AI Gateway: Empty Schema.version Fix For OpenAI Backends

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AI Gateway: Empty `schema.version` Fix for OpenAI Backends

Hey guys, ever run into a situation where your AI Gateway is adding an unwanted /v1 prefix to your API requests? Specifically, when you're trying to hook it up to an OpenAI-compatible backend that doesn't actually need that prefix? Yeah, it's a head-scratcher. Let's dive into a scenario where setting schema.version to an empty string ("") should mean no prefix, but it stubbornly defaults to v1. We'll explore why this happens and how to work around it, focusing on services like Perplexity AI that expect a clean /chat/completions endpoint.

The Problem: Unwanted /v1 Prefix

So, the main issue is that when you configure an AIServiceBackend with schema.name: OpenAI and schema.version: "" (an empty string), you'd expect the AI Gateway to forward requests to the upstream path without any version prefix. This means, for example, a request should go to /chat/completions. However, what's actually happening is that the AI Gateway's controller is converting that empty string into v1, resulting in requests being sent to /v1/chat/completions. This behavior contradicts the documentation's intent, especially when considering services like DeepSeek (and, importantly, Perplexity AI) that don't use a version prefix in their API endpoints.

According to the documentation, setting the version to an empty string should allow for omitting the prefix. However, it also states that it defaults to v1 if not set or empty. The expectation, especially when referencing the DeepSeek example, is that version: "" should result in /chat/completions, not /v1/chat/completions. This inconsistency causes problems when integrating with backends that don't adhere to the /v1/ convention.

In essence, the AI Gateway is designed to be flexible, accommodating different API schemas. Some, like the standard OpenAI setup, use versioned endpoints (e.g., /v1/chat/completions). Others, like Perplexity AI and DeepSeek, expect requests directly at the base endpoint (/chat/completions). The problem arises when the configuration doesn't accurately reflect the backend's requirements, leading to 404 errors and integration headaches.

This becomes a significant issue because it forces users to adapt their configurations to the AI Gateway's default behavior rather than the actual requirements of the AI service they are using. When integrating with services that diverge from the standard OpenAI structure, such as Perplexity AI, the unexpected v1 prefix leads to broken API calls and necessitates workarounds or modifications to the AI Gateway's internal logic.

Root Cause: cmp.Or Behavior in Gateway Controller

The root of the problem lies within the AI Gateway's internal controller, specifically in the internal/controller/gateway.go file, around line 158. The cmp.Or function is treating an empty string as a zero value and, as a result, is falling back to the default "v1". This prevents users from explicitly configuring the AI Gateway to work with OpenAI-compatible backends (like Perplexity AI) that don't expect or use a version prefix. This unintended behavior forces an incorrect URL structure, leading to failed API calls.

Essentially, the logic assumes that if a version isn't explicitly provided, it should default to the standard v1. While this is a reasonable default for many OpenAI-compatible services, it breaks compatibility with those that intentionally omit the version prefix. The cmp.Or function, in this context, is too aggressive in its interpretation of an empty string, preventing the desired behavior of sending requests to the base endpoint.

This default behavior is particularly problematic because it's not immediately obvious to users. They might reasonably expect that setting version: "" would disable the version prefix, only to find that the AI Gateway is silently adding it back in. This lack of transparency can lead to confusion and wasted time as users debug their configurations.

Reproducing the Issue: Step-by-Step

Okay, let's walk through the steps to reproduce this behavior. This will give you a clear understanding of the problem and allow you to verify the fix once it's implemented.

  1. Create an AIServiceBackend with an empty version:

First, you'll define an AIServiceBackend resource. This resource tells the AI Gateway how to connect to your chosen AI service. The key part here is setting the schema.version to an empty string.

apiVersion: aigateway.envoyproxy.io/v1alpha1
kind: AIServiceBackend
metadata:
  name: perplexity
  namespace: envoy-ai-gateway-system
spec:
  schema:
    name: OpenAI
    version: ""
  backendRef:
    name: perplexity-backend
    kind: Backend
    group: gateway.envoyproxy.io
  1. Create a Backend pointing to api.perplexity.ai:

Next, you need a Backend resource. This resource defines the actual endpoint where the AI service is located. In this case, we're pointing it to Perplexity AI's API.

apiVersion: gateway.envoyproxy.io/v1alpha1
kind: Backend
metadata:
  name: perplexity-backend
  namespace: envoy-ai-gateway-system
spec:
  endpoints:
    - fqdn:
        hostname: api.perplexity.ai
        port: 443
  1. Create an AIGatewayRoute to route requests:

Now, you need to create an AIGatewayRoute. This resource defines how incoming requests are routed to the correct backend based on certain criteria (in this case, the x-ai-eg-model header).

apiVersion: aigateway.envoyproxy.io/v1alpha1
kind: AIGatewayRoute
metadata:
  name: perplexity-route
  namespace: envoy-ai-gateway-system
spec:
  parentRefs:
    - name: my-gateway
      namespace: envoy-ai-gateway-system
      kind: Gateway
      group: gateway.networking.k8s.io
  filterConfig:
    type: ExternalProcessor
  rules:
    - matches:
        - headers:
            - type: RegularExpression
              name: x-ai-eg-model
              value: "sonar.*"
      backendRefs:
        - name: perplexity
  1. Send a request:

Finally, send a POST request to your gateway's /chat/completions endpoint. Make sure to include the necessary headers, like your Authorization token and Content-Type.

curl -X POST https://your-gateway/v1/chat/completions \
  -H "Authorization: Bearer your-key" \
  -H "Content-Type: application/json" \
  -d '{"model": "sonar-pro", "messages": [{"role": "user", "content": "Hello"}]}'

Expected Behavior: The gateway should forward the request to https://api.perplexity.ai/chat/completions.

Actual Behavior: The gateway incorrectly forwards the request to https://api.perplexity.ai/v1/chat/completions, resulting in a 404 error because that endpoint doesn't exist.

Expected Behavior vs. Actual Behavior

To reiterate, the expected behavior is that when schema.version is set to an empty string, the AI Gateway should forward requests to the base endpoint /chat/completions without adding any version prefix. This is crucial for compatibility with services like Perplexity AI that expect requests at this specific endpoint.

However, the actual behavior is that the AI Gateway, due to the cmp.Or logic, injects the /v1 prefix, sending requests to /v1/chat/completions. This leads to a 404 error because Perplexity AI (and similar services) do not have a /v1/chat/completions endpoint. This discrepancy highlights the core problem: the AI Gateway's interpretation of an empty schema.version is not aligned with the requirements of certain OpenAI-compatible backends.

This issue can have a significant impact on users attempting to integrate with these services, as it requires them to either modify the AI Gateway's internal code or find other workarounds to remove the unwanted version prefix. The unexpected behavior can also lead to confusion and frustration, as users may not immediately understand why their requests are failing.

Impact and Next Steps

This issue directly impacts anyone using, or planning to use, an OpenAI-compatible backend that doesn't use a version prefix in its API endpoint. It forces you to either modify the AI Gateway's code or find hacky workarounds. Addressing this requires modifying the controller logic to correctly handle the empty string case for schema.version. Specifically, the cmp.Or function should be adjusted to allow an empty string to signify no version prefix, enabling seamless integration with services like Perplexity AI and DeepSeek. By resolving this, the AI Gateway becomes more flexible and truly compatible with a wider range of AI service providers.

By fixing this issue, the AI Gateway will become more versatile and user-friendly, allowing for seamless integration with a broader range of AI services. This will reduce the need for custom workarounds and ensure that the AI Gateway behaves as expected, regardless of the specific API schema used by the backend.