diff --git a/install.ps1 b/install.ps1
index 696f4e613a..0797cd3868 100644
--- a/install.ps1
+++ b/install.ps1
@@ -469,6 +469,17 @@ function Install-UnslothStudio {
         param(
             [Parameter(Mandatory = $true)][ScriptBlock]$Command
         )
+        # Installer-pinned index installs (torch) must beat an inherited uv mirror
+        # (#6898): when the command pins an index, clear every uv index env var so
+        # it wins, then restore in finally. Other installs keep the user's mirror.
+        $savedUvIndex = $null
+        if ($Command.ToString() -match '--default-index') {
+            $savedUvIndex = @{}
+            foreach ($n in 'UV_DEFAULT_INDEX', 'UV_INDEX_URL', 'UV_INDEX', 'UV_EXTRA_INDEX_URL') {
+                $savedUvIndex[$n] = [Environment]::GetEnvironmentVariable($n)
+                Remove-Item "Env:$n" -ErrorAction SilentlyContinue
+            }
+        }
         $prevEap = $ErrorActionPreference
         $ErrorActionPreference = "Continue"
         try {
@@ -488,6 +499,7 @@ function Install-UnslothStudio {
             return [int]$LASTEXITCODE
         } finally {
             $ErrorActionPreference = $prevEap
+            if ($savedUvIndex) { foreach ($n in $savedUvIndex.Keys) { if ($null -ne $savedUvIndex[$n]) { Set-Item "Env:$n" $savedUvIndex[$n] } } }
         }
     }
 
@@ -2200,7 +2212,7 @@ exit 0
             # ABI-incompatible torchvision/torchaudio on AMD's per-arch index.
             $visionSpec = if ($ROCmGfxArch -and $torchvisionFloorMap.ContainsKey($ROCmGfxArch)) { $torchvisionFloorMap[$ROCmGfxArch] } else { "torchvision" }
             $audioSpec = if ($ROCmGfxArch -and $torchaudioFloorMap.ContainsKey($ROCmGfxArch)) { $torchaudioFloorMap[$ROCmGfxArch] } else { "torchaudio" }
-            $torchInstallExit = Invoke-InstallCommandRetry -Label "install PyTorch (AMD ROCm)" { uv pip install --python $VenvPython --force-reinstall --index-url $ROCmIndexUrl $torchSpec $visionSpec $audioSpec }
+            $torchInstallExit = Invoke-InstallCommandRetry -Label "install PyTorch (AMD ROCm)" { uv pip install --python $VenvPython --force-reinstall --default-index $ROCmIndexUrl $torchSpec $visionSpec $audioSpec }
             if ($torchInstallExit -ne 0) {
                 # Transient AMD-index failure: fall back to a CPU base so the install
                 # still completes; Studio setup retries ROCm afterwards.
@@ -2209,7 +2221,7 @@ exit 0
                 # torch (e.g. 2.10.0+rocm on gfx110X/gfx90a) that still satisfies the CPU
                 # torch>= range, so without it uv would keep the ROCm build and only swap
                 # the companions -- a mismatched venv the flavor-repair block won't fix.
-                $torchInstallExit = Invoke-InstallCommandRetry -Label "install PyTorch (CPU fallback)" { uv pip install --python $VenvPython --force-reinstall "torch>=2.4,<2.11.0" torchvision torchaudio --index-url $TorchIndexUrl }
+                $torchInstallExit = Invoke-InstallCommandRetry -Label "install PyTorch (CPU fallback)" { uv pip install --python $VenvPython --force-reinstall "torch>=2.4,<2.11.0" torchvision torchaudio --default-index $TorchIndexUrl }
                 if ($torchInstallExit -ne 0) {
                     Write-Host "[ERROR] Failed to install PyTorch (ROCm and CPU base both failed, exit code $torchInstallExit)" -ForegroundColor Red
                     return (Exit-InstallFailure "Failed to install PyTorch (exit code $torchInstallExit)" $torchInstallExit)
@@ -2223,7 +2235,7 @@ exit 0
         } else {
             Write-TauriLog "STEP" "Installing PyTorch"
             substep "installing PyTorch ($TorchIndexUrl)..."
