upgrade CUDA backend from cu126 to cu128 and fix GPU settings UI

Upgrade CUDA toolkit from 12.6 (cu126) to 12.8 (cu128) for proper
RTX 50-series (Blackwell) GPU support. Users with RTX 5070/5080/5090
were reporting CUDA detection failures with cu126.

Also fix the GPU Acceleration settings panel where the 'Switch to CPU
Backend' button was unreachable — it was inside a conditional block
that required !isCurrentlyCuda, making it impossible to switch back
to CPU once running on CUDA.

Closes #315

.github/workflows/release.yml

@@ -191,10 +191,10 @@ jobs:
           pip install --no-deps chatterbox-tts
           pip install --no-deps hume-tada
 
-      - name: Install PyTorch with CUDA 12.6
+      - name: Install PyTorch with CUDA 12.8
         run: |
-          pip install torch --index-url https://download.pytorch.org/whl/cu126 --force-reinstall --no-deps
-          pip install torchaudio --index-url https://download.pytorch.org/whl/cu126 --force-reinstall --no-deps
+          pip install torch --index-url https://download.pytorch.org/whl/cu128 --force-reinstall --no-deps
+          pip install torchaudio --index-url https://download.pytorch.org/whl/cu128 --force-reinstall --no-deps
 
       - name: Verify CUDA support in torch
         run: |
@@ -211,8 +211,8 @@ jobs:
           python scripts/package_cuda.py \
             backend/dist/voicebox-server-cuda/ \
             --output release-assets/ \
-            --cuda-libs-version cu126-v1 \
-            --torch-compat ">=2.6.0,<2.11.0"
+            --cuda-libs-version cu128-v1 \
+            --torch-compat ">=2.7.0,<2.11.0"
 
       - name: Upload archives to GitHub Release
         if: startsWith(github.ref, 'refs/tags/')
@@ -221,8 +221,8 @@ jobs:
           files: |
             release-assets/voicebox-server-cuda.tar.gz
             release-assets/voicebox-server-cuda.tar.gz.sha256
-            release-assets/cuda-libs-cu126-v1.tar.gz
-            release-assets/cuda-libs-cu126-v1.tar.gz.sha256
+            release-assets/cuda-libs-cu128-v1.tar.gz
+            release-assets/cuda-libs-cu128-v1.tar.gz.sha256
             release-assets/cuda-libs.json
           draft: true
         env:

app/src/components/ServerSettings/GpuAcceleration.tsx

@@ -243,7 +243,40 @@ export function GpuAcceleration() {
 
         {/* Native GPU detected - no CUDA download needed */}
 
-        {/* CUDA download section - only show when no GPU is active (native or CUDA) */}
+        {/* Currently running CUDA - show switch back to CPU */}
+        {isCurrentlyCuda && platform.metadata.isTauri && (
+          <>
+            {restartPhase !== 'idle' ? (
+              <div className="flex items-center gap-2 p-3 rounded-lg bg-primary/5 border">
+                <Loader2 className="h-4 w-4 animate-spin" />
+                <span className="text-sm">
+                  {restartPhase === 'stopping' && 'Stopping server...'}
+                  {restartPhase === 'waiting' && 'Restarting server...'}
+                  {restartPhase === 'ready' && 'Server restarted successfully!'}
+                </span>
+              </div>
+            ) : (
+              <div className="space-y-3">
+                <p className="text-sm text-muted-foreground">
+                  Running with CUDA GPU acceleration. Switch back to CPU if needed (you can
+                  re-download later).
+                </p>
+                <Button onClick={handleSwitchToCpu} variant="outline" className="w-full" size="sm">
+                  <RotateCw className="h-4 w-4 mr-2" />
+                  Switch to CPU Backend
+                </Button>
+              </div>
+            )}
+            {error && (
+              <div className="flex items-center gap-2 text-sm text-destructive">
+                <AlertCircle className="h-4 w-4 shrink-0" />
+                <span>{error}</span>
+              </div>
+            )}
+          </>
+        )}
+
+        {/* CUDA download/manage section - show when no native GPU and not currently running CUDA */}
         {!hasNativeGpu && !isCurrentlyCuda && (
           <>
             {/* Download progress (manual download or auto-update) */}
@@ -315,7 +348,7 @@ export function GpuAcceleration() {
                 )}
 
                 {/* Downloaded but not active - show switch button */}
-                {cudaAvailable && !isCurrentlyCuda && platform.metadata.isTauri && (
+                {cudaAvailable && platform.metadata.isTauri && (
                   <div className="space-y-3">
                     <p className="text-sm text-muted-foreground">
                       CUDA backend is downloaded and ready. Restart the server to enable GPU
@@ -328,27 +361,8 @@ export function GpuAcceleration() {
                   </div>
                 )}
 
