url { get; set; } = "";
+    // Multipart (server ≥ 1.7.2 contract) — absent from older servers, which
+    // only ever return PresignedUrl.
+    public string? UploadId { get; set; }
+    public long PartSize { get; set; }
+    public List<string>? PartUrls { get; set; }
 }
 
 public sealed class ExportDetailResponse
diff --git a/RenderWorker/VFXReviewWorker/VFXReviewWorker.csproj b/RenderWorker/VFXReviewWorker/VFXReviewWorker.csproj
index b9295fa..7132811 100644
--- a/RenderWorker/VFXReviewWorker/VFXReviewWorker.csproj
+++ b/RenderWorker/VFXReviewWorker/VFXReviewWorker.csproj
@@ -15,7 +15,7 @@
       every change that gets published. publish.ps1 appends the git SHA via
       SourceRevisionId, giving "1.1.0+feb1c7b".
     -->
-    <Version>1.7.1</Version>
+    <Version>1.7.2</Version>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/RenderWorker/VFXReviewWorker/WorkerOptions.cs b/RenderWorker/VFXReviewWorker/WorkerOptions.cs
index a87c611..732fad1 100644
--- a/RenderWorker/VFXReviewWorker/WorkerOptions.cs
+++ b/RenderWorker/VFXReviewWorker/WorkerOptions.cs
@@ -35,6 +35,12 @@ public sealed class WorkerOptions
     /// </summary>
     public List<string> PlateSearchRoots { get; set; } = new();
     /// <summary>
+    /// Parallel connections per large upload. From the studio each connection
+    /// to object storage is capped near 0.1 MB/s, so throughput scales with
+    /// this (measured: 1 → 0.13 MB/s, 8 → 0.64, 24 → 1.69).
+    /// </summary>
+    public int UploadConcurrency { get; set; } = 16;
+    /// <summary>
     /// Read from the assembly, not from config.json: a hand-maintained version
     /// string is exactly the thing that goes stale, and a machine reporting a
     /// version it is not running is worse than no version at all.
diff --git a/app/api/ext/render/jobs/[jobId]/artifact-complete/route.ts b/app/api/ext/render/jobs/[jobId]/artifact-complete/route.ts
new file mode 100644
index 0000000..9f27032
--- /dev/null
+++ b/app/api/ext/render/jobs/[jobId]/artifact-complete/route.ts
@@ -0,0 +1,62 @@
+import { NextRequest, NextResponse } from "next/server";
+import { isExtAuthorized } from "@/lib/render-pipeline/ext-auth";
+import { toErrorResponse, PipelineError } from "@/lib/render-pipeline/errors";
+import { isArtifactKey } from "@/lib/render-pipeline/artifact-kinds";
+import { db } from "@/lib/db";
+import { abortHetznerMultipartUpload, completeHetznerMultipartUpload } from "@/lib/storage";
+
+// ── POST /api/ext/render/jobs/{jobId}/artifact-complete (E20b) ───────────────
+//
+// Closes a multipart upload started by artifact-presign: stitches the parts
+// (by part number + ETag) into the final object, or with `abort: true` throws
+// the stored parts away after the worker gave up.
+
+export async function POST(
+  req: NextRequest,
+  { params }: { params: Promise<{ jobId: string }> }
+) {
+  if (!isExtAuthorized(req)) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
+  }
+  const { jobId } = await params;
+  let body: {
+    machineId?: string;
+    key?: string;
+    uploadId?: string;
+    parts?: { partNumber?: number; etag?: string }[];
+    abort?: boolean;
+  };
+  try {
+    body = await req.json();
+  } catch {
+    return NextResponse.json({ error: "Invalid JSON" }, { status: 400 });
+  }
+  try {
+    if (!body.machineId) throw new PipelineError(400, "machineId is required");
+    if (!body.key || !isArtifactKey(body.key)) throw new PipelineError(422, "key is not a worker artifact key");
+    if (!body.uploadId) throw new PipelineError(400, "uploadId is required");
+
+    const job = await db.renderJob.findUnique({ where: { id: jobId }, select: { machineId: true } });
+    if (!job) throw new PipelineError(404, "Render job not found");
+    if (job.machineId !== body.machineId) {
+      throw new PipelineError(409, "Job is not held by this machine (lease reassigned?)");
+    }
+
+    if (body.abort) {
+      await abortHetznerMultipartUpload(body.key, body.uploadId);
+      return NextResponse.json({ ok: true, aborted: true });
+    }
+
+    const parts = (body.parts ?? []).filter(
+      (p): p is { partNumber: number; etag: string } =>
+        typeof p.partNumber === "number" && typeof p.etag === "string" && p.etag.length > 0
+    );
+    if (parts.length === 0) throw new PipelineError(422, "parts are required");
+
+    await completeHetznerMultipartUpload(body.key, body.uploadId, parts);
+    return NextResponse.json({ ok: true, key: body.key, url: `/api/files/${body.key}` });
+  } catch (err) {
+    const { body: errBody, status } = toErrorResponse(err);
+    return NextResponse.json(errBody, { status });
+  }
+}
diff --git a/app/api/ext/render/jobs/[jobId]/artifact-presign/route.ts b/app/api/ext/render/jobs/[jobId]/artifact-presign/route.ts
index fd326cd..2f62e05 100644
--- a/app/api/ext/render/jobs/[jobId]/artifact-presign/route.ts
+++ b/app/api/ext/render/jobs/[jobId]/artifact-presign/route.ts
@@ -3,7 +3,12 @@ import { randomUUID } from "crypto";
 import { isExtAuthorized } from "@/lib/render-pipeline/ext-auth";
 import { toErrorResponse, PipelineError } from "@/lib/render-pipeline/errors";
 import { db } from "@/lib/db";
-import { generateHetznerPresignedUploadUrl, sanitizeFileName } from "@/lib/storage";
+import { ARTIFACT_KIND_FOLDERS } from "@/lib/render-pipeline/artifact-kinds";
+import {
+  createHetznerMultipartUpload,
+  generateHetznerPresignedUploadUrl,
+  sanitizeFileName,
+} from "@/lib/storage";
 
