Who can use this feature: Anyone on any plan.

This feature is currently in beta. While you’re welcome to try it out, please know that our team is still working to refine it. Your feedback is valuable to help us improve!


Given the instability of some APIs and the multitude of similar providers, we have developed a unified gateway that acts as a single endpoint for accessing multiple APIs.

Why Gateway Fallbacks

Instead of using the Helicone-Target-Url header to send requests to a specific API, you can use this unified gateway to:

  • Automatically switch to fallback options in case of an API failure or error response.
  • Eliminate the need to modify your code when switching providers.
  • Maintain high availability and reliability in critical applications that depend on external APIs.

Getting Started

To get started, add the header Helicone-Fallbacks to your request.

This header should contain a JSON string dump of the fallbacks you wish to use. The fallbacks are prioritized, meaning the first one will be used if available. If it is not available, the system will attempt to use the next one, and so on.

The header is structured as follows:

export type HeliconeFallbackCode = number | { from: number; to: number };

export type HeliconeFallback = {
  "target-url": string;
  headers: Record<string, string>;
  onCodes: HeliconeFallbackCode[];
  bodyKeyOverride?: object;

Extracting Fallbacks Response Header

When fallbacks is enabled, you can capture the fallback index from the headers of the response returned.

Helicone-Fallback-Index: number // indicates the fallback  used.


Using the OpenAI API and set LemonFox API as fallback, then extracting the header.

For integration with other languages, please refer to the format in Header Directory.

Python (w/o package)
url = "https://gateway.helicone.ai/v1/chat/completions"

headers = {
  "Content-Type": "application/json",
  "Helicone-Auth": "Bearer <Helicone KEY>",
  "Helicone-Fallbacks": json.dumps([ # add this new header
      {   # this API will be used if available, otherwise, the system will use the next one
          "target-url": "https://api.openai.com",
          "headers": {
            "Authorization": "Bearer <OpenAI Key>",
          "onCodes": [{"from": 400, "to": 500}]
      {   # set fallback to LemonFox API
          "target-url": "https://api.lemonfox.ai",
          "headers": {
              "Authorization": "Bearer <LemonFox Key>",
              "Content-Type": "application/json",
          "onCodes": [401, 403],
          "bodyKeyOverride": {
              "model": "zephyr-chat",
payload = {
  "model": "gpt-4",
  "messages": [
      "role": "user",
      "content": "What is the meaning of life?"
  "max_tokens": 300

response = requests.post(url, headers=headers, data=json.dumps(payload))
print("Fallback index used: ", response.headers["helicone-fallback-index"])


Using Approved Domains

Helicone supports integration with several approved domains for providers such as OpenAI, Anthropic, Together-AI, OpenRouter, and Azure.

Choosing from our latest list of approved domains as fallbacks means you can send unlimited requests to the providers via Helicone.

Using Unapproved Domains

You can also use unapproved domains as fallbacks. However, to protect our community from potential threats, we have certain restrictions for unapproved domains:

  • 10,000 requests per day
  • 1 request per second


Questions or feedback? Reach out to help@helicone.ai or schedule a call with us.