-            $torchInstallExit = Invoke-InstallCommandRetry -Label "install PyTorch" { uv pip install --python $VenvPython "torch>=2.4,<2.11.0" torchvision torchaudio --index-url $TorchIndexUrl }
+            $torchInstallExit = Invoke-InstallCommandRetry -Label "install PyTorch" { uv pip install --python $VenvPython "torch>=2.4,<2.11.0" torchvision torchaudio --default-index $TorchIndexUrl }
             if ($torchInstallExit -ne 0) {
                 Write-Host "[ERROR] Failed to install PyTorch (exit code $torchInstallExit)" -ForegroundColor Red
                 return (Exit-InstallFailure "Failed to install PyTorch (exit code $torchInstallExit)" $torchInstallExit)
@@ -2306,7 +2318,7 @@ exit 0
     # keeps a stale torch==X+cpu against a CUDA index and setup.ps1 then loops on
     # "torch cpu != required cuXXX". Reinstall the right triplet when a GPU build is
     # expected: CUDA from $TorchIndexUrl, ROCm from $ROCmIndexUrl (repo.amd.com gfx*
-    # is a PEP 503 index uv resolves via --index-url, same URL the fresh ROCm install
+    # is a PEP 503 index uv resolves via --default-index, same URL the fresh ROCm install
     # above uses). --no-torch / CPU-only hosts (expected cpu) are no-ops.
     if (-not $SkipTorch) {
         $expectedTorchTag = Get-ExpectedTorchFlavorTag -TorchIndexUrl $TorchIndexUrl -ROCmIndexUrl $ROCmIndexUrl
@@ -2322,7 +2334,7 @@ exit 0
                     $visionSpec = if ($ROCmGfxArch -and $torchvisionFloorMap.ContainsKey($ROCmGfxArch)) { $torchvisionFloorMap[$ROCmGfxArch] } else { "torchvision" }
                     $audioSpec = if ($ROCmGfxArch -and $torchaudioFloorMap.ContainsKey($ROCmGfxArch)) { $torchaudioFloorMap[$ROCmGfxArch] } else { "torchaudio" }
                     substep "PyTorch flavor mismatch (installed $installedTorchTag, need ROCm) -- reinstalling correct build..." "Yellow"
-                    $torchFixExit = Invoke-InstallCommand { uv pip install --python $VenvPython --force-reinstall --index-url $ROCmIndexUrl $rocmSpec $visionSpec $audioSpec }
+                    $torchFixExit = Invoke-InstallCommand { uv pip install --python $VenvPython --force-reinstall --default-index $ROCmIndexUrl $rocmSpec $visionSpec $audioSpec }
                     if ($torchFixExit -ne 0) {
                         Write-Host "[ERROR] Failed to reinstall PyTorch with the correct ROCm build (exit code $torchFixExit)" -ForegroundColor Red
                         return (Exit-InstallFailure "Failed to reinstall PyTorch (ROCm) (exit code $torchFixExit)" $torchFixExit)
@@ -2331,7 +2343,7 @@ exit 0
                 } elseif ($expectedTorchTag -ne 'rocm') {
                     # CUDA: stale +cpu (or wrong cuXXX) against a CUDA index -> reinstall triplet.
                     substep "PyTorch flavor mismatch (installed $installedTorchTag, need $expectedTorchTag) -- reinstalling correct build..." "Yellow"
-                    $torchFixExit = Invoke-InstallCommand { uv pip install --python $VenvPython "torch>=2.4,<2.11.0" torchvision torchaudio --index-url $TorchIndexUrl --reinstall-package torch --reinstall-package torchvision --reinstall-package torchaudio }
+                    $torchFixExit = Invoke-InstallCommand { uv pip install --python $VenvPython "torch>=2.4,<2.11.0" torchvision torchaudio --default-index $TorchIndexUrl --reinstall-package torch --reinstall-package torchvision --reinstall-package torchaudio }
                     if ($torchFixExit -ne 0) {
                         Write-Host "[ERROR] Failed to reinstall PyTorch with the correct CUDA build (exit code $torchFixExit)" -ForegroundColor Red
                         return (Exit-InstallFailure "Failed to reinstall PyTorch ($expectedTorchTag) (exit code $torchFixExit)" $torchFixExit)
diff --git a/install.sh b/install.sh
index 0acc9ec0be..3f4ea92387 100755
--- a/install.sh
+++ b/install.sh
@@ -159,6 +159,12 @@ run_maybe_quiet() {
 run_install_cmd() {
     _label="$1"
     shift
+    # Installer-pinned index installs (torch) must beat an inherited uv mirror
+    # (#6898): when we pass --default-index, neutralize every uv index env var so
+    # the pinned index wins. Other installs keep the user's mirror.
