diff --git a/backend/smb/filepool.go b/backend/smb/filepool.go
new file mode 100644
index 000000000..ace4d99bd
--- /dev/null
+++ b/backend/smb/filepool.go
@@ -0,0 +1,91 @@
+package smb
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/cloudsoda/go-smb2"
+	"golang.org/x/sync/errgroup"
+)
+
+type smbChunkWriterFile struct {
+	*smb2.File
+	c *conn
+}
+
+func (w *smbChunkWriter) getFile(ctx context.Context) (f *smbChunkWriterFile, err error) {
+	w.poolMu.Lock()
+	if len(w.pool) > 0 {
+		f = w.pool[0]
+		w.pool = w.pool[1:]
+	}
+	w.poolMu.Unlock()
+
+	if f != nil {
+		return f, nil
+	}
+
+	w.f.addSession() // Show session in use
+
+	c, err := w.f.getConnection(ctx, w.share)
+	if err != nil {
+		w.f.removeSession()
+		return nil, err
+	}
+
+	fl, err := c.smbShare.OpenFile(w.filename, os.O_WRONLY, 0o644)
+	if err != nil {
+		w.f.putConnection(&c, err)
+		w.f.removeSession()
+		return nil, fmt.Errorf("failed to open: %w", err)
+	}
+
+	return &smbChunkWriterFile{File: fl, c: c}, nil
+}
+
+func (w *smbChunkWriter) putFile(pf **smbChunkWriterFile, err error) {
+	if pf == nil {
+		return
+	}
+	f := *pf
+	if f == nil {
+		return
+	}
+	*pf = nil
+
+	if err != nil {
+		_ = f.Close()
+		w.f.putConnection(&f.c, err)
+		w.f.removeSession()
+		return
+	}
+
+	w.poolMu.Lock()
+	w.pool = append(w.pool, f)
+	w.poolMu.Unlock()
+}
+
+func (w *smbChunkWriter) drainPool(ctx context.Context) (err error) {
+	w.poolMu.Lock()
+	defer w.poolMu.Unlock()
+
+	if len(w.pool) == 0 {
+		return nil
+	}
+
+	g, _ := errgroup.WithContext(ctx)
+	for i, f := range w.pool {
+		g.Go(func() error {
+			err := f.Close()
+			w.f.putConnection(&f.c, err)
+			w.f.removeSession()
+			w.pool[i] = nil
+			return err
+		})
+	}
+	err = g.Wait()
+	w.pool = nil
+
+	return err
+}
diff --git a/backend/smb/smb.go b/backend/smb/smb.go
index c6911fb76..5eb04a37b 100644
--- a/backend/smb/smb.go
+++ b/backend/smb/smb.go
@@ -3,6 +3,7 @@ package smb
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -20,14 +21,18 @@ import (
 	"github.com/rclone/rclone/lib/bucket"
 	"github.com/rclone/rclone/lib/encoder"
 	"github.com/rclone/rclone/lib/env"
+	"github.com/rclone/rclone/lib/multipart"
 	"github.com/rclone/rclone/lib/pacer"
 	"github.com/rclone/rclone/lib/readers"
 )
 
 const (
-	minSleep      = 10 * time.Millisecond
-	maxSleep      = 2 * time.Second
-	decayConstant = 2 // bigger for slower decay, exponential
+	minSleep                 = 10 * time.Millisecond
+	maxSleep                 = 2 * time.Second
+	decayConstant            = 2 // bigger for slower decay, exponential
+	defaultChunkSize         = 5 * fs.Mebi
+	defaultUploadCutoff      = 200 * fs.Mebi
+	defaultUploadConcurrency = 4
 )
 
 var (
@@ -124,22 +129,54 @@ Set to 0 to keep connections indefinitely.
 				encoder.EncodeRightPeriod |
 				//
 				encoder.EncodeInvalidUtf8,
+		}, {
+			Name: "upload_cutoff",
+			Help: `Cutoff for switching to chunked upload.
+
+Files above this size will be uploaded in chunks of "--smb-chunk-size".`,
+			Default:  defaultUploadCutoff,
+			Advanced: true,
+		}, {
+			Name: "chunk_size",
+			Help: `Upload chunk size.
+
+When uploading large files, chunk the file into this size.
+
+Must fit in memory. These chunks are buffered in memory and there
+might a maximum of "--transfers" chunks in progress at once.`,
+			Default:  defaultChunkSize,
+			Advanced: true,
+		}, {
+			Name: "upload_concurrency",
+			Help: `Concurrency for multipart uploads.
+
+This is the number of chunks of the same file that are uploaded
+concurrently.
+
+Note that chunks are stored in memory and there may be up to
+"--transfers" * "--smb-upload-concurrency" chunks stored at once
+in memory.`,
+			Default:  defaultUploadConcurrency,
+			Advanced: true,
 		},
 		}})
 }
 
