Breaking changes: Python 3.10 dropped, moving to Stable ABI (cp311-abi3)

[o-murphy]

📢 Breaking changes: Python 3.10 dropped, moving to Stable ABI (cp311-abi3) + NO-GIL support (cp313t)

Hey everyone,

As part of the upcoming 2.3.x release, we're introducing major changes to how we build, test, and publish wheels. This will significantly reduce CI time, cut the number of release artifacts almost in half, and simplify maintenance — though it also adds some new complexity.

🚫 Python 3.10 is no longer supported

Starting from 2.3.x, we are dropping support for Python 3.10.
The new minimum version is Python 3.11.

🧱 New wheel build strategy

1. For GIL‑based Python (standard CPython)

We are switching to the Stable ABI (Limited API) with the target version 0x030B0000 (Python 3.11).

• One universal wheel (cp311-abi3) will work on Python 3.11, 3.12, 3.13, 3.14+
• Instead of 4 separate wheels per platform/architecture → we build 1 universal for all 3.11+ versions

2. For NO‑GIL (free‑threaded Python)

We will build separate wheels for free‑threaded builds:

• cp313t-* (Python 3.13t)
• cp314t-* (Python 3.14t and later)

These wheels are not covered by the Stable ABI (free‑threaded Limited API is still experimental).

📦 Expected impact

Before (2.2.x)	After (2.3.x)
~70 artifacts per release	~35 artifacts
6 wheels per platform+arch	1 universal wheel (3.11+) + 2 free‑threaded wheels
Long build & publish times	~2x faster CI (build + test)
Harder to debug (many variants)	Fewer variants → simpler debugging

⚠️ Trade‑offs

• ✅ Less CI time – fewer builds and test runs
• ✅ Fewer release artifacts – easier to manage
• ✅ Simpler debugging – less matrix explosion
• ❌ Harder maintenance – Stable ABI has some limitations (e.g., typed memoryviews require 3.11+ in practice, some Cython features may be restricted)
• ❌ No more 3.10 – users must upgrade

🧑‍💻 New rule for contributors

From now on, all new contributions must be compatible with:

• Stable ABI cp311-abi3 (Py_LIMITED_API=0x030B0000) for GIL builds
• NO‑GIL builds (cp313t-* / cp314t-*) must not break (free‑threaded safety is encouraged but not yet strictly enforced)

When adding Cython code, please avoid:

• C API functions not included in the Limited API (check Python docs)
• Implicit reliance on the GIL without proper locking (for free‑threaded compatibility)

🔧 Technical notes for maintainers

To build with Stable ABI, our setup.py / pyproject.toml now uses:

Extension(
    ...,
    define_macros=[("Py_LIMITED_API", "0x030B0000")],
    py_limited_api=True,
)

For free‑threaded wheels, we will use the -t ABI tag separately (not part of abi3).

📅 Timeline

• This will take effect in 2.3.x
• Existing 2.2.x releases will continue to support 3.10 and use the old multi‑wheel strategy
• Please test your code with Python 3.11+ and report any Stable ABI / free‑threaded issues

💬 Discussion

Let us know if you have concerns or run into problems. This change should make our release process much leaner, but we're open to feedback!