+    case " $* " in
+        *" --default-index "*) set -- env -u UV_DEFAULT_INDEX -u UV_INDEX_URL -u UV_INDEX -u UV_EXTRA_INDEX_URL "$@" ;;
+    esac
     if _is_verbose; then
         "$@" && return 0
         _rc=$?
@@ -2190,9 +2196,9 @@ _expected_torch_flavor_tag() {
     esac
 }
 
-# Whether index ($1) supports a plain --index-url reinstall. pytorch.org cuXXX /
+# Whether index ($1) supports a plain --default-index reinstall. pytorch.org cuXXX /
 # rocmX.Y AND the repo.amd.com gfx* indexes are all PEP 503 simple indexes that uv
-# resolves (torch + every transitive dep) via --index-url -- the same URLs the
+# resolves (torch + every transitive dep) via --default-index -- the same URLs the
 # fresh-install paths above already use -- so a stale wheel is auto-repairable.
 # Unknown/odd-mirror leaves -> no, so we warn rather than risk a wrong reinstall.
 _torch_index_repairable() {
@@ -2744,7 +2750,7 @@ if [ "$_MIGRATED" = true ]; then
                     substep "repairing ROCm torch (overwritten by dependency resolution)..."
                     run_install_cmd_retry "repair ROCm torch" uv pip install --python "$_VENV_PY" \
                         "$TORCH_CONSTRAINT" torchvision torchaudio \
-                        --index-url "$TORCH_INDEX_URL" \
+                        --default-index "$TORCH_INDEX_URL" \
                         --force-reinstall
                 fi
                 ;;
@@ -2870,7 +2876,7 @@ elif [ -n "$TORCH_INDEX_URL" ]; then
                     substep "[WARN] Radeon repo lacks a compatible wheel set for this Python; falling back to ROCm index ($TORCH_INDEX_URL)" "$C_WARN"
                     run_install_cmd_retry "install PyTorch" uv pip install --python "$_VENV_PY" \
                         "$TORCH_CONSTRAINT" torchvision torchaudio \
-                        --index-url "$TORCH_INDEX_URL"
+                        --default-index "$TORCH_INDEX_URL"
                 else
                     substep "installing PyTorch from Radeon repo (${_RADEON_BASE_URL})..."
                     # Pass explicit wheel URLs so the matched trio is
@@ -2893,18 +2899,18 @@ elif [ -n "$TORCH_INDEX_URL" ]; then
                 substep "[WARN] Radeon repo unavailable; falling back to ROCm index ($TORCH_INDEX_URL)" "$C_WARN"
                 run_install_cmd_retry "install PyTorch" uv pip install --python "$_VENV_PY" \
                     "$TORCH_CONSTRAINT" torchvision torchaudio \
-                    --index-url "$TORCH_INDEX_URL"
+                    --default-index "$TORCH_INDEX_URL"
             fi
         else
             substep "[WARN] Radeon GPU detected but could not detect full ROCm version; falling back to ROCm index" "$C_WARN"
             run_install_cmd_retry "install PyTorch" uv pip install --python "$_VENV_PY" \
                 "$TORCH_CONSTRAINT" torchvision torchaudio \
-                --index-url "$TORCH_INDEX_URL"
+                --default-index "$TORCH_INDEX_URL"
         fi
     else
         substep "installing PyTorch ($TORCH_INDEX_URL)..."
         run_install_cmd_retry "install PyTorch" uv pip install --python "$_VENV_PY" "$TORCH_CONSTRAINT" torchvision torchaudio \
-            --index-url "$TORCH_INDEX_URL"
+            --default-index "$TORCH_INDEX_URL"
     fi
     # AMD ROCm: install bitsandbytes (once, after torch, for all ROCm paths).
     # Gate on SKIP_TORCH=false so a user running with --no-torch on a ROCm
@@ -2964,7 +2970,7 @@ elif [ -n "$TORCH_INDEX_URL" ]; then
                     substep "repairing ROCm torch (overwritten by dependency resolution)..."