 // ── POST /api/ext/render/jobs/{jobId}/artifact-presign (E20) ─────────────────
 //
@@ -11,14 +16,16 @@ import { generateHetznerPresignedUploadUrl, sanitizeFileName } from "@/lib/stora
 // storage folder layout: preview → videos/, thumbnail → image/,
 // metadata/log → renders/, highres (the delivery MOV) → highres/ beside the
 // manually uploaded High Res files.
+//
+// `multipart: true` + `size` (worker ≥ 1.7.2) returns an S3 multipart upload
+// instead — an uploadId and one presigned URL per part — which the worker
+// fills in parallel and closes with artifact-complete (E20b). A single PUT
+// from the studio is capped near 0.1 MB/s; parallel parts scale with the
+// number of connections. Older workers never ask and get the single PUT.
 
-const KIND_FOLDERS: Record<string, string> = {
-  preview: "videos",
-  thumbnail: "image",
-  metadata: "renders",
-  log: "renders",
-  highres: "highres",
-};
+const KIND_FOLDERS = ARTIFACT_KIND_FOLDERS;
+const MIN_PART = 8 * 1024 * 1024;
+const MAX_PARTS = 10000; // S3 limit
 
 export async function POST(
   req: NextRequest,
@@ -28,7 +35,14 @@ export async function POST(
     return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
   }
   const { jobId } = await params;
-  let body: { machineId?: string; kind?: string; fileName?: string; contentType?: string };
+  let body: {
+    machineId?: string;
+    kind?: string;
+    fileName?: string;
+    contentType?: string;
+    multipart?: boolean;
+    size?: number;
+  };
   try {
     body = await req.json();
   } catch {
@@ -50,6 +64,14 @@ export async function POST(
     }
 
