Enable Python 3.15 / 3.15t by default in the binary build matrix (#8427)

## What

Promotes **Python 3.15 / 3.15t** from opt-in preview to the **default**
binary
build matrix, on **all operating systems**, for the **nightly** and
**test**
channels. Follow-up to #8241, which added them as opt-in.

- `3.15`, `3.15t` added to `PYTHON_ARCHES_DICT["nightly"]` and
`["test"]`
- `PREVIEW_PYTHON_ARCHES_DICT` deleted
- the `INCLUDE_PREVIEW_PYTHON_VERSIONS` env var, the
  `--include-preview-python-versions` CLI flag, the
  `include-preview-python-versions` reusable-workflow input, and the
  `include_preview_python_versions` parameter threaded through
`generate_build_matrix` / `generate_wheels_matrix` /
`generate_libtorch_matrix`
  are all removed
- the two `include-preview-python-versions: enable` call sites in
`validate-linux-binaries.yml` and `validate-aarch64-linux-binaries.yml`
are
  dropped, since the behaviour is now the default

**`release` deliberately keeps 3.15 out.** 3.15 is still a CPython
pre-release
(wheels are built against 3.15.0b4), so it must not land in the release
matrix or
on the getting-started page until it ships final. This is the one
channel that
still differs, and it is now the only reason `PYTHON_ARCHES_DICT` has an
asymmetric entry.

Resulting default python versions per OS/channel:

| os | nightly / test | release |
|---|---|---|
| linux | +3.15, +3.15t | unchanged |
| linux-aarch64 | +3.15, +3.15t | unchanged |
| windows | +3.15, +3.15t | unchanged |
| macos-arm64 | +3.15, +3.15t | unchanged |
| windows-arm64 | unchanged (pins its own `3.11/3.12/3.13` list) |
unchanged |

`TORCH_ONLY_PYTHON_ARCHES` is untouched, so 3.15 install commands stay
torch-only (no torchvision wheels for 3.15 yet).

## Reviewer notes — three things worth a look

1. **Removing the reusable-workflow input is breaking for any external
caller.**
Passing an undefined input to a reusable workflow is a hard error in
GitHub
Actions. `grep` finds only the two in-repo call sites (both removed
here), and
the input is ~1 month old, so downstream repos are unlikely to reference
it —
but if any do, they break on merge. Happy to keep it as an
accepted-but-ignored
   input for a deprecation window instead.

2. **No macOS point-version pin was added for 3.15, on purpose.**
`MACOS_PYTHON_POINT_VERSIONS` has no `3.15` entry, so macOS falls
through
`.get(python_version, python_version)` to plain `3.15` / `3.15t` — the
same
treatment `3.13` and `3.14t` already get. This is required for
correctness:
   that value feeds `conda create "python=${PYTHON_VERSION}"` in
`setup-binary-builds`, whose `case` arms match on exactly `3.15)` /
`3.15t)` to
   swap in `3.15.0b4` plus the `conda-forge/label/python_dev` +
`python_rc` channels. A `3.15.0b1`-style pin here would miss those arms
and the
   solve would fail.

3. **Windows 3.15 and the openssl pin.** `setup-binary-builds` clears
`OPENSSL_PIN` for 3.15 because the beta requires `openssl>=3.5.7`, and
the
old comment justified that with "3.15 is Linux-only". That is no longer
true,
so Windows 3.15 builds are now exposed to the openssl 3.5.7 ASN.1
regression
at smoke-test time (pytorch/pytorch#186846). I updated the comment to
say so
rather than silently leave a stale rationale; the pin cannot simply be
   re-applied because 3.5.6 is unsatisfiable for the 3.15 beta.

