Interface UsageModel

For chat interactions, the number of tokens in the assistant's response.
For context retrieval, this is always 0.

For chat interactions, the number of tokens in the LLM request (message, context snippets, and system prompt). For context retrieval, the number of tokens in the LLM request used to generate search queries from the messages, plus the tokens in the retrieved context snippets.

The total number of tokens used, equal to the sum of prompt_tokens and completion_tokens.