Track cost and usage

 For complete API documentation, see the [TypeScript SDK reference](/docs/en/agent-sdk/typescript) and [Python SDK reference](/docs/en/agent-sdk/python).
 
 <Warning>
-  The `total_cost_usd` and `costUSD` fields are client-side estimates, not authoritative billing data. The SDK computes them locally from a price table bundled at build time, so they can drift from what you are actually billed when:
+  The `total_cost_usd` and `costUSD` fields are client-side estimates, not authoritative billing data. The SDK computes them locally from a price table bundled at build time, unless a [`modelPricing`](/docs/en/settings-reference#modelpricing) table is in effect. They can drift from what you are actually billed when:
 
   * pricing changes
   * the installed SDK version does not recognize a model

 ### Break down usage per model
 
 The result message includes [`modelUsage`](/docs/en/agent-sdk/typescript#modelusage), a map of model name to per-model token counts and cost. This is useful when you run multiple models (for example, Haiku for subagents and Opus for the main agent) and want to see where tokens are going.
+
+Each entry's `costBasis` says which price table priced that model's latest request: `list` for list price, `managed` for a [`modelPricing`](/docs/en/settings-reference#modelpricing) table, or `unknown` when neither matched the model ID. The field requires Claude Code v2.1.246 or later.
 
 The following example runs a query and prints the cost and token breakdown for each model used: