abi3

abi3 is a designation used in CPython extension development to denote a version of the Python C API that provides a stable application binary interface across Python 3.x minor versions. It is part of the Python stable ABI initiative, which aims to let binary extensions be compiled once and loaded on multiple interpreter versions that support the stable API.

Extensions that target the abi3 level are built against the stable surface of the Python C API, often by compiling with the limited API (Py_LIMITED_API). Such modules expose a fixed set of APIs and data structures and do not depend on interpreter internals that may change between minor releases. When a module is compiled with abi3, it can be loaded by any Python 3.x interpreter that implements the stable ABI.

Usage examples: The Rust binding PyO3 supports generating modules that depend on abi3 to enable portability across Python versions. C extensions written with the stable API can also be distributed as abi3 wheels. Packaging tools and build systems, such as maturin or setuptools with a compatible build backend, can produce wheels that target abi3.

Limitations: The stable ABI is deliberately narrower than the full API. Some newer Python features and C API entries are not available under abi3; developers may need to maintain separate code paths or drop reliance on non-stable APIs. Performance and behavior may differ slightly across interpreters, and major Python version upgrades still require recompilation if the stable API changes or if the interpreter does not implement the stable ABI.

See also: CPython, Python C API, Py_LIMITED_API, PEP 384, PyO3, CFFI.