     const key = `${folder}/${randomUUID()}-${sanitizeFileName(body.fileName)}`;
+
+    if (body.multipart && typeof body.size === "number" && body.size > MIN_PART) {
+      const partSize = Math.max(MIN_PART, Math.ceil(body.size / MAX_PARTS));
+      const partCount = Math.ceil(body.size / partSize);
+      const { uploadId, partUrls } = await createHetznerMultipartUpload(key, body.contentType, partCount);
+      return NextResponse.json({ key, url: `/api/files/${key}`, uploadId, partSize, partUrls });
+    }
+
     const presignedUrl = await generateHetznerPresignedUploadUrl(key, body.contentType);
     return NextResponse.json({ presignedUrl, key, url: `/api/files/${key}` });
   } catch (err) {
diff --git a/lib/render-pipeline/artifact-kinds.ts b/lib/render-pipeline/artifact-kinds.ts
new file mode 100644
index 0000000..3855365
--- /dev/null
+++ b/lib/render-pipeline/artifact-kinds.ts
@@ -0,0 +1,18 @@
+/**
+ * Worker artifact kinds (E20) and the object-storage folder each lands in:
+ * preview → videos/, thumbnail → image/, metadata/log → renders/, highres (the
+ * delivery MOV) → highres/ beside the manually uploaded High Res files.
+ */
+export const ARTIFACT_KIND_FOLDERS: Record<string, string> = {
+  preview: "videos",
+  thumbnail: "image",
+  metadata: "renders",
+  log: "renders",
+  highres: "highres",
+};
+
+/** True for keys artifact-presign could have issued — guards E20b. */
+export function isArtifactKey(key: string): boolean {
+  const folder = key.split("/")[0];
+  return key.includes("/") && !key.includes("..") && Object.values(ARTIFACT_KIND_FOLDERS).includes(folder);
+}
diff --git a/lib/storage.ts b/lib/storage.ts
index 9a92ba9..3082585 100644
--- a/lib/storage.ts
+++ b/lib/storage.ts
@@ -17,6 +17,10 @@ import {
   GetObjectCommand,
   ListObjectsV2Command,
   HeadObjectCommand,
+  CreateMultipartUploadCommand,
+  UploadPartCommand,
+  CompleteMultipartUploadCommand,
+  AbortMultipartUploadCommand,
 } from "@aws-sdk/client-s3";
 import { getSignedUrl } from "@aws-sdk/s3-request-presigner";
 import fs from "fs";
@@ -323,6 +327,65 @@ export async function generateHetznerPresignedUploadUrl(
   return getSignedUrl(client, command, { expiresIn });
 }
 
+/**
+ * Multipart upload with presigned part URLs, for the render worker's large
+ * files. A single PUT from the studio to nbg1 is capped near 0.1 MB/s per
+ * connection (188 ms away, lossy); parts uploaded in parallel scale almost
+ * linearly with the number of connections.
+ *
+ * Part URLs live 6 h: parts queue behind each other, and on a slow uplink the
+ * last ones can start long after the upload began.
+ */
+export async function createHetznerMultipartUpload(
+  key: string,
+  contentType: string,
+  partCount: number,
+  expiresIn: number = 6 * 3600
+): Promise<{ uploadId: string; partUrls: string[] }> {
+  const { client, bucket } = await buildHetznerClient();
+  const created = await client.send(
+    new CreateMultipartUploadCommand({ Bucket: bucket, Key: key, ContentType: contentType })
+  );
+  if (!created.UploadId) throw new Error("Storage did not return an UploadId");
+  const uploadId = created.UploadId;
+  const partUrls = await Promise.all(
+    Array.from({ length: partCount }, (_, i) =>
+      getSignedUrl(
+        client,
+        new UploadPartCommand({ Bucket: bucket, Key: key, UploadId: uploadId, PartNumber: i + 1 }),
+        { expiresIn }
+      )
+    )
+  );
+  return { uploadId, partUrls };
+}
+
+export async function completeHetznerMultipartUpload(
+  key: string,
+  uploadId: string,
+  parts: { partNumber: number; etag: string }[]
+): Promise<void> {
+  const { client, bucket } = await buildHetznerClient();
+  await client.send(
+    new CompleteMultipartUploadCommand({
+      Bucket: bucket,
+      Key: key,
+      UploadId: uploadId,
+      MultipartUpload: {
+        Parts: [...parts]
+          .sort((a, b) => a.partNumber - b.partNumber)
+          .map((p) => ({ PartNumber: p.partNumber, ETag: p.etag })),
+      },
+    })
+  );
+}
+
+/** Frees the parts already stored; otherwise they are billed until expiry. */
+export async function abortHetznerMultipartUpload(key: string, uploadId: string): Promise<void> {
+  const { client, bucket } = await buildHetznerClient();
+  await client.send(new AbortMultipartUploadCommand({ Bucket: bucket, Key: key, UploadId: uploadId }));
+}
+
 /**
  * In-process cache for Hetzner key existence checks.
  * Positive hits (key exists) are cached indefinitely for the process lifetime