Most terminal coding agents are architecturally similar: a loop, a tool registry, some context management, a TUI. Reasonix picks a different thing to optimize for, and it is a thing that shows up on your bill rather than in a demo video.
The tagline is "engineered around prefix-cache stability — leave it running." That phrase is doing a lot of work, so let's unpack it.
Why prefix caching is the whole pitch
DeepSeek's API, like several others, caches the prefix of your prompt. If the next request starts with the exact same token sequence as the previous one, the provider serves those tokens from cache and bills them at a small fraction of the normal input rate. Cache hits are dramatically cheaper than cache misses.
Here is the catch: it is a prefix cache. The match has to start at token zero and run forward. Change one character near the top of your context and every token after it is a miss.
