Development workflow

Day-to-day cycle

# 1. Get up to date
git fetch origin
git checkout -b my-feature origin/main

# 2. Build (incremental builds reuse most of the previous compilation)
pip install -e . -v --no-build-isolation

# 3. Iterate
# ... edit code ...
# rebuild whichever changed:
pip install -e . -v --no-build-isolation
# or for Python-only changes, no rebuild needed (editable install)

# 4. Run a relevant test subset
python test/test_torch.py -v -k matmul
python test/test_nn.py -v
pytest test/inductor/test_torchinductor.py -k vec_kernel

# 5. Lint
spin lint
spin fixlint   # apply auto-fixes

# 6. Push and open a PR
git push -u origin my-feature
# Open the PR via the GitHub UI (or `gh pr create`).

Common build environment variables

Variable	Effect
USE_CUDA=0	CPU-only build (much faster)
USE_DISTRIBUTED=0	Skip building distributed C++ bits
MAX_JOBS=N	Limit parallel build jobs
DEBUG=1	Build with debug symbols (-O0 -g)
REL_WITH_DEB_INFO=1	Release build with debug info
BUILD_TEST=0	Skip C++ test binaries
TORCH_CUDA_ARCH_LIST	Compile only specific GPU architectures (e.g., 8.0;9.0)
CMAKE_BUILD_PARALLEL_LEVEL	Parallelism for CMake
BUILD_CAFFE2=0	Skip Caffe2 (almost always desirable)

The full list lives in setup.py and CMakeLists.txt. For the canonical build command and rationale see CLAUDE.md and README.md.

CI flow tags

PyTorch CI uses ciflow tags to opt PRs into additional test sets:

Tag	What it runs
ciflow/trunk	Same as the post-merge trunk CI
ciflow/inductor	Full inductor test suite
ciflow/dynamo	Dynamo test suite
ciflow/torchtitan	Torchtitan integration
ciflow/rocm-mi300	ROCm MI300 jobs
ciflow/h100	H100 inductor perf jobs
ciflow/mps	MPS tests on macOS
ciflow/binaries	Build wheels for all platforms
ciflow/periodic-rocm-mi300	Long-running ROCm tests

Add a tag by labelling the PR. The merge bot won't merge until the relevant CI is green.

ghstack

Inside Meta and for stacked PRs ghstack is the canonical tool. Per CLAUDE.md:

• ghstack creates one branch per stack entry under gh/USERNAME/N.
• Don't git push to those branches; let ghstack manage them.
• Preserve the Pull-Request: and ghstack-source-id: trailers in commit messages.
• Use ghstack --no-stack to update only the current commit's PR; full ghstack updates the whole stack.
• Use ghstack -u to push only an updated commit message (e.g., for editing a PR body).

External contributors can ignore ghstack and use the regular GitHub PR flow.

Reverts

If a landed PR breaks trunk, the merge bot can revert it. Comment @pytorchbot revert -m "<reason>" -c "ghfirst" (or nosignal/landrace/weird) on the original PR. This produces a revert PR that auto-merges.

Troubleshooting CI

• Looks unrelated → click "Re-run jobs" on the GitHub Actions run.
• Flaky test → comment @pytorchbot rebase to pick up trunk fixes.
• Lint failures → spin fixlint locally and push the fix.
• Real failure on a platform you can't reproduce → tag the relevant module owner.

Where to read next

• Testing — test idioms.
• Tooling — spin, lintrunner, codegen.