## Test plan

- `python -m tools.tests.test_generate_binary_build_matrix` — **11
passed**
- Reference assets regenerated via `--update-reference-files` (7 asset
files;
  the bulk of the diff)
- Tests rewritten from opt-in semantics to default-on:
- `test_python_3_15_enabled_by_default` — asserts 3.15/3.15t present for
    nightly and test across linux, linux-aarch64, windows, macos-arm64
- `test_python_3_15_excluded_on_release_channel` — asserts absent on
release
    for all four
- `test_python_3_15_excluded_on_windows_arm64` — guards the hardcoded
list
- Spot-checked the generator directly for every os × channel
combination, and
confirmed macOS emits `3.15` / `3.15t` with torch-only install commands.

Co-authored-by: Andrey Talman <atalman@users.noreply.github.com>

Author: atalman

.github/actions/setup-binary-builds/action.yml

@@ -151,9 +151,10 @@ runs:
           # and rejects a malformed cert in the Windows machine cert store,
           # breaking ssl.create_default_context() with "[ASN1: NOT_ENOUGH_DATA]"
           # at smoke-test time. See https://github.com/pytorch/pytorch/pull/186846
-          # The 3.15 cases below clear this: the 3.15 beta requires openssl>=3.5.7,
-          # and 3.15 is Linux-only with its smoke test skipped, so the Windows
-          # regression does not apply.
+          # The 3.15 cases below clear this because the 3.15 beta requires
+          # openssl>=3.5.7, so the 3.5.6 pin is unsatisfiable there. NOTE: 3.15
+          # is no longer Linux-only, so Windows 3.15 builds are exposed to the
+          # ASN.1 regression above until openssl ships a fix.
           export OPENSSL_PIN="openssl=3.5.6"
 
           # shellcheck disable=SC2153

.github/workflows/generate_binary_build_matrix.yml

@@ -52,11 +52,6 @@ on:
         description: "A JSON-encoded list of python versions to build. An empty list means building all supported versions"
         default: "[]"
         type: string
-      include-preview-python-versions:
-        description: "Include opt-in preview python versions (torch-only, Linux x86 and aarch64), e.g. 3.15/3.15t"
-        default: "disable"
-        required: false
-        type: string
       getting-started:
         description: "Release matrix for getting started page"
         required: false
@@ -102,7 +97,6 @@ jobs:
           BUILD_PYTHON_ONLY: ${{ inputs.build-python-only }}
           GETTING_STARTED: ${{ inputs.getting-started }}
           PYTHON_VERSIONS: ${{ inputs.python-versions }}
-          INCLUDE_PREVIEW_PYTHON_VERSIONS: ${{ inputs.include-preview-python-versions }}
         run: |
           set -eou pipefail
           MATRIX_BLOB="$(python3 tools/scripts/generate_binary_build_matrix.py)"

.github/workflows/validate-aarch64-linux-binaries.yml

@@ -99,8 +99,6 @@ jobs:
       with-cuda: enable
       with-cpu: enable
       use-only-dl-pytorch-org: ${{ inputs.use-only-dl-pytorch-org }}
-      # Validate torch-only preview python versions (3.15/3.15t) on the nightly and test channels.
-      include-preview-python-versions: enable
 
   linux-aarch64:
     needs: generate-aarch64-linux-matrix

.github/workflows/validate-linux-binaries.yml

@@ -108,8 +108,6 @@ jobs:
       channel: ${{ inputs.channel }}
       use-only-dl-pytorch-org: ${{ inputs.use-only-dl-pytorch-org }}
       with-xpu: enable
-      # Validate torch-only preview python versions (3.15/3.15t) on the nightly and test channels.
-      include-preview-python-versions: enable
 
   linux:
     needs: generate-linux-matrix

tools/scripts/generate_binary_build_matrix.py

@@ -21,22 +21,16 @@
 from typing import Any, Callable, Dict, List, Optional, Tuple
 
