---
title: "CustomToolCallInputDeltaEvent"
---

Event emitted when a custom tool call's freeform input is being streamed. Mirrors `response.function_call_arguments.delta` but for `custom` tools whose input is opaque text rather than JSON arguments.


## Fields

| Field                                                                                              | Type                                                                                               | Required                                                                                           | Description                                                                                        |
| -------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------- |
| `delta`                                                                                            | *str*                                                                                              | :heavy_check_mark:                                                                                 | N/A                                                                                                |
| `item_id`                                                                                          | *str*                                                                                              | :heavy_check_mark:                                                                                 | N/A                                                                                                |
| `output_index`                                                                                     | *int*                                                                                              | :heavy_check_mark:                                                                                 | N/A                                                                                                |
| `sequence_number`                                                                                  | *int*                                                                                              | :heavy_check_mark:                                                                                 | N/A                                                                                                |
| `type`                                                                                             | [components.CustomToolCallInputDeltaEventType](../components/customtoolcallinputdeltaeventtype.mdx) | :heavy_check_mark:                                                                                 | N/A                                                                                                |