Claude 4.5 streams partial tool call arguments (create_new_file fails with empty filepath)

[BraianRosales]

Hi everyone 👋

I think I found a bug when running tool calls with Claude 4.5 inside Continue.
It seems the model is streaming partial fragments of the arguments JSON instead of sending one complete JSON object.

Here’s what I see in the logs:

Tool call: {
  "id": "toolu_01Mr4T5pDc8pUvEbZq6WxmZC",
  "type": "function",
  "function": {
    "name": "create_new_file",
    "arguments": ""
  }
}
Tool call: {
  "id": "toolu_01Mr4T5pDc8pUvEbZq6WxmZC",
  "type": "function",
  "function": {
    "name": "create_new_file",
    "arguments": "{\"f"
  }
}
Tool call: {
  "id": "toolu_01Mr4T5pDc8pUvEbZq6WxmZC",
  "type": "function",
  "function": {
    "name": "create_new_file",
    "arguments": "ilepath\": \"r"
  }
}
Tool call: {
  "id": "toolu_01Mr4T5pDc8pUvEbZq6WxmZC",
  "type": "function",
  "function": {
    "name": "create_new_file",
    "arguments": "equerimi"
  }
}
Tool call: {
  "id": "toolu_01Mr4T5pDc8pUvEbZq6WxmZC",
  "type": "function",
  "function": {
    "name": "create_new_file",
    "arguments": "en"
  }
}
Tool call: {
  "id": "toolu_01Mr4T5pDc8pUvEbZq6WxmZC",
  "type": "function",
  "function": {
    "name": "create_new_file",
    "arguments": "tos/"
  }
}
Tool call: {
  "id": "toolu_01Mr4T5pDc8pUvEbZq6WxmZC",
  "type": "function",
  "function": {
    "name": "create_new_file",
    "arguments": "A10-Simulac"
  }
}

Because of this, the tool throws the error:
filepath argument is required and must not be empty.

This only happens with Claude 4.5 — GPT-4 and GPT-5 send the full JSON correctly.
So it looks like Continue isn’t buffering or reconstructing the streamed arguments chunks before parsing them.

Expected behavior:
The tool call should receive a complete JSON object (with filepath and contents), not incremental fragments.

Actual behavior:
The tool handler receives multiple partial chunks of arguments, resulting in invalid JSON and tool failure.

Has anyone else seen this issue?
Maybe the fix needs to happen in the Anthropic handler or in the tool execution middleware?

Thanks! 🙏