Can you share more? I'm with OpenRouter and we would love to address this! We don't see this in our own testing, I don't believe -- but will share this feedback and dig in.
Then I read somewhere (I think X) that OpenRouter adds stuff and breaks caching (telemetry? headers? can't remember). So I stopped the job, switched to actual DeepSeek provider, and voilá, caching 3x more tokens per request (on average).
I meant actual DeepSeek API.
Directly: 135M input tokens - $0.57 (134M cached)
Via OpenRouter 6M tokens - $0.81 (caching stats & inp/out not reported)
Caching is a huge win with using deepseek directly.