I'm building a low-latency AI feature, which API is best

If your priority is low latency, the “best” API depends mainly on what kind of AI feature you’re building:

Best general choice for low latency

• OpenAI Responses API with a smaller/faster model is usually the safest default for real-time UX.
• For chat/autocomplete/classification, pick the fastest available model rather than the largest one.

If you need the absolute lowest latency

Consider these options:

• Smaller models over frontier models
• Streaming responses so users see tokens immediately
• Short prompts / trimmed context
• Prompt caching if your requests share a stable prefix
• Batching only if throughput matters more than per-request latency

Practical recommendation

• Interactive user-facing app: use a fast OpenAI model via Responses API + streaming
• High-QPS backend classification/extraction: use a small model, minimal context, possibly a fine-tuned or distilled model if available
• If latency is extremely critical and fixed: a self-hosted small open-source model on dedicated infra may beat hosted APIs, but adds ops complexity

What matters most for latency

1. Model size
2. Input length
3. Output length
4. Network distance
5. Streaming support
6. Concurrency / rate limits

If you tell me:

• your use case,
• target latency,
• expected input/output size,
• and whether you need text, vision, or function calling,

I can recommend a specific API/model setup.