Service tiers

Several providers sell the same model at more than one processing tier. Flex runs your request on spare capacity for about half the price, in exchange for slower and less predictable responses. Priority puts your request ahead of standard traffic for faster tokens, at a premium. Opper exposes these tiers with the same service_tier field OpenAI uses, on every provider that offers them.

Tier	What you get	Typical price
`flex`	Spare capacity. Responses can queue for minutes, and requests can be refused when capacity runs out.	About 50% of standard
`priority` (alias `fast`)	Scheduled ahead of standard traffic: lower latency, faster output.	About 2x standard
`ultrafast`	OpenAI’s fastest tier, on selected models.	About 6x standard
`default`	The standard tier. Same as leaving the field out.	Standard

Request a tier

Add service_tier to the request body:

import os
from openai import OpenAI

client = OpenAI(
    base_url="https://api.opper.ai/v3/compat",
    api_key=os.environ["OPPER_API_KEY"],
)

resp = client.chat.completions.create(
    model="gpt-5.4-mini",
    service_tier="flex",
    messages=[{"role": "user", "content": "Summarize this report."}],
    timeout=600,  # flex requests can queue, allow a long timeout
)
print(resp.service_tier)  # "flex"

import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.opper.ai/v3/compat",
  apiKey: process.env.OPPER_API_KEY,
  timeout: 600_000, // flex requests can queue, allow a long timeout
});

const resp = await client.chat.completions.create({
  model: "gpt-5.4-mini",
  service_tier: "flex",
  messages: [{ role: "user", content: "Summarize this report." }],
});
console.log(resp.service_tier); // "flex"

curl https://api.opper.ai/v3/compat/chat/completions \
  -H "Authorization: Bearer $OPPER_API_KEY" \
  -H "Content-Type: application/json" \
  --max-time 600 \
  -d '{
    "model": "gpt-5.4-mini",
    "service_tier": "flex",
    "messages": [{ "role": "user", "content": "Summarize this report." }]
  }'

The field works on chat/completions, responses, openresponses and v1/messages. On v1/messages, Anthropic’s speed: "fast" is accepted too and means priority. auto, default, standard, standard_only and scale all mean the standard tier, so clients that send them (Codex does, for example) keep working. Any other value is a 400.

Or name the tier endpoint

Each tier is its own endpoint in the catalog, so you can also call it by id, with no service_tier field:

{"model": "openai:flex/gpt-5.4-mini", "messages": [...]}

Tier endpoint ids follow <provider>[:<location>]:<tier>/<model>, for example openai:priority/gpt-5.4, gemini:flex/gemini-3.8-flash or vertexai:eu:priority/gemini-3.6-flash. Tier endpoints are never picked for a request that doesn’t ask for a tier: calling gpt-5.4-mini without service_tier always runs at the standard tier.

What happens when the tier isn’t available

You ask for	Opper tries	If none answers
`flex`	the flex endpoint	the request fails (for example `429` or `503`). It never silently runs at the full price.
`priority`	the priority endpoint, then the standard one	standard is the fallback, billed at the standard price
`ultrafast`	ultrafast, then priority, then standard	standard is the fallback

If the model has no endpoint at the tier you asked for, the request runs at the standard tier and the response says default. Asking for flex never fails just because a model lacks it.

Fallbacks

Each tier is its own model id (openai:flex/gpt-5.4-mini), so it goes into your usual fallbacks like any other model:

The models array (Chat Completions): flex first, the same model at standard if flex has no capacity.

{
  "model": "openai:flex/gpt-5.4-mini",
  "models": ["openai/gpt-5.4-mini"],
  "messages": [...]
}

A dynamic route, on every endpoint: put both endpoints in a Pool ordered Cheapest first. The flex endpoint ranks first on price and the standard one takes over when flex is out of capacity.

Name the tier endpoints rather than setting service_tier in a chain: with service_tier set, every entry moves to its own tier endpoint when it has one (as on OpenAI and OpenRouter), so the fallback above would run on flex too.

See which tier served the request

You are billed at the tier that actually ran. Providers sometimes serve a priority request at the standard tier when they’re out of priority capacity; Opper reads that back from the provider and bills the standard price.

Header: X-Opper-Served-Service-Tier: flex | priority | ultrafast | default, on every response.
Body: service_tier on chat/completions, responses and openresponses when you asked for a tier or named a tier endpoint. Chat streams carry it on every chunk; meta.routing.served.service_tier names it too.
On a stream, the header is written before the provider confirms the tier, so treat the final chunk (or response.completed) as the authoritative answer.

Timeouts for flex

Flex requests can wait in the provider’s queue for minutes before the first token (Google quotes 1 to 15 minutes). Opper waits up to 10 minutes for the first token of a flex request instead of its usual first-token limit, so set your client timeout to at least 600 seconds. Use flex for background work: evaluations, enrichment, batch-like jobs that still need a synchronous answer.

Where tiers are available

Provider	Flex	Priority	Region
OpenAI	✓ (GPT-5 family, GPT-6, o3, o4-mini)	✓, and `ultrafast` on GPT-6 Astra	US
Google Gemini API	✓	✓	US
Google Vertex AI	✓ (global endpoint)	✓	Global, and EU for priority
xAI		✓ (every Grok text model)	US, and EU for the models served in the EU
Azure OpenAI		✓ (GPT-6 Sol, GPT-5.6 Sol and Terra)	Global
BytePlus	✓ (DeepSeek V4 Flash)		Asia-Pacific

To list the tier endpoints, look for the service_tier field in GET /v3/models, or open the Models page in the Opper platform, where tier endpoints carry a tier mark and their own price. The public catalog on opper.ai lists standard endpoints only.

Tier endpoints follow your compliance rules like any other endpoint. If your project only allows EU processing, OpenAI and Gemini API tiers are blocked; the Vertex AI and xAI EU priority endpoints are available.

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Service tiers

Request a tier

Or name the tier endpoint

What happens when the tier isn’t available

Fallbacks

See which tier served the request

Timeouts for flex

Where tiers are available

​Request a tier

​Or name the tier endpoint

​What happens when the tier isn’t available

​Fallbacks

​See which tier served the request

​Timeouts for flex

​Where tiers are available

Request a tier

Or name the tier endpoint

What happens when the tier isn’t available

Fallbacks

See which tier served the request

Timeouts for flex

Where tiers are available