-                {/* Currently active - show switch back to CPU */}
-                {isCurrentlyCuda && platform.metadata.isTauri && (
-                  <div className="space-y-3">
-                    <p className="text-sm text-muted-foreground">
-                      Running with CUDA GPU acceleration. Switch back to CPU if needed (you can
-                      re-download later).
-                    </p>
-                    <Button
-                      onClick={handleSwitchToCpu}
-                      variant="outline"
-                      className="w-full"
-                      size="sm"
-                    >
-                      <RotateCw className="h-4 w-4 mr-2" />
-                      Switch to CPU Backend
-                    </Button>
-                  </div>
-                )}
-
                 {/* Delete option when downloaded (and not active) */}
-                {cudaAvailable && !isCurrentlyCuda && (
+                {cudaAvailable && (
                   <Button
                     onClick={handleDelete}
                     variant="ghost"

backend/build_binary.py

@@ -370,7 +370,7 @@ def build_server(cuda=False):
                     "torchvision",
                     "torchaudio",
                     "--index-url",
-                    "https://download.pytorch.org/whl/cu126",
+                    "https://download.pytorch.org/whl/cu128",
                     "--force-reinstall",
                     "-q",
                 ],

backend/requirements.txt

@@ -8,7 +8,7 @@ sqlalchemy>=2.0.0
 alembic>=1.13.0
 
 # ML models
-torch>=2.1.0
+torch>=2.7.0
 transformers>=4.36.0,<=4.57.6
 accelerate>=0.26.0
 huggingface_hub>=0.20.0

backend/services/cuda.py

@@ -32,7 +32,7 @@ PROGRESS_KEY = "cuda-backend"
 
 # The current expected CUDA libs version.  Bump this when we change the
 # CUDA toolkit version or torch's CUDA dependency changes (e.g. cu126 -> cu128).
-CUDA_LIBS_VERSION = "cu126-v1"
+CUDA_LIBS_VERSION = "cu128-v1"
 
 
 def get_backends_dir() -> Path:

docs/content/docs/developer/building.mdx

@@ -159,11 +159,11 @@ Tauri looks for `voicebox-server-${PLATFORM}` in `src-tauri/binaries/` and bundl
 
 The `build-cuda-windows` job runs separately:
 
-1. Install PyTorch with CUDA 12.6
+1. Install PyTorch with CUDA 12.8
 2. Build with `build_binary.py --cuda` (produces `--onedir` output)
 3. Package with `scripts/package_cuda.py` into two archives:
    - `voicebox-server-cuda.tar.gz` — server core (~945 MB)
-   - `cuda-libs-cu126-v1.tar.gz` — NVIDIA runtime libraries (~1.7 GB, cached independently)
+   - `cuda-libs-cu128-v1.tar.gz` — NVIDIA runtime libraries (~1.7 GB, cached independently)
 4. Upload archives as release artifacts
 
 This binary is downloaded on-demand by users who enable CUDA in settings. The CUDA libs archive is only re-downloaded when the CUDA toolkit version changes, not on every app update.

justfile

@@ -72,7 +72,7 @@ setup-python:
     $hasNvidia = $null -ne (Get-WmiObject Win32_VideoController | Where-Object { $_.Name -match 'NVIDIA' })
     if ($hasNvidia) { \
         Write-Host "NVIDIA GPU detected — installing PyTorch with CUDA support..."; \
-        & "{{ pip }}" install torch torchvision torchaudio --index-url https://download.pytorch.org/whl/cu126; \
+        & "{{ pip }}" install torch torchvision torchaudio --index-url https://download.pytorch.org/whl/cu128; \
     }
     & "{{ pip }}" install -r {{ backend_dir }}/requirements.txt
     & "{{ pip }}" install --no-deps chatterbox-tts

scripts/package_cuda.py

@@ -3,13 +3,13 @@ Package the PyInstaller --onedir CUDA build into two archives.
 
 Takes the PyInstaller --onedir output directory and splits it into:
   1. voicebox-server-cuda.tar.gz  — server core (exe + non-NVIDIA deps)
-  2. cuda-libs-cu126.tar.gz       — NVIDIA runtime libraries only
+  2. cuda-libs-cu128.tar.gz       — NVIDIA runtime libraries only
   3. cuda-libs.json                — version manifest for the CUDA libs
 
 Usage:
     python scripts/package_cuda.py backend/dist/voicebox-server-cuda/
     python scripts/package_cuda.py backend/dist/voicebox-server-cuda/ --output release-assets/
-    python scripts/package_cuda.py backend/dist/voicebox-server-cuda/ --cuda-libs-version cu126-v1
+    python scripts/package_cuda.py backend/dist/voicebox-server-cuda/ --cuda-libs-version cu128-v1
 """
 
 import argparse
@@ -208,13 +208,13 @@ def main():
     parser.add_argument(
         "--cuda-libs-version",
         type=str,
-        default="cu126-v1",
-        help="Version string for the CUDA libs archive (default: cu126-v1)",
+        default="cu128-v1",
+        help="Version string for the CUDA libs archive (default: cu128-v1)",
     )
     parser.add_argument(
         "--torch-compat",
         type=str,
-        default=">=2.6.0,<2.11.0",
+        default=">=2.7.0,<2.11.0",
         help="Torch version compatibility range (default: >=2.6.0,<2.11.0)",
     )
     args = parser.parse_args()