It appeared to be typosquatting existing crate polymarket-client-sdk (sdks vs sdk) and attempting to steal credentials from local files.
The malicious crate had 1 version published on 2026-02-09 and had been downloaded only 33 times. There were no crates depending on this crate on crates.io.
Thanks to Roland Peelen for finding and reporting this to the crates.io team!