Flex Pricing

Access OpenAI and Google Gemini models at up to 50% lower cost by opting into flexible inference — ideal for background tasks, batch workloads, and latency-tolerant applications.

💡 Instant savings, zero code changes Append :flex to any supported model ID. Your API key, endpoint, and payload stay exactly the same.

What is Flex Pricing?

Flex inference is a tiered pricing mode offered by OpenAI and Google on select models. When you use the :flex suffix, FastRouter routes your request to the provider's Flex tier — significantly reducing token costs in exchange for variable throughput and potentially higher latency under peak load.

Flex is well-suited for workloads that don't require guaranteed low latency: data extraction pipelines, classification jobs, offline summarisation, evals runs, and other async or background tasks.

⚠️ Not recommended for real-time user-facing responses Flex requests may experience higher tail latencies during peak provider load. Use the standard tier for interactive or streaming use-cases.

Pricing Comparison

Example using GPT-5.4 Nano via the OpenAI provider:

Tier	Input	Output	Blended	Context
Standard	$0.20 / 1M tokens	$1.25 / 1M tokens	$0.46 / 1M tokens	400,000
✦ Flex	$0.10 / 1M tokens	$0.63 / 1M tokens	—	400,000

↓ ~50% savings on tokens

Actual savings vary by model. Check the model catalog for per-model Flex pricing across all supported providers.

Supported Providers

Flex pricing is currently available on the following providers:

Supported Provider
OpenAI
Gemini API on Vertex AI and AI Studio

How to Use Flex

1. Identify a Flex-supported model Check the model catalog for the Flex tab in Provider Details. If the tab is present, Flex pricing is available for that model.

2. Append :flex to the model ID Change your model field from openai/gpt-5.4-nano to openai/gpt-5.4-nano:flex or from google/gemini-3.1-pro-preview to google/gemini-3.1-pro-preview:flex That's the only change required.

3. Optionally pin the provider Use "provider": {"only": ["openai"]} or "provider": {"only": ["googleaistudio"]} or "provider": {"only": ["googlevertexai"]} to ensure the request goes to the correct provider for the Flex tier and isn't rerouted.

Code Examples

cURL

# ✦ With Flex — ~50% cheaper
curl 'https://api.fastrouter.ai/api/v1/chat/completions' \
  --header 'Authorization: Bearer YOUR_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{
    "model": "openai/gpt-5.4-nano:flex",
    "provider": { "only": ["openai"] },
    "messages": [
      { "role": "user", "content": "Summarise this document..." }
    ]
  }'

Python

from openai import OpenAI

client = OpenAI(
    base_url="https://api.fastrouter.ai/api/v1",
    api_key="YOUR_API_KEY",
)

response = client.chat.completions.create(
    model="openai/gpt-5.4-nano:flex",
    extra_body={"provider": {"only": ["openai"]}},
    messages=[
        {"role": "user", "content": "Summarise this document..."}
    ],
)

print(response.choices[0].message.content)

TypeScript

import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.fastrouter.ai/api/v1",
  apiKey: process.env.FASTROUTER_API_KEY,
});

const response = await client.chat.completions.create({
  model: "openai/gpt-5.4-nano:flex",
  // @ts-expect-error - FastRouter routing extension
  provider: { only: ["openai"] },
  messages: [
    { role: "user", content: "Summarise this document..." },
  ],
});

console.log(response.choices[0].message.content);

When to Use Flex

Use Flex ✦	Use Standard
Data extraction & classification pipelines	Real-time chat & interactive UIs
Batch document summarisation	Streaming responses to end users
Eval or fine-tuning dataset generation	Latency-sensitive agent loops
Scheduled background jobs	Voice or real-time applications
Cost-optimised preprocessing at scale	SLA-bound enterprise workflows