 // Options defines the configuration for this backend
 type Options struct {
-	Host            string      `config:"host"`
-	Port            string      `config:"port"`
-	User            string      `config:"user"`
-	Pass            string      `config:"pass"`
-	Domain          string      `config:"domain"`
-	SPN             string      `config:"spn"`
-	UseKerberos     bool        `config:"use_kerberos"`
-	HideSpecial     bool        `config:"hide_special_share"`
-	CaseInsensitive bool        `config:"case_insensitive"`
-	IdleTimeout     fs.Duration `config:"idle_timeout"`
+	Host              string        `config:"host"`
+	Port              string        `config:"port"`
+	User              string        `config:"user"`
+	Pass              string        `config:"pass"`
+	Domain            string        `config:"domain"`
+	SPN               string        `config:"spn"`
+	UseKerberos       bool          `config:"use_kerberos"`
+	HideSpecial       bool          `config:"hide_special_share"`
+	CaseInsensitive   bool          `config:"case_insensitive"`
+	IdleTimeout       fs.Duration   `config:"idle_timeout"`
+	UploadCutoff      fs.SizeSuffix `config:"upload_cutoff"`
+	ChunkSize         fs.SizeSuffix `config:"chunk_size"`
+	UploadConcurrency int           `config:"upload_concurrency"`
 
 	Enc encoder.MultiEncoder `config:"encoding"`
 }
@@ -176,6 +213,19 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 		return nil, err
 	}
 
+	if opt.UploadCutoff < opt.ChunkSize {
+		opt.UploadCutoff = opt.ChunkSize
+		fs.Infof(nil, "smb: raising upload cutoff to chunk size: %v", opt.UploadCutoff)
+	}
+	err = checkUploadChunkSize(opt.ChunkSize)
+	if err != nil {
+		return nil, fmt.Errorf("smb: chunk size: %w", err)
+	}
+	err = checkUploadCutoff(opt, opt.UploadCutoff)
+	if err != nil {
+		return nil, fmt.Errorf("smb: upload cutoff: %w", err)
+	}
+
 	root = strings.Trim(root, "/")
 
 	f := &Fs{
@@ -488,25 +538,70 @@ func (f *Fs) About(ctx context.Context) (_ *fs.Usage, err error) {
 	return usage, nil
 }
 
-// OpenWriterAt opens with a handle for random access writes
+func checkUploadChunkSize(cs fs.SizeSuffix) error {
+	const minChunkSize = fs.SizeSuffixBase
+	if cs < minChunkSize {
+		return fmt.Errorf("%s is less than %s", cs, minChunkSize)
+	}
+	return nil
+}
+
+func (f *Fs) setUploadChunkSize(cs fs.SizeSuffix) (old fs.SizeSuffix, err error) {
+	err = checkUploadChunkSize(cs)
+	if err == nil {
+		old, f.opt.ChunkSize = f.opt.ChunkSize, cs
+	}
+	return
+}
+
+func checkUploadCutoff(opt *Options, cs fs.SizeSuffix) error {
+	if cs < opt.ChunkSize {
+		return fmt.Errorf("%v is less than chunk size %v", cs, opt.ChunkSize)
+	}
+	return nil
+}
+
+func (f *Fs) setUploadCutoff(cs fs.SizeSuffix) (old fs.SizeSuffix, err error) {
+	err = checkUploadCutoff(&f.opt, cs)
+	if err == nil {
+		old, f.opt.UploadCutoff = f.opt.UploadCutoff, cs
+	}
+	return
+}
+
+// Implements the fs.ChunkWriter interface
+type smbChunkWriter struct {
+	chunkSize int64
+	f         *Fs
+	o         *Object
+	src       fs.ObjectInfo
+	share     string
+	filename  string
+
+	closed  bool
+	closeMu sync.Mutex
+	wg      sync.WaitGroup
+	poolMu  sync.Mutex
+	pool    []*smbChunkWriterFile
+}
+
+// OpenChunkWriter returns the chunk size and a ChunkWriter
 //
-// Pass in the remote desired and the size if known.
-//
-// It truncates any existing object
-func (f *Fs) OpenWriterAt(ctx context.Context, remote string, size int64) (fs.WriterAtCloser, error) {
-	var err error
+// Pass in the remote and the src object
+// You can also use options to hint at the desired chunk size
+func (f *Fs) OpenChunkWriter(ctx context.Context, remote string, src fs.ObjectInfo, options ...fs.OpenOption) (info fs.ChunkWriterInfo, writer fs.ChunkWriter, err error) {
 	o := &Object{
 		fs:     f,
 		remote: remote,
 	}
 	share, filename := o.split()
 	if share == "" || filename == "" {
-		return nil, fs.ErrorIsDir
+		return info, nil, fs.ErrorIsDir
 	}
 