                     run_install_cmd_retry "repair ROCm torch" uv pip install --python "$_VENV_PY" \
                         "$TORCH_CONSTRAINT" torchvision torchaudio \
-                        --index-url "$TORCH_INDEX_URL" \
+                        --default-index "$TORCH_INDEX_URL" \
                         --force-reinstall
                 fi
                 ;;
@@ -2999,14 +3005,14 @@ if [ "$SKIP_TORCH" = false ] && [ -n "${TORCH_INDEX_URL:-}" ]; then
         _installed_torch_ver=$("$_VENV_PY" -c "import torch; print(torch.__version__)" 2>/dev/null || true)
         _installed_torch_tag=""
         [ -n "$_installed_torch_ver" ] && _installed_torch_tag=$(_torch_flavor_tag "$_installed_torch_ver")
-        # Repair when flavor is wrong AND the index is plain --index-url reinstallable
+        # Repair when flavor is wrong AND the index is plain --default-index reinstallable
         # (cuXXX / rocmX.Y / repo.amd.com gfx*); an unknown mirror leaf -> warn only.
         if [ -n "$_installed_torch_tag" ] && [ "$_installed_torch_tag" != "$_expected_torch_tag" ] \
            && [ "$(_torch_index_repairable "$TORCH_INDEX_URL")" = "yes" ]; then
             substep "PyTorch flavor mismatch (installed $_installed_torch_tag, need $_expected_torch_tag) -- reinstalling correct build..."
             run_install_cmd "reinstall PyTorch ($_expected_torch_tag)" uv pip install --python "$_VENV_PY" \
                 "$TORCH_CONSTRAINT" torchvision torchaudio \
-                --index-url "$TORCH_INDEX_URL" \
+                --default-index "$TORCH_INDEX_URL" \
                 --reinstall-package torch --reinstall-package torchvision --reinstall-package torchaudio
             _installed_torch_ver=$("$_VENV_PY" -c "import torch; print(torch.__version__)" 2>/dev/null || true)
             _installed_torch_tag=""
@@ -3017,7 +3023,7 @@ if [ "$SKIP_TORCH" = false ] && [ -n "${TORCH_INDEX_URL:-}" ]; then
             substep "[WARN] PyTorch is CPU-only but a $_expected_torch_tag GPU build was expected for this machine." "$C_WARN"
             substep "[WARN] Training and GPU inference will run on CPU until this is fixed." "$C_WARN"
             substep "[WARN] Re-run this installer, or reinstall the GPU build manually:" "$C_WARN"
-            substep "[WARN]   uv pip install --python \"$_VENV_PY\" \"$TORCH_CONSTRAINT\" torchvision torchaudio --index-url $TORCH_INDEX_URL --reinstall-package torch --reinstall-package torchvision --reinstall-package torchaudio" "$C_WARN"
+            substep "[WARN]   uv pip install --python \"$_VENV_PY\" \"$TORCH_CONSTRAINT\" torchvision torchaudio --default-index $TORCH_INDEX_URL --reinstall-package torch --reinstall-package torchvision --reinstall-package torchaudio" "$C_WARN"
         fi
     fi
 fi
diff --git a/studio/setup.ps1 b/studio/setup.ps1
index 07dcb17335..db01a1ecad 100644
--- a/studio/setup.ps1
+++ b/studio/setup.ps1
@@ -2621,7 +2621,18 @@ function Fast-Install {
     param([Parameter(ValueFromRemainingArguments=$true)]$Args_)
     if ($UseUv) {
         $VenvPy = (Get-Command python).Source
-        $result = & uv pip install --python $VenvPy @Args_ 2>&1
+        # An explicit --index-url must win. Inherited uv index env vars otherwise
+        # override it and pull CPU torch over the CUDA/ROCm build (#6898), so drop
+        # them only for index-pinned installs; mirrors still apply elsewhere.
