> Do all other providers somehow overcharge by that much?

This, I think. Cached inputs have an opportunity cost (keeping the KV cache until use) but a hit is basically free. “Basically” - if the cache is offloaded to system RAM or NVMe there’s some scheduling overhead.

From a consumer viewpoint a more interesting metric than the raw costs is

    cached cost * hitrate + input cost * (1 - hitrate)

from a personal standpoint rather than a per-provider one (e.g. if OpenRouter is blindly dispatching your requests you might have a bad time).