A Free Model Endpoint Needs a Cold-Start Budget

A free model endpoint is only trustworthy when you can separate server warm-up from model behavior.

The trap: free server options remove cost but add cold starts, route changes, and retries. A slow first response looks like a bad model. It may only be a cold instance.

Measure four fields:

• total request time
• response model
• request ID
• status code or retry pattern

Disclosure: This article was prepared as part of MonkeyCode's product outreach. MonkeyCode's free model access and free server option are useful here because they make cold starts visible without a credit card. The probe below works with any OpenAI-compatible endpoint.

Reproducible probe

import time
import requests

ENDPOINT = 'https://your-endpoint/v1/chat/completions'
API_KEY = 'your-key'
PAYLOAD = {
    'model': 'model-you-chose',
    'messages': [{'role': 'user', 'content': 'Return exactly: ok'}],
    'max_tokens': 5,
}

def call(label):
    t0 = time.monotonic()
    r = requests.post(
        ENDPOINT,
        headers={'Authorization': f'Bearer {API_KEY}'},
        json=PAYLOAD,
        timeout=30,
    )
    r.raise_for_status()
    total = time.monotonic() - t0
    body = r.json()
    model = body.get('model')
    req_id = body.get('id') or r.headers.get('x-request-id')
    text = body['choices'][0]['message']['content']
    print(f'{label} total={total:.3f}s model={model} req={req_id} text={text!r}')
    return total

# cold: idle gaps, expect possible start-up cost
for i in range(3):
    call(f'cold-{i}')
    time.sleep(20)

# warm: back-to-back, expect less variance
for i in range(5):
    call(f'warm-{i}')

Read it

Build a small table:

Sample	p50	p95
cold	2.10s	4.80s
warm	0.65s	1.10s

Example numbers only. Your medians depend on region, model, and free-tier routing.

What to conclude:

• Different model across calls: route drift, not model drift.
• Same model, different req_id pattern: possible retries or load balancer changes.
• Cold p50 close to warm p50: endpoint is stable enough for quick eval.
• Cold p95 far from warm p95: do not compare model outputs from mixed samples.

Limitations

• Cold start is outside your control.
• A single day of measurements is not a guarantee.
• Network noise from your machine affects total time.
• Free tiers may throttle, queue, or route to different regions.
• This measures serving, not model quality.

Who should skip this

• You have a strict SLO or production workload.
• You only compare model quality and plan to call long-running jobs.
• You need stable latency over hours or days.
• You cannot tolerate rate limits or route changes.

If you run it, record p50 and p95 before trusting any eval.