cached versions of packages

[MikeyBeez]

Summary

How Your Idea Would Work

The workflow you're proposing would be a huge quality-of-life improvement. It might look something like this:
Your pyproject.toml has an unpinned dependency like "torch".
You run uv sync.
uv checks its global cache and sees that the last version of torch you installed from the nightly source was 2.7.0.dev20251012.
It then quickly checks the online repository and sees that a newer version, 2.7.0.dev20251013, is available.
Instead of just automatically downloading the new one, it prompts you:
Found a recent version of 'torch' (2.7.0.dev20251012) in your cache.
The latest version available is 2.7.0.dev20251013.

Use the cached version and skip the download? [Y/n]:

Why It's a Great Suggestion

It Promotes Stability by Default: This makes your environment's versions "sticky." They won't change unless you explicitly tell them to, which is much safer than automatically grabbing the latest, potentially broken, nightly build.
It Saves Time and Bandwidth: It directly avoids the slow dependency resolution and re-download process for minor updates.
It's User-Centric: It makes the tool feel more like an intelligent assistant that understands your workflow, rather than just a command executor.

Example

No response

[zanieb]

I don't think we'll add prompting for this, it doesn't really mesh with the overall user experience we're trying to build.

I think you are asking for a similar thing to #16108 though.

It Promotes Stability by Default: This makes your environment's versions "sticky." They won't change unless you explicitly tell them to, which is much safer than automatically grabbing the latest, potentially broken, nightly build.

This is provided by lockfiles. I recommend using them. If you're using uv sync, then you should be already. We don't fetch new versions unless you use --refresh or --upgrade.