The `cudaCapabilities` configuration option specifies a list of CUDA capabilities. Packages may use this option to control device code generation to take advantage of architecture-specific functionality, speed up compile times by producing less device code, or slim package closures. For example, you can build for Ada Lovelace GPUs with `cudaCapabilities = [ "8.9" ];`. If `cudaCapabilities` is not provided, the default value is calculated per-package set, derived from a list of GPUs supported by that CUDA version. Please consult [supported GPUs](https://en.wikipedia.org/wiki/CUDA#GPUs_supported) for specific cards. Library maintainers should consult [NVCC Docs](https://docs.nvidia.com/cuda/cuda-compiler-driver-nvcc/) and its release notes.

::: {.caution}
Certain CUDA capabilities are not targeted by default, including capabilities belonging to the Jetson family of devices (e.g. `8.7`, which corresponds to the Jetson Orin) or non-baseline feature-sets (e.g. `9.0a`, which corresponds to the Hopper exclusive feature set). If you need to target these capabilities, you must explicitly set `cudaCapabilities` to include them.
:::

The `cudaForwardCompat` boolean configuration option determines whether PTX support for future hardware is enabled.

### Modifying CUDA package sets {#cuda-modifying-cuda-package-sets}

CUDA package sets are created by using `callPackage` on `pkgs/top-level/cuda-packages.nix` with an explicit argument for `cudaMajorMinorVersion`, a string of the form `"<major>.<minor>"` (e.g., `"12.2"`), which informs the CUDA package set tooling which version of CUDA to use. The majority of the CUDA package set tooling is available through the top-level attribute set `_cuda`, a fixed-point defined outside the CUDA package sets.

::: {.caution}
The `cudaMajorMinorVersion` and `_cuda` attributes are not part of the CUDA package set fixed-point, but are instead provided by `callPackage` from the top-level in the construction of the package set. As such, they must be modified via the package set's `override` attribute.
:::

::: {.caution}
As indicated by the underscore prefix, `_cuda` is an implementation detail and no guarantees are provided with respect to its stability or API. The `_cuda` attribute set is exposed only to ease creation or modification of CUDA package sets by expert, out-of-tree users.
:::

::: {.note}
The `_cuda` attribute set fixed-point should be modified through its `extend` attribute.
:::

The `_cuda.fixups` attribute set is a mapping from package name (`pname`) to a `callPackage`-compatible expression which will be provided to `overrideAttrs` on the result of our generic builder.

::: {.caution}
Fixups are chosen from `_cuda.fixups` by `pname`. As a result, packages with multiple versions (e.g., `cudnn`, `cudnn_8_9`, etc.) all share a single fixup function (i.e., `_cuda.fixups.cudnn`, which is `pkgs/development/cuda-modules/fixups/cudnn.nix`).
:::

As an example, you can change the fixup function used for cuDNN for only the default CUDA package set with this overlay:

```nix
final: prev: {
  cudaPackages = prev.cudaPackages.override (prevArgs: {
    _cuda = prevArgs._cuda.extend (
      _: prevAttrs: {
        fixups = prevAttrs.fixups // {
          cudnn = <your-fixup-function>;
        };
      }
    );
  });
}
```

### Extending CUDA package sets {#cuda-extending-cuda-package-sets}

CUDA package sets are scopes and provide the usual `overrideScope` attribute for overriding package attributes (see the note about `cudaMajorMinorVersion` and `_cuda` in [Configuring CUDA package sets](#cuda-modifying-cuda-package-sets)).

Inspired by `pythonPackagesExtensions`, the `_cuda.extensions` attribute is a list of extensions applied to every version of the CUDA package set, allowing modification of all versions of the CUDA package set without needing to know their names or explicitly enumerate and modify them. As an example, disabling `cuda_compat` across all CUDA package sets can be accomplished with this overlay: