> ## Documentation Index
> Fetch the complete documentation index at: https://docs.parallel.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# OpenAI Responses Compatibility

> Field-by-field compatibility reference for the OpenAI Responses wire format

The Responses API models the canonical OpenAI Responses request
(`POST https://api.parallel.ai/v1/responses`), so a stock `openai` SDK client works by
changing only `base_url`, `api_key`, and `model`. This page documents exactly which fields
are honored, which are accepted for SDK compatibility but ignored, and which are rejected.

## Request fields

### Honored

| Field                  | Type                                      | Meaning                                                                                                                                                         |
| ---------------------- | ----------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `model`                | `string`                                  | Must be `"parallel"` — the only model. The tier is chosen via `reasoning.effort`.                                                                               |
| `input`                | `string` \| `message[]`                   | The question, or a list of `{role, content}` messages. **Text only.** Must be non-empty and contain at least one `user` message.                                |
| `reasoning`            | `{"effort": "low" \| "medium" \| "high"}` | Selects the tier. Defaults to `medium`.                                                                                                                         |
| `instructions`         | `string`                                  | System instructions prepended to the request.                                                                                                                   |
| `text`                 | `object`                                  | Text-output config, including [structured output](/responses-api/features/structured-outputs) — structured content is returned JSON-encoded in the output text. |
| `stream`               | `boolean`                                 | [SSE streaming](/responses-api/features/streaming-events). The answer currently arrives as a single text delta, not token-by-token.                             |
| `previous_response_id` | `string`                                  | Prior response id, for [multi-turn context](/responses-api/features/statefulness).                                                                              |
| `metadata`             | `{string: string}`                        | Arbitrary tags echoed back on the response. Max 16 keys, ≤64 chars/key, ≤512 chars/value.                                                                       |

### Accepted but ignored (for SDK compatibility)

`tools`, `tool_choice`, `parallel_tool_calls`, `temperature`, `top_p`, `max_output_tokens`,
`truncation`, `store`, `user`, `include`.

These are part of the OpenAI contract so a stock SDK client's payload never fails
validation, but the backend does not act on them today. Notably you do not pass
`tools: [{"type": "web_search"}]` — grounding is automatic. `store` is likewise ignored:
responses are always stored so they can be referenced via `previous_response_id` (see
[Statefulness](/responses-api/features/statefulness)). Unknown top-level fields are
silently dropped, so newer OpenAI SDK versions won't break.

<Note>
  Ignored fields come back on the response object with their **default values**
  (`temperature: null`, `tools: []`, `tool_choice: "auto"`), not the values you sent.
</Note>

### Rejected

| Request                           | Error                                                                                                                                                              |
| --------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `background: true`                | `400` — "background mode is not supported on /v1/responses; submit long-running work via the [Task API](/task-api/task-quickstart) (POST /v1/tasks/runs) instead." |
| Non-text (multimodal) input parts | `400` — "input contains unsupported non-text content parts: input\_image (this endpoint only accepts text input today)"                                            |
| Empty `input`                     | `400` — "input must not be empty."                                                                                                                                 |
| `input` with no `user` message    | `400` — "input must contain at least one user message."                                                                                                            |
| Any `model` other than `parallel` | `400` — "The Responses API only supports model 'parallel'."                                                                                                        |

Errors use the standard OpenAI error envelope:

```json theme={"system"}
{
  "error": {
    "message": "The Responses API only supports model 'parallel'.",
    "type": "invalid_request_error",
    "param": null,
    "code": null
  }
}
```

Requests over your quota return `429` — back off and retry, and see
[rate limits](/getting-started/rate-limits) for current limits.

## Response fields

A standard OpenAI Responses object. The fields you'll typically read:

| Field         | Meaning                                                                 |
| ------------- | ----------------------------------------------------------------------- |
| `output_text` | The final answer string (SDK convenience accessor).                     |
| `output[]`    | Output items; the `message` item's `content[]` carries the answer text. |
| `usage`       | Token counts (`input_tokens`, `output_tokens`, `total_tokens`).         |
| `id`          | Response id — pass as `previous_response_id` for follow-ups.            |
| `metadata`    | Your request metadata, echoed back.                                     |

<Note>
  `reasoning` and `text` are echoed as `null` on the response even when they were sent and
  honored — read the tier from your request, not the response. Source citations are returned
  as `url_citation` annotations on the output text — see
  [Citations](/responses-api/features/citations).
</Note>