Support Python 3.15

SciPy 1.18.1 (21 August 2026) is the first release to publish `cp315` wheels,
which was the whole block: `utils/lapackdrivers.pyx` does
`from scipy.linalg.cython_lapack cimport ...`, so SciPy is a build dependency
and the extensions did not compile on 3.15 at all.

Adds 3.15 to the CI test matrix, to `[tool.cibuildwheel] build`, and to the
classifiers, with `allow-prereleases` on the test job's `setup-python` since
3.15 is at rc2. Verified locally against 3.15.0rc1: the wheel builds under
meson-python and all 57 tests pass, no source changes needed.

The matrix comment gains "stable". macOS and Windows stay on 3.14 — as they
also do in pylu — so "newest Python" stopped describing the matrix once Linux
went to 3.15.

Removes the deferred item that recorded the block; the one-command check it
carried now passes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J1djVVwJCFVPARVfV6qK67

Author: Technologicat

.github/workflows/ci.yml

@@ -47,7 +47,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        # Full Python matrix on Linux; newest Python only on macOS and Windows.
+        # Full Python matrix on Linux; newest stable Python only on macOS and Windows.
         # Rationale: this `test` job exists for fast feedback ahead of the
         # `build-wheels` job, which runs `cibuildwheel` on every (Python × OS)
         # combination anyway.  Duplicating the full 12-job matrix here would
@@ -58,7 +58,7 @@ jobs:
         # cibuildwheel as the comprehensive backstop for ABI/build regressions
         # on older Pythons across all three OSes.
         os: [ubuntu-latest]
-        python-version: ["3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.11", "3.12", "3.13", "3.14", "3.15"]
         include:
           - os: macos-latest
             python-version: "3.14"
@@ -71,6 +71,11 @@ jobs:
       - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
         with:
           python-version: ${{ matrix.python-version }}
+          # 3.15 is at rc2, which the setup-python manifest marks unstable, so a bare
+          # "3.15" resolves to nothing without this. Versions with a stable release
+          # are unaffected — the prerelease is only a fallback when no stable one
+          # satisfies the request. Becomes a no-op once 3.15 final ships.
+          allow-prereleases: true
 
       # Apple Clang does not ship an OpenMP runtime; install libomp so that
       # meson's `dependency('openmp', required: false)` can find it. If meson

CHANGELOG.md

@@ -2,7 +2,13 @@
 
 ## v1.0.1 (in progress)
 
-*No user-visible changes yet.*
+### New
+
+- **Python 3.15 supported.**
+  - Pre-built wheels on PyPI for Linux, macOS, and Windows, as for 3.11 – 3.14.
+  - SciPy 1.18.1 is the first release to publish `cp315` wheels, so that is what
+    a 3.15 install resolves to. SciPy is a build dependency here, not only a
+    runtime one, so an older pinned SciPy will not work on 3.15.
 
 
 ## v1.0.0 (15 April 2026)

TODO_DEFERRED.md

@@ -59,34 +59,3 @@ applied to neighbor points (e.g. distance-based decay). wlsqm currently has
 only `WEIGHT_UNIFORM` and `WEIGHT_CENTER`. Adding a user-supplied radial
 weight function would be a natural extension and improves robustness against
 outliers.
-
-## Python 3.15 support, once SciPy ships `cp315` wheels
-
-wlsqm is the one project in the fleet that cannot take 3.15 yet, and the block
-is entirely external. `utils/lapackdrivers.pyx` does
-`from scipy.linalg.cython_lapack cimport ...`, which makes SciPy a *build*
-dependency, not merely a runtime one — so no SciPy on 3.15 means the extensions
-do not compile at all, and neither the `test` job nor `cibuildwheel` can run.
-
-Checked 2026-08-18 against PyPI: `pip install --only-binary=:all: scipy` under
-3.15.0rc1 reports "no matching distribution", and no SciPy release publishes a
-`cp315` wheel. Building SciPy from source inside a manylinux container to get
-around this is not worth it — it needs a Fortran toolchain and BLAS, and the
-whole point of the wheel job is that it is reproducible.
-
-Expect this to clear itself some weeks after 3.15 final, when SciPy cuts a
-release with `cp315` wheels. The check is one command; when it passes, the edit
-is the same one the other two Cython projects already took:
-
-```bash
-pip install --only-binary=:all: --dry-run scipy   # under a 3.15 interpreter
-```
-
-- `pyproject.toml`: add `"Programming Language :: Python :: 3.15"` and
-  `cp315-*` to `[tool.cibuildwheel] build`.
-- `.github/workflows/ci.yml`: add `"3.15"` to the `test` matrix and
-  `allow-prereleases: true` to its `setup-python` step (drop the flag once 3.15
-  is final).
-
-Deferred during the fleet-wide Python 3.15 pass (2026-08-18), where pylu, pydgq,
-chandra and arxiv-api-search all went green.

pyproject.toml

@@ -34,6 +34,7 @@ classifiers = [
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: 3.14",
+    "Programming Language :: Python :: 3.15",
     "Topic :: Scientific/Engineering",
     "Topic :: Scientific/Engineering :: Mathematics",
 ]
@@ -115,7 +116,7 @@ ignore = [
 ]
 
 [tool.cibuildwheel]
-build = "cp311-* cp312-* cp313-* cp314-*"
+build = "cp311-* cp312-* cp313-* cp314-* cp315-*"
 skip = "*-win32 *-manylinux_i686 *-musllinux*"
 test-requires = ["pytest", "numpy", "scipy"]
 test-command = "pytest {project}/tests -v"