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

# Does APIYI Support OpenAI Fast / Ultrafast Mode?

> APIYI does not currently support OpenAI service_tier levels (Fast, Ultrafast, Priority, Flex). Passing one does not error, but the request is processed and billed at the standard tier.

## Short Answer

**Not at the moment.** A request that includes `service_tier` (`fast`, `ultrafast`, `priority`, `flex`) **does not error** and still returns 200, but it is actually processed at the **standard tier (default)**:

* Speed is the same as without the parameter: no faster, no slower
* Billing uses the model's standard price, **with no surcharge and no discount**
* `/v1/responses` returns `service_tier` as `"default"`; `/v1/chat/completions` does not include the field

So there is no need to send this parameter for now, and sending it never costs extra.

## What These Tiers Are

OpenAI uses the `service_tier` parameter to select a processing tier:

| Tier | Request value | OpenAI's description |
| - | - | - |
| Fast (formerly Priority) | `fast`; the old value `priority` still works | Renamed from Priority on 2026-07-30; faster, priced above the standard tier |
| Ultrafast | `ultrafast` | The fastest tier; only `gpt-6.1-sol` and `gpt-6-astra`, Responses API only, priced well above the standard tier |
| Flex | `flex` | Slower and cheaper; returns 429 when provider-side capacity is short |
| Standard | Omitted, or `auto` / `default` | The default tier |

None of these tiers currently takes effect on APIYI. Every request is handled at the standard tier.

## Test Results

On 2026-10-13 we tested `gpt-6.1-sol` and `gpt-6-luna` in both the default group and the OpenAI official group. Both endpoints and all four tiers returned 200:

| Observation | Result |
| - | - |
| `service_tier` returned by `/v1/responses` | Always `default` |
| `service_tier` returned by `/v1/chat/completions` | Field not returned |
| Latency and output speed | No difference from requests without the parameter |
| Console billing | Standard price, identical to requests without the parameter |

> [!TIP]
>
> If your code already sends `service_tier: "priority"` or `"auto"`, you can leave it as is. It affects neither the call nor the billing.

## If You Need It

If your workload genuinely needs the low latency of Fast or Ultrafast, contact support with your use case and expected volume. We will evaluate whether to enable it and announce the billing method if we do.

## Related Docs

> **[What Does an OpenAI Model Refusal Look Like?](/en/faq/openai-content-safety-refusal)**
>
> GPT refusals return 200 with no error code or category

> **[How Do I Avoid API Timeouts?](/en/faq/timeout-configuration)**
>
> Reasoning models take longer, so leave enough client timeout


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