Discounted pricing is available only at https://platform.deepseek.com. All of OpenRouter providers do not match their pricing at the moment.
I was concerned I would need to do something specific in my dumb agent harness to make caching effective, since I'd read Anthropic's reason for forcing people to use Claude Code in order to use the rolling token usage limits on a subscription was because they could control cache behavior more effectively, but DeepSeek seems to be able to handle caching very effectively for raw API calls.