uv --version
uv 0.4.24 (b9cd54913 2024-10-17)

(base) ➜  temp uv init hello_uv
Initialized project `hello-uv` at `/Users/tom/temp/hello_uv`
(base) ➜  temp cd hello_uv 
(base) ➜  hello_uv git:(main) ✗ ls
README.md      hello.py       pyproject.toml

(base) ➜  hello_uv git:(main) ✗ uv add torch
Using CPython 3.9.12 interpreter at: /Users/tom/opt/anaconda3/bin/python
Creating virtual environment at: .venv
Resolved 24 packages in 44.33s
error: Distribution `torch==2.5.0 @ registry+https://pypi.org/simple` can't be installed because it doesn't have a source distribution or wheel for the current platform

(base) ➜  hello_uv git:(main) ✗ uv add torch --extra-index-url=https://download.pytorch.org/whl/cpu 
warning: Indexes specified via `--extra-index-url` will not be persisted to the `pyproject.toml` file; use `--index` instead.
Resolved 23 packages in 11.67s
error: Distribution `torch==2.5.0 @ registry+https://download.pytorch.org/whl/cpu` can't be installed because it doesn't have a source distribution or wheel for the current platform

(base) ➜  hello_uv git:(main) ✗ uv add torch --index-url=https://download.pytorch.org/whl/cpu      
warning: Indexes specified via `--index-url` will not be persisted to the `pyproject.toml` file; use `--default-index` instead.
Resolved 11 packages in 9.48s
error: Distribution `torch==2.5.0+cpu @ registry+https://download.pytorch.org/whl/cpu` can't be installed because it doesn't have a source distribution or wheel for the current platform

[project]
name = "project"
version = "0.1.0"
dependencies = [
  "torch==2.1.2 ; platform_system != 'Windows'",
]

(base) ➜  hello_uv git:(main) ✗ uv sync            
warning: No `requires-python` value found in the workspace. Defaulting to `>=3.11`.
  × No solution found when resolving dependencies for split (platform_system == 'Windows'):
  ╰─▶ Because there is no version of torch{platform_system == 'Windows'}==2.1.2+cu121 and your project depends on
      torch{platform_system == 'Windows'}==2.1.2+cu121, we can conclude that your project's requirements are unsatisfiable.