API Latency Test | AI API Speed, P95 Latency and TTFT Check
Run AI API latency tests for OpenAI, Claude, Gemini and relays: P50/P95/P99, TTFT, streaming speed and 429 rate limits.
Quick Answer
An API latency test should not only measure average time. AIBench separates end-to-end P50/P95/P99, streaming TTFT, chunk interval and rate-limit signals to show real product responsiveness and stability.
How It Works
- 1Send multiple requests with the same model and prompt.
- 2Record non-streaming end-to-end latency and streaming TTFT separately.
- 3Calculate P50/P95/P99 to identify tail latency and jitter.
- 4Combine 429, 5xx and success rate to judge stability.
Use Cases
- Compare first-token speed across API channels.
- Investigate slow chat responses.
- Choose low-tail-latency channels for agent workflows.
- Monitor API jitter and rate limits after launch.
Core Metrics
P50
Typical request latency
P95
Tail latency and stability
TTFT
First streamed content chunk
Success rate
Whether requests finish reliably
Why TTFT matches user perception
In chat products, users feel the system is responding once the first token appears. TTFT often explains perceived speed better than full generation time.
Why P95 matters
User experience is shaped by slow requests. P95 reveals queueing, gateway congestion, rate limits and cross-region network jitter better than averages.
Related Search Terms
FAQ
How many requests should an API latency test run?
A quick check can start with a small sample. Procurement or SLA decisions should use fixed regions, fixed prompts, larger samples and repeated time windows.
Is TTFT or P95 more important?
Chat apps care more about TTFT and stream stability; batch jobs care more about end-to-end P95/P99 and success rate.
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