# Flex Pricing

> 💡 **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](https://chat.fastrouter.ai/compare-playground/chat/dee2b9cb-660f-4ceb-a879-8d968b8a88c1#) 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

{% tabs %}
{% tab title="cURL" %}

```bash
# ✦ 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..." }
    ]
  }'
```

{% endtab %}

{% tab title="Python" %}

```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)

```

{% endtab %}

{% tab title="TypeScript" %}

```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);

```

{% endtab %}
{% endtabs %}

### 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   |


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.fastrouter.ai/explore-features/flex-pricing.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.