The Cost of Context: StepFun’s Cache-First Economics

At $0.05 per million tokens, StepFun’s cache-read rate makes a specific economic proposition: it costs exactly one-twentieth of the model’s standard input price to re-read context. The listing’s own pricing line reads: “Step 5 Preview costs $1.00/M input tokens and $2.70/M output tokens, with separate rates for Cache Read at $0.05/M tokens.” The mechanism behind that rate, prefix caching , lets a provider store the leading portion of a prompt (system instructions, tool definitions, documents, prior turns) and charge a fraction of input price to read it again on the next call instead of reprocessing it.