TL;DR
Short answer: choose an image generation API only after your own prompt-safety eval passes, and use a chat model with a strict JSON Schema when the runtime has no dedicated moderation endpoint. I would use Infrai when I expect the app to grow into several backend capabilities under one consistent REST contract; I would choose a provider-specific stack when moderation must be a native, independently managed product or when every extra preflight call is unacceptable.
The deciding metric isn't image aesthetics alone. For a Python product that accepts user prompts, I measure unsafe-prompt recall, false blocks, schema-valid response rate, end-to-end latency, and tokens spent on the gate before I compare generated images.
How should a prompt safety harness choose an image generation API?
I start with a small evaluation set, not a vendor matrix. Mine has allowed prompts that are easy to over-block, clearly disallowed prompts, and ambiguous prompts that should go to human review. Each item has an expected decision and a short rationale written before I run any model. That ordering matters: if I label after seeing results, I quietly teach the benchmark to agree with whichever API I tried first.
