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# Parallel execution support in SciPy

SciPy aims to provide functionality that is performant, i.e. has good execution speed. On modern computing hardware, CPUs often have many CPU cores - and hence users may benefit from parallel execution. This page aims to give a brief overview of the options available to employ parallel execution.

Some key points related to parallelism:

- SciPy itself defaults to single-threaded execution.

- The exception to that single-threaded default is code that calls into a BLAS or LAPACK library for linear algebra functionality (either direct or via NumPy). BLAS/LAPACK libraries almost always default to multi-threaded execution, typically using all available CPU cores.

  - Users can control the threading behavior of the BLAS/LAPACK library that SciPy and NumPy are linked with through threadpoolctl.

- SciPy functionality may provide parallel execution in an opt-in manner. This is exposed through a `workers=` keyword in individual APIs, which takes an integer for the number of threads or processes to use, and in some cases also a map-like callable (e.g., `multiprocessing.Pool`). See `scipy.fft.fft` and `scipy.optimize.differential_evolution` for examples.

  - SciPy-internal threading is done with OS-level thread pools. OpenMP is not used within SciPy.

- SciPy works well with `multiprocessing` and with `threading`. The former has higher overhead than the latter, but is widely used and robust. The latter may offer performance benefits for some usage scenarios - however, please read Thread Safety in SciPy.

- SciPy has experimental support for free-threaded CPython, starting with SciPy 1.15.0 (and Python 3.13.0, NumPy 2.1.0).

- SciPy has experimental support in a growing number of submodules and functions for array libraries other than NumPy, such as PyTorch, CuPy and JAX. Those libraries default to parallel execution and may offer significant performance benefits (and GPU execution). See Support for the array API standard for more details.