CometAPI chat completions: reliability contract checks

Last reviewed: 2026-05-08

Who this is for: engineers operating production LLM clients that call CometAPI chat completions and need to know exactly when to retry, fail closed, fall back, or alert.

For broader reliability patterns, see the site index at /sites/llm-api-reliability/ and related playbooks under /sites/llm-api-reliability/posts/. Editorial assumptions for this site are tracked at /sites/llm-api-reliability/editorial/.

Key takeaways

• Treat the CometAPI chat completions API reference as the boundary contract, not as a full production-readiness plan.
• Verify endpoint path, auth headers, required request fields, response shape, and failure behavior with live contract tests before routing production traffic.
• Do not hard-code unsupported assumptions about pricing, available models, latency, quota, or rate-limit thresholds from this draft.
• Classify failures by operator action: fix request, refresh credentials, retry briefly, fall back, or page.
• Keep fallback thresholds as tunable examples. Your timeout, retry, and failover policy should reflect user experience budgets and contractual limits.
• Save sanitized request and response fixtures so contract drift is visible before it reaches users.

Concise definition

A chat completions reliability contract is the minimum behavior your client depends on at the API boundary: the endpoint it calls, headers it sends, request fields it must provide, response fields it parses, errors it classifies, and retry or fallback actions it takes when the call does not complete as expected.

The supplied source for this draft is the CometAPI API documentation page for the chat completions endpoint: https://apidoc.cometapi.com/api-13851472.

Contract details to verify

Use this table as an implementation checklist. The “operator stance” column is intentionally conservative: if the supplied documentation does not prove a behavior, validate it in your own tenant before relying on it.

Failure-mode checklist

1. Pin the contract you are testing

Record these values in your runbook before the first test:

• Documentation URL: https://apidoc.cometapi.com/api-13851472
• Access date: 2026-05-08
• API base URL used by your environment
• Chat completions path used by your client
• Auth method and secret source
• Model identifier used for the test
• Whether streaming is enabled
• Client timeout values
• Retry and fallback policy version

The goal is not just to prove that one request worked. The goal is to make later drift obvious.

2. Run a minimal happy-path test

Use a deterministic, low-token prompt that does not include sensitive data. Replace placeholders with values verified from the CometAPI documentation and your tenant configuration.

curl -sS -X POST "$COMETAPI_BASE_URL/v1/chat/completions" \
  -H "Authorization: Bearer $COMETAPI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "your-verified-model-id",
    "messages": [
      {
        "role": "system",
        "content": "Return JSON only."
      },
      {
        "role": "user",
        "content": "Return {\"status\":\"ok\"}."
      }
    ],
    "temperature": 0,
    "max_tokens": 20
  }'

Validation points:

• HTTP status is successful.
• Response body is valid JSON.
• At least one choice is present, if the documented response shape uses choices.
• Assistant content can be extracted without special-case parsing.
• Finish reason is captured if returned.
• Usage data is captured if returned and documented.
• The raw response is stored as a sanitized fixture.

Do not assert that the model returns the exact same text forever. For reliability tests, assert transport, schema, and parseability first.

3. Test malformed request handling

Send controlled bad requests from a non-production key or isolated environment. Keep volume low.

Recommended cases:

Your client should not fall back to another provider for errors caused by its own invalid request shape. Fallback can hide bugs and increase cost.

4. Test timeout and retry boundaries

Choose timeouts from your product’s user experience budget, not from generic advice. A practical pattern is:

• Short connect timeout.
• Overall request deadline.
• One or two bounded retries only for clearly transient failures.
• No retry for malformed requests or auth failures.
• Fallback only if the remaining user deadline can still produce a useful answer.

Example classification to tune:

5. Validate streaming separately if you use it

Streaming is a different contract from non-streaming completion. If your request includes a streaming flag documented by CometAPI, test these behaviors separately:

• First-byte latency is recorded.
• Each event or chunk parses without blocking the consumer.
• Partial content is buffered safely.
• The terminal event or connection close is handled consistently.
• Mid-stream disconnect does not produce an unmarked “successful” answer.
• Retