Make cost fields optional in ResultMessage to handle missing cost data

[r488it]

Summary

Modified the ResultMessage class to make cost_usd and total_cost_usd fields optional, preventing errors when API responses don't include cost information.

Changes Made

• Changed cost_usd field from float to float | None = None in ResultMessage class
• Changed total_cost_usd field from float to float | None = None in ResultMessage class
• Reordered fields to place optional fields at the end of the dataclass

Problem Solved

• API responses sometimes don't include cost information (cost_usd, total_cost)
• Current implementation has these fields commented out in client.py, which could cause initialization errors for ResultMessage
• Need to handle messages reliably regardless of whether cost information is available

Files Modified

• claude_code_sdk/types.py: Updated ResultMessage dataclass definition
• claude_code_sdk/_internal/client.py: Maintained consistency with existing commented-out cost fields

Backward Compatibility

• Existing code using cost information will need to add None checks
• New implementation returns None when cost information is unavailable

Testing

• Verified functionality with responses containing cost information
• Verified functionality with responses missing cost information
• Confirmed existing test cases still pass

Related Issue

This change improves the robustness of the SDK when handling different API response formats and prevents potential runtime errors due to missing cost data.

[musab-mk]

I got this on new Claude CLI update:

• SDK: Renamed total_cost to total_cost_usd

---

It might be related to that.

[106-]

As noted in the CHANGELOG.md, you can replace total_cost with total_cost_usd instead of just commenting it out.
I ran the actual command this library calls internally (tested with version 1.0.24), and got the following result:

$ claude --output-format stream-json --verbose --print "What is 2 + 2?"
...
{
  "type": "result",
  "subtype": "success",
  "is_error": false,
  "duration_ms": 2905,
  "duration_api_ms": 2702,
  "num_turns": 1,
  "result": "4",
  "session_id": "xxx",
  "total_cost_usd": 0.04995525000000001,
  "usage": {
    "input_tokens": 3,
    "cache_creation_input_tokens": 13291,
    "cache_read_input_tokens": 0,
    "output_tokens": 7,
    "server_tool_use": {
      "web_search_requests": 0
    }
  }
}

As you can see, total_cost_usd is indeed present in the response.

[ltawfik]

thank you @r488it, this is fixed with the latest release, pip install --upgrade claude-code-sdk