 	err = o.fs.ensureDirectory(ctx, share, filename)
 	if err != nil {
-		return nil, fmt.Errorf("failed to make parent directories: %w", err)
+		return info, nil, fmt.Errorf("failed to make parent directories: %w", err)
 	}
 
 	filename = o.fs.toSambaPath(filename)
@@ -516,15 +611,132 @@ func (f *Fs) OpenWriterAt(ctx context.Context, remote string, size int64) (fs.Wr
 
 	cn, err := o.fs.getConnection(ctx, share)
 	if err != nil {
-		return nil, err
+		return info, nil, err
 	}
+	defer o.fs.putConnection(&cn, err)
 
+	// create the file or truncate it
 	fl, err := cn.smbShare.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
 	if err != nil {
-		return nil, fmt.Errorf("failed to open: %w", err)
+		return info, nil, fmt.Errorf("failed to open: %w", err)
+	}
+	defer func() {
+		cErr := fl.Close()
+		if cErr != nil {
+			err = errors.Join(err, fmt.Errorf("failed to close: %w", cErr))
+		}
+	}()
+
+	// preallocate the file to the correct size if possible
+	if src.Size() > 0 {
+		err = fl.Truncate(src.Size())
+		if err != nil {
+			return info, nil, fmt.Errorf("failed to truncate: %w", err)
+		}
 	}
 
-	return fl, nil
+	chunkSize := int64(f.opt.ChunkSize)
+	for _, opt := range options {
+		if chunkOption, ok := opt.(*fs.ChunkOption); ok {
+			chunkSize = chunkOption.ChunkSize
+		}
+	}
+
+	chunkWriter := &smbChunkWriter{
+		chunkSize: chunkSize,
+		f:         f,
+		o:         o,
+		src:       src,
+		share:     share,
+		filename:  filename,
+	}
+
+	info = fs.ChunkWriterInfo{
+		ChunkSize:   chunkSize,
+		Concurrency: f.opt.UploadConcurrency,
+	}
+
+	fs.Debugf(o, "open chunk writer: started multipart upload")
+
+	return info, chunkWriter, nil
+}
+
+// WriteChunk will write chunk number with reader bytes, where chunk number >= 0
+func (w *smbChunkWriter) WriteChunk(ctx context.Context, chunkNumber int, reader io.ReadSeeker) (n int64, err error) {
+	if w.closed {
+		return 0, errors.New("multipart upload already closed")
+	}
+
+	w.wg.Add(1)
+	defer w.wg.Done()
+
+	fl, err := w.getFile(ctx)
+	if err != nil {
+		return 0, fmt.Errorf("failed to open: %w", err)
+	}
+	defer w.putFile(&fl, err)
+
+	_, err = fl.Seek(int64(chunkNumber)*w.chunkSize, io.SeekStart)
+	if err != nil {
+		return 0, fmt.Errorf("failed to seek: %w", err)
+	}
+
+	n, err = io.CopyN(fl, reader, w.chunkSize)
+	if err != nil && !errors.Is(err, io.EOF) {
+		return n, fmt.Errorf("failed to copy: %w", err)
+	}
+
+	fs.Debugf(w.o, "multipart upload wrote chunk %d with %d bytes", chunkNumber+1, n)
+
+	return n, nil
+}
+
+// Close and finalise the multipart upload
+func (w *smbChunkWriter) Close(ctx context.Context) (err error) {
+	w.closeMu.Lock()
+	defer w.closeMu.Unlock()
+
+	if w.closed {
+		return nil
+	}
+	w.closed = true
+
+	w.wg.Wait() // wait for all pending writes to finish
+
+	var errs []error
+	if err := w.drainPool(ctx); err != nil {
+		errs = append(errs, fmt.Errorf("failed to drain file pool: %w", err))
+	}
+	if err := w.o.SetModTime(ctx, w.src.ModTime(ctx)); err != nil {
+		errs = append(errs, fmt.Errorf("failed to set modtime: %w", err))
+	}
+
+	if len(errs) > 0 {
+		return errors.Join(errs...)
+	}
+
+	fs.Debug(w.o, "multipart upload finished")
+
+	return nil
+}
+
+// Abort the multipart upload.
+func (w *smbChunkWriter) Abort(ctx context.Context) (err error) {
+	fs.Debugf(w.o, "aborting multipart upload")
+
+	err = w.Close(ctx)
+	if err != nil {
+		fs.Errorf(w.o, "failed to close before aborting: %v", err)
+	}
+
+	err = w.o.Remove(ctx)
+	if err != nil {
+		fs.Errorf(w.o, "failed to remove file after aborting: %v", err)
+	}
+
+	fs.Debug(w.o, "multipart upload aborted")
+
+	return nil
 }
 