+        $saved = @{}
+        if (@($Args_) -contains '--index-url') {
+            foreach ($n in 'UV_DEFAULT_INDEX', 'UV_INDEX_URL', 'UV_INDEX', 'UV_EXTRA_INDEX_URL') {
+                $saved[$n] = [Environment]::GetEnvironmentVariable($n)
+                Remove-Item "Env:$n" -ErrorAction SilentlyContinue
+            }
+        }
+        try { $result = & uv pip install --python $VenvPy @Args_ 2>&1 }
+        finally { foreach ($n in $saved.Keys) { if ($null -ne $saved[$n]) { Set-Item "Env:$n" $saved[$n] } } }
         if ($LASTEXITCODE -eq 0) { return }
     }
     & python -m pip install @Args_ 2>&1
diff --git a/tests/python/test_tokenizers_and_torch_constraint.py b/tests/python/test_tokenizers_and_torch_constraint.py
index 7390d7be9b..4322f0c7d6 100644
--- a/tests/python/test_tokenizers_and_torch_constraint.py
+++ b/tests/python/test_tokenizers_and_torch_constraint.py
@@ -14,6 +14,7 @@ _TESTS_DIR = pathlib.Path(__file__).resolve().parent.parent  # tests/
 _REPO_ROOT = _TESTS_DIR.parent  # unsloth/
 _INSTALL_SH = _REPO_ROOT / "install.sh"
 _INSTALL_PS1 = _REPO_ROOT / "install.ps1"
+_SETUP_PS1 = _REPO_ROOT / "studio" / "setup.ps1"
 _NO_TORCH_RT = _REPO_ROOT / "studio" / "backend" / "requirements" / "no-torch-runtime.txt"
 
 
@@ -109,6 +110,56 @@ class TestStructuralInstallPs1Unchanged:
         assert '"torch>=2.4,<2.11.0"' in self._ps1
 
 
+class TestInstallPs1UvDefaultIndex:
+    """Installer-managed torch indexes must override inherited uv defaults."""
+
+    _ps1 = _read(_INSTALL_PS1)
+
+    def test_torch_installs_use_default_index(self):
+        assert "--default-index $TorchIndexUrl" in self._ps1
+        assert "--default-index $ROCmIndexUrl" in self._ps1
+
+    def test_torch_installs_do_not_use_deprecated_index_url(self):
+        assert "--index-url $TorchIndexUrl" not in self._ps1
+        assert "--index-url $ROCmIndexUrl" not in self._ps1
+
+    def test_torch_installs_neutralize_all_uv_index_env_vars(self):
+        # Extra-index vars outrank --default-index, so pinned installs must clear them.
+        for var in ("UV_DEFAULT_INDEX", "UV_INDEX_URL", "UV_INDEX", "UV_EXTRA_INDEX_URL"):
+            assert var in self._ps1
+        assert 'Remove-Item "Env:$n"' in self._ps1
+
+
+class TestSetupPs1FastInstallIndex:
+    """setup.ps1 Fast-Install must neutralize inherited uv indexes when pinning."""
+
+    _ps1 = _read(_SETUP_PS1)
+
+    def test_fast_install_clears_all_uv_index_env_vars(self):
+        for var in ("UV_DEFAULT_INDEX", "UV_INDEX_URL", "UV_INDEX", "UV_EXTRA_INDEX_URL"):
+            assert var in self._ps1
+        # Must truly remove the vars (child sees no value), not set them empty.
+        assert 'Remove-Item "Env:$n"' in self._ps1
+
+
+class TestInstallShUvDefaultIndex:
+    """Linux/Mac installer torch indexes must override inherited uv defaults."""
+
+    _sh = _read(_INSTALL_SH)
+
+    def test_torch_installs_use_default_index(self):
+        assert '--default-index "$TORCH_INDEX_URL"' in self._sh
+
+    def test_torch_installs_do_not_use_deprecated_index_url(self):
+        assert '--index-url "$TORCH_INDEX_URL"' not in self._sh
+
+    def test_torch_installs_neutralize_all_uv_index_env_vars(self):
+        # --default-index installs run with all uv index env vars unset via `env -u`.
+        assert (
+            "env -u UV_DEFAULT_INDEX -u UV_INDEX_URL -u UV_INDEX -u UV_EXTRA_INDEX_URL" in self._sh
+        )
+
+
 # Group 2 -- Shell snippet tests (bash subprocess, mocked python)
 class TestTorchConstraintShell:
     """Test the TORCH_CONSTRAINT block via bash with mocked python minor versions."""
diff --git a/tests/sh/test_mac_intel_compat.sh b/tests/sh/test_mac_intel_compat.sh
index 3c3bbfaa5f..8a0ff4b641 100644
--- a/tests/sh/test_mac_intel_compat.sh
+++ b/tests/sh/test_mac_intel_compat.sh
@@ -312,7 +312,7 @@ if [ "$SKIP_TORCH" = true ]; then
 else
     echo "==> Installing PyTorch ($TORCH_INDEX_URL)..."
     uv pip install --python "$_VENV_PY" "torch>=2.4,<2.11.0" torchvision torchaudio \
-        --index-url "$TORCH_INDEX_URL"
+        --default-index "$TORCH_INDEX_URL"
 fi
 TORCH_EOF