Hey everyone,
Running into a weird billing issue with AI Gateway and figured I'd check if anyone else has hit this.
I'm calling openai/gpt-5.5 through the OpenAI-compatible endpoint with service_tier: "flex" set on every request. In the request logs, the response actually comes back with service_tier: "flex" confirmed, so the model is processing under flex tier as expected.
The problem: the usage logs and invoice line items are billing those same requests at standard tier pricing, not the 50% flex rate.
So basically:
- Request: service_tier: "flex"
- Response: service_tier: "flex" ✓
- Billing: standard rate ✗
Has anyone else seen this with GPT-5.5, or any of the GPT-5 family? Wondering if this is a known issue with the pricing engine ignoring the tier that the model returned, or if there's something else I'm supposed to set on my side.
Already filed a support ticket, but posting here too in case others are getting silently overcharged.
My log<<
], "usage": { "prompt_tokens": 37685, "completion_tokens": 3746, "total_tokens": 41431, "cost": 0.288133, "is_byok": false, "prompt_tokens_details": { "cached_tokens": 2816, "audio_tokens": 0, "video_tokens": 0 }, "cost_details": { "upstream_inference_cost": null, "upstream_inference_prompt_cost": 0, "upstream_inference_completions_cost": 0 }, "completion_tokens_details": { "reasoning_tokens": 1552, "image_tokens": 0 }, "cache_creation_input_tokens": 0, "market_cost": 0.288133 }, "system_fingerprint": "fddddddddd", "service_tier": "flex", "generationId": "Say something"}