 // Shutdown the backend, closing any background tasks and any
@@ -676,8 +888,27 @@ func (o *Object) Open(ctx context.Context, options ...fs.OpenOption) (in io.Read
 	return in, nil
 }
 
+func (o *Object) uploadMultipart(ctx context.Context, src fs.ObjectInfo, in io.Reader, options ...fs.OpenOption) (err error) {
+	cw, err := multipart.UploadMultipart(ctx, src, in, multipart.UploadMultipartOptions{
+		Open:        o.fs,
+		OpenOptions: options,
+	})
+	if err != nil {
+		return err
+	}
+
+	o.statResult = cw.(*smbChunkWriter).o.statResult
+
+	return nil
+}
+
 // Update the Object from in with modTime and size
 func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) (err error) {
+	size := src.Size()
+	if size < 0 || size >= int64(o.fs.opt.UploadCutoff) {
+		return o.uploadMultipart(ctx, src, in, options...)
+	}
+
 	share, filename := o.split()
 	if share == "" || filename == "" {
 		return fs.ErrorIsDir
diff --git a/backend/smb/smb_test.go b/backend/smb/smb_test.go
index f22bdb7f9..69f2bfa71 100644
--- a/backend/smb/smb_test.go
+++ b/backend/smb/smb_test.go
@@ -1,11 +1,11 @@
 // Test smb filesystem interface
-package smb_test
+package smb
 
 import (
 	"path/filepath"
 	"testing"
 
-	"github.com/rclone/rclone/backend/smb"
+	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fstest/fstests"
 )
 
@@ -13,7 +13,7 @@ import (
 func TestIntegration(t *testing.T) {
 	fstests.Run(t, &fstests.Opt{
 		RemoteName: "TestSMB:rclone",
-		NilObject:  (*smb.Object)(nil),
+		NilObject:  (*Object)(nil),
 	})
 }
 
@@ -23,6 +23,19 @@ func TestIntegration2(t *testing.T) {
 	t.Setenv("KRB5CCNAME", filepath.Join(krb5Dir, "ccache"))
 	fstests.Run(t, &fstests.Opt{
 		RemoteName: "TestSMBKerberos:rclone",
-		NilObject:  (*smb.Object)(nil),
+		NilObject:  (*Object)(nil),
 	})
 }
+
+func (f *Fs) SetUploadChunkSize(cs fs.SizeSuffix) (fs.SizeSuffix, error) {
+	return f.setUploadChunkSize(cs)
+}
+
+func (f *Fs) SetUploadCutoff(cs fs.SizeSuffix) (fs.SizeSuffix, error) {
+	return f.setUploadCutoff(cs)
+}
+
+var (
+	_ fstests.SetUploadChunkSizer = (*Fs)(nil)
+	_ fstests.SetUploadCutoffer   = (*Fs)(nil)
+)
diff --git a/docs/content/docs.md b/docs/content/docs.md
index 17c909fea..bebc9eb4d 100644
--- a/docs/content/docs.md
+++ b/docs/content/docs.md
@@ -1751,7 +1751,7 @@ multiples of 16k performed much better than other values.
 ### --multi-thread-chunk-size=SizeSuffix ###
 
 Normally the chunk size for multi thread transfers is set by the backend.
-However some backends such as `local` and `smb` (which implement `OpenWriterAt`
+However some backends such as `local` and `pcloud` (which implement `OpenWriterAt`
 but not `OpenChunkWriter`) don't have a natural chunk size.
 
 In this case the value of this option is used (default 64Mi).