> ## Documentation Index > Fetch the complete documentation index at: https://docs.unprice.dev/llms.txt > Use this file to discover all available pages before exploring further. # Pricing overview > How Unprice models request-path authorization, plan versions, and invoice evidence. For usage-based products, pricing is a runtime decision and an evidence trail. The important moment is not only the invoice. It is the paid action in your product: an API request, LLM call, workflow, data job, export, or tool run that can create cost before billing catches up. Unprice connects that action to one customer money path: ```text theme={null} paid action -> plan version -> pricing rule -> meter -> entitlement -> budget -> wallet -> invoice evidence ``` ## Core model | Concept | What it does | Why it matters | | ---------------- | --------------------------------------------------- | ------------------------------------------------------------- | | Plan | Commercial package your team sells | Groups features into an offer | | Plan version | Published snapshot of pricing and entitlement rules | Keeps existing customers on the pricing they bought | | Feature | Sellable or gateable product capability | Gives your app a stable slug to check | | Meter | Rule that turns events into usage | Powers usage limits, spend, and invoice evidence | | Entitlement | Customer's right or limit for a feature | Lets your app check what the customer can do | | Budget | Customer or workload spend cap | Stops over-budget work before it runs | | Wallet credit | Spend balance held for a customer | Separates money/credits from entitlement grants | | Invoice evidence | Trail from decision to charge | Explains why a line was billed, denied, credited, or replayed | ## Runtime calls Use these calls inside your product: * `access.check` asks whether a customer can use a feature without changing state. * `usage.consume` synchronously applies known usage and returns the allow or deny decision. * `usage.record` asynchronously reports usage for metering and evidence. * `runs.start`, `runs.consume`, and `runs.end` reserve and consume a budget for multi-step work. Read [Choose the runtime call](/quickstart/choose-operation) before wiring production enforcement. ## PriceOps underneath PriceOps is the operating model behind Unprice: plans, plan versions, subscriptions, entitlements, meters, budgets, credits, usage evidence, and invoice evidence stay separate but connected. That separation is what lets you: * authorize customer spend before paid work runs * keep existing customers pinned to the plan version they bought * change packaging without rewriting product code * explain charges from plan, usage, wallet, ledger, and billing evidence ## Next steps Learn how plans and immutable versions keep pricing changes safe. Learn how events become period-scoped usage.