View channel freshness on https://status.nixos.org/. nixpkgs-unstable can be a few days old.
For Nix channel freshness history, check out https://monitoring.nixos.org/grafana/d/LhIq8iLWk/channel-updates?orgId=1&refresh=10s&from=now-30d&to=now.
Use https://nixpk.gs/pr-tracker.html to check progress of a specific nixpkgs PR. For example, https://nixpk.gs/pr-tracker.html?pr=300028.