claude-code - 💡(How to fix) Fix Add token usage and cost fields to `Stop` and `UserPromptSubmit` hook events [2 comments, 3 participants]

TL;DR

Adding token usage and cost fields to the Stop and UserPromptSubmit hook events is likely the most effective way to provide real-time cost visibility per interaction.

Guidance

• To calculate per-prompt cost, consider modifying the Stop hook to include token usage and cost data, as proposed in the issue.
• Adding a cumulative cost field to UserPromptSubmit would allow for calculating the delta in cost between prompts.
• Review the existing /cost endpoint to understand how cost data is currently calculated and exposed, as this may inform the implementation of cost tracking in hooks.
• Consider the potential impact of adding cost data to hooks on the overall system performance and user experience.

Example

No explicit code example is provided, but the proposed JSON structure for the Stop hook input suggests how token usage and cost data could be formatted:

{
  "session_id": "abc123",
  "hook_event_name": "Stop",
  "stop_reason": "end_turn",
  "token_usage": {
    "input_tokens": 1500,
    "output_tokens": 800,
    "cache_read_input_tokens": 12000,
    "cache_creation_input_tokens": 3000
  },
  "cost_usd": 0.042,
  "cumulative_cost_usd": 0.58
}

Notes

The implementation details of adding cost data to hooks are not specified in the issue, so the exact steps and potential challenges are unclear.

Recommendation

Apply workaround: Modify the Stop and UserPromptSubmit hook events to include token usage and cost data, as this would provide the necessary information for calculating per-prompt costs without requiring significant changes to the existing system.