You definitely trust the same web of trust key graph already in every single layer of your current CI solution. Everything at Astral and by all indications also OpenAI is built with third party services, third party (blind) signing, using third party binaries signed by those 5000 keys directly or indirectly.
That web of trust is the trust foundation of the entire internet and likely every server that powers Github, Astral, and OpenAI including every CI system you described.
https://kron.fi/en/posts/stagex-web-of-trust/
One node in that graph is also nowhere near good enough to stop supply chain attacks, which is why we use -multiple- points thanks to full source bootstrapped deterministic builds.
Let me flip it and ask why anyone should trust that an Astral/OpenAI employee that does not sign their commits and does not sign their reviews, has not been impersonated or had an account takeover due to the phishable 2FA that is allowed, and won't just make a commit to CI stack for uv (or uv itself!) under a pseudonym then merge their pseudonym's code.
One person can burn it all down in spite of the practices in this blog post. Letting machines blindly sign whatever non-deterministic outputs come out of an automated process does not actually buy you much in practice against many of the supply chain attack tactics actually used in the wild. Also of course the same applies to the third party build systems you trust. Github themselves also don't use any of these basic supply chain security practices either so many many points of failure here.
Astral/OpenAI are actually giving -thousands- of randos other than the authors the ability to backdoor the uv binaries you produce, and without a reproducible full source bootstrapped build process, no one would be able to quickly or easily prove it.
To package or change uv in stagex one maintainer must sign the commit, and another must sign the review/merge commit. Then -multiple- maintainers must compile 180 bytes of human readable machine code, build up to tinycc, then gcc, then llvm, and eventually to a rust compiler, that we then use to build uv, all deterministically.
So, we actually don't trust any third parties other than the actual authors of the source code to a limited extent in our process. That said we are working on a solution for decentralized review of upstream code as well right now because we largely don't trust upstreams to not let their identities get stolen because most teams for whatever reason refuse to sign their commits and reviews, so we will have to do that for them too. Regardless, we can prove we faithfully deliver honest compilations of whatever upstream code is published without any single points of failure.
We ask users downloading binaries to trust that a bunch of maintainers are putting their personal reputations and keys (which long predate AI and are hard to impersonate) on the line to sign their bit for bit identical builds of uv, and the entire toolchain underneath it, and provide faithful compilations of upstream source code.
It would make everyone a lot safer if upstreams, especially well funded ones, could meet or exceed the threat model we must support downstream.