 
+# 3.15 / 3.15t are enabled by default on the nightly and test channels for every
+# operating system. They are deliberately absent from "release": 3.15 is still a
+# CPython pre-release, so it must not appear in the release matrix or on the
+# getting-started page until it ships final.
 PYTHON_ARCHES_DICT = {
-    "nightly": ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"],
-    "test": ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"],
+    "nightly": ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t", "3.15", "3.15t"],
+    "test": ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t", "3.15", "3.15t"],
     "release": ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"],
 }
 
-# Preview Python versions validated for torch only, on Linux x86 and aarch64.
-# These are opt-in via INCLUDE_PREVIEW_PYTHON_VERSIONS so that the shared
-# generator default is unchanged for domain libraries (torchvision, torchaudio)
-# and for Windows/macOS, which do not have wheels for these versions yet.
-PREVIEW_PYTHON_ARCHES_DICT = {
-    "nightly": ["3.15", "3.15t"],
-    "test": ["3.15", "3.15t"],
-    "release": [],
-}
-
 # Python versions for which only torch is validated (no torchvision). torchvision
 # wheels are not published for these versions yet, so the install command must
 # request torch alone.
@@ -350,9 +344,7 @@ def generate_libtorch_matrix(
     abi_versions: Optional[List[str]] = None,
     arches: Optional[List[str]] = None,
     libtorch_variants: Optional[List[str]] = None,
-    include_preview_python_versions: bool = False,
 ) -> List[Dict[str, str]]:
-    # libtorch is python-agnostic; the preview python versions do not apply.
     ret: List[Dict[str, str]] = []
 
     if arches is None:
@@ -444,7 +436,6 @@ def generate_wheels_matrix(
     getting_started: bool = False,
     python_versions: Optional[List[str]] = None,
     arches: Optional[List[str]] = None,
-    include_preview_python_versions: bool = False,
 ) -> List[Dict[str, str]]:
     package_type = "wheel"
 
@@ -454,17 +445,6 @@ def generate_wheels_matrix(
         # Define default python version
         python_versions = list(PYTHON_ARCHES)
 
-        # Opt-in preview versions (e.g. 3.15/3.15t) are torch-only and validated
-        # on Linux x86/aarch64 and macOS arm64. Append them to the default list
-        # so the shared default (used by domain libraries and Windows) is
-        # unaffected.
-        if include_preview_python_versions and os in (
-            LINUX,
-            LINUX_AARCH64,
-            MACOS_ARM64,
-        ):
-            python_versions += PREVIEW_PYTHON_ARCHES_DICT.get(channel, [])
-
     if os == WINDOWS_ARM64:
         python_versions = ["3.11", "3.12", "3.13"]  # only versions for now
 
@@ -564,7 +544,6 @@ def generate_build_matrix(
     build_python_only: str,
     getting_started: str = "false",
     python_versions: Optional[List[str]] = None,
-    include_preview_python_versions: str = "disable",
 ) -> Dict[str, List[Dict[str, str]]]:
     includes = []
 
@@ -594,8 +573,6 @@ def generate_build_matrix(
                     use_only_dl_pytorch_org == "true",
                     getting_started == "true",
                     python_versions,
-                    include_preview_python_versions=include_preview_python_versions
-                    == ENABLE,
                 )
             )
 
@@ -697,15 +674,6 @@ def main(args: List[str]) -> None:
         default=os.getenv("PYTHON_VERSIONS", "[]"),
     )
 
-    parser.add_argument(
-        "--include-preview-python-versions",
-        help="Include opt-in preview python versions (torch-only, Linux x86 and "
-        "aarch64) in the matrix",
-        type=str,
-        choices=[ENABLE, DISABLE],
-        default=os.getenv("INCLUDE_PREVIEW_PYTHON_VERSIONS", DISABLE),
-    )
-
     options = parser.parse_args(args)
     try:
         python_versions = json.loads(options.python_versions)
@@ -729,7 +697,6 @@ def main(args: List[str]) -> None:
         options.build_python_only,
         options.getting_started,
         python_versions,
-        options.include_preview_python_versions,
     )
 
     print(json.dumps(build_matrix))