Remove preview label from --torch-backend (#14119)

This is now used in enough places that I'm comfortable committing to
maintaining it under our versioning policy.

Closes #14091.

crates/uv/src/commands/pip/compile.rs

@@ -388,20 +388,18 @@ pub(crate) async fn pip_compile(
     }
 
     // Determine the PyTorch backend.
-    let torch_backend = torch_backend.map(|mode| {
-        if preview.is_disabled() {
-            warn_user!("The `--torch-backend` setting is experimental and may change without warning. Pass `--preview` to disable this warning.");
-        }
-
-        TorchStrategy::from_mode(
-            mode,
-            python_platform
-                .map(TargetTriple::platform)
-                .as_ref()
-                .unwrap_or(interpreter.platform())
-                .os(),
-        )
-    }).transpose()?;
+    let torch_backend = torch_backend
+        .map(|mode| {
+            TorchStrategy::from_mode(
+                mode,
+                python_platform
+                    .map(TargetTriple::platform)
+                    .as_ref()
+                    .unwrap_or(interpreter.platform())
+                    .os(),
+            )
+        })
+        .transpose()?;
 
     // Initialize the registry client.
     let client = RegistryClientBuilder::try_from(client_builder)?

crates/uv/src/commands/pip/install.rs

@@ -344,20 +344,18 @@ pub(crate) async fn pip_install(
     }
 
     // Determine the PyTorch backend.
-    let torch_backend = torch_backend.map(|mode| {
-        if preview.is_disabled() {
-            warn_user!("The `--torch-backend` setting is experimental and may change without warning. Pass `--preview` to disable this warning.");
-        }
-
-        TorchStrategy::from_mode(
-            mode,
-            python_platform
-                .map(TargetTriple::platform)
-                .as_ref()
-                .unwrap_or(interpreter.platform())
-                .os(),
-        )
-    }).transpose()?;
+    let torch_backend = torch_backend
+        .map(|mode| {
+            TorchStrategy::from_mode(
+                mode,
+                python_platform
+                    .map(TargetTriple::platform)
+                    .as_ref()
+                    .unwrap_or(interpreter.platform())
+                    .os(),
+            )
+        })
+        .transpose()?;
 
     // Initialize the registry client.
     let client = RegistryClientBuilder::try_from(client_builder)?

crates/uv/src/commands/pip/sync.rs

@@ -277,20 +277,18 @@ pub(crate) async fn pip_sync(
     }
 
     // Determine the PyTorch backend.
-    let torch_backend = torch_backend.map(|mode| {
-        if preview.is_disabled() {
-            warn_user!("The `--torch-backend` setting is experimental and may change without warning. Pass `--preview` to disable this warning.");
-        }
-
-        TorchStrategy::from_mode(
-            mode,
-            python_platform
-                .map(TargetTriple::platform)
-                .as_ref()
-                .unwrap_or(interpreter.platform())
-                .os(),
-        )
-    }).transpose()?;
+    let torch_backend = torch_backend
+        .map(|mode| {
+            TorchStrategy::from_mode(
+                mode,
+                python_platform
+                    .map(TargetTriple::platform)
+                    .as_ref()
+                    .unwrap_or(interpreter.platform())
+                    .os(),
+            )
+        })
+        .transpose()?;
 
     // Initialize the registry client.
     let client = RegistryClientBuilder::try_from(client_builder)?

docs/guides/integration/pytorch.md

@@ -433,11 +433,14 @@ $ uv pip install torch torchvision torchaudio --index-url https://download.pytor
 
 ## Automatic backend selection
 
-In [preview](../../reference/settings.md#preview), uv can automatically select the appropriate
-PyTorch index at runtime by inspecting the system configuration via `--torch-backend=auto` (or
-`UV_TORCH_BACKEND=auto`):
+uv supports automatic selection of the appropriate PyTorch index via the `--torch-backend=auto`
+command-line argument (or the `UV_TORCH_BACKEND=auto` environment variable), as in:
 
 ```shell
+$ # With a command-line argument.
+$ uv pip install torch --torch-backend=auto
+
+$ # With an environment variable.
 $ UV_TORCH_BACKEND=auto uv pip install torch
 ```
 
@@ -446,12 +449,16 @@ PyTorch index for all relevant packages (e.g., `torch`, `torchvision`, etc.). If
 is found, uv will fall back to the CPU-only index. uv will continue to respect existing index
 configuration for any packages outside the PyTorch ecosystem.
 
-To select a specific backend (e.g., `cu126`), set `--torch-backend=cu126` (or
-`UV_TORCH_BACKEND=cu126`).
+You can also select a specific backend (e.g., CUDA 12.6) with `--torch-backend=cu126` (or
+`UV_TORCH_BACKEND=cu126`):
+
+```shell
+$ # With a command-line argument.
+$ uv pip install torch torchvision --torch-backend=cu126
+
+$ # With an environment variable.
+$ UV_TORCH_BACKEND=cu126 uv pip install torch torchvision
+```
 
 At present, `--torch-backend` is only available in the `uv pip` interface, and only supports
 detection of CUDA drivers (as opposed to other accelerators like ROCm or Intel GPUs).
-
-As `--torch-backend` is a preview feature, it should be considered experimental and is not governed
-by uv's standard [versioning policy](../../reference/policies/versioning.md). `--torch-backend` may
-change or be removed entirely in future versions of uv.