Update BUILD.md with multi-Python build instructions

BUILD.md

@@ -2,8 +2,17 @@
 
 **Built:** 2026-04-07
 **Target:** DGX Spark (GB10 Blackwell, aarch64, SM 10.0 + SM 12.1)
-**Wheel:** `dist/tensorflow-2.21.0-cp310-cp310-linux_aarch64.whl` (377 MB)
-**Build time:** ~1.5 hours
+**HuggingFace:** [Qanatpharma/tensorflow-2.21.0-cuda13-aarch64](https://huggingface.co/Qanatpharma/tensorflow-2.21.0-cuda13-aarch64)
+**Build time:** ~2 hours per Python version
+
+## Available Wheels
+
+| Python | Wheel | Size |
+|--------|-------|------|
+| 3.10 | `tensorflow-2.21.0-cp310-cp310-linux_aarch64.whl` | 377 MB |
+| 3.11 | `tensorflow-2.21.0-cp311-cp311-linux_aarch64.whl` | 377 MB |
+| 3.12 | `tensorflow-2.21.0-cp312-cp312-linux_aarch64.whl` | 377 MB |
+| 3.13 | `tensorflow-2.21.0-cp313-cp313-linux_aarch64.whl` | 378 MB |
 
 ## Build Configuration
 
@@ -104,19 +113,46 @@ echo 'build:cuda --repo_env LOCAL_CUDNN_PATH="/home/philipptrepte/bioai/tools/te
 
 ### 6. Build
 
+The `HERMETIC_PYTHON_VERSION` flag controls which Python the wheel targets.
+Each version requires a full rebuild (~2 hours).
+
 ```bash
+# Python 3.10 (default if HERMETIC_PYTHON_VERSION is omitted)
 bazel build \
   --config=cuda_wheel \
   --config=opt \
   --copt=-march=armv9-a \
   --verbose_failures \
   --repo_env=HERMETIC_NVSHMEM_VERSION="" \
+  --repo_env=HERMETIC_PYTHON_VERSION=3.10 \
+  //tensorflow/tools/pip_package:wheel
+```
+
+For other Python versions, change the env and re-configure first:
+
+```bash
+# Example: Python 3.12
+conda create -n tf-build-312 python=3.12 numpy -y
+conda activate tf-build-312
+pip install numpy wheel packaging requests
+
+# Re-run configure (sets PYTHON_BIN_PATH for the new env)
+export PYTHON_BIN_PATH=$(which python)
+# ... same env vars as step 5 ...
+./configure
+echo 'build:cuda --repo_env LOCAL_CUDNN_PATH=".../cudnn"' >> .tf_configure.bazelrc
+
+# Build with matching hermetic Python
+bazel build \
+  --config=cuda_wheel --config=opt --copt=-march=armv9-a \
+  --verbose_failures --repo_env=HERMETIC_NVSHMEM_VERSION="" \
+  --repo_env=HERMETIC_PYTHON_VERSION=3.12 \
   //tensorflow/tools/pip_package:wheel
 ```
 
 The wheel lands at:
 ```
-bazel-bin/tensorflow/tools/pip_package/wheel_house/tensorflow-2.21.0-cp310-cp310-linux_aarch64.whl
+bazel-bin/tensorflow/tools/pip_package/wheel_house/tensorflow-2.21.0-cp3XX-cp3XX-linux_aarch64.whl
 ```
 
 Copy to dist:
@@ -128,7 +164,7 @@ cp bazel-bin/tensorflow/tools/pip_package/wheel_house/*.whl ../dist/
 ### 7. Install
 
 ```bash
-pip install ~/bioai/tools/tensorflow-build/dist/tensorflow-2.21.0-cp310-cp310-linux_aarch64.whl
+pip install ~/bioai/tools/tensorflow-build/dist/tensorflow-2.21.0-cp3XX-cp3XX-linux_aarch64.whl
 ```
 
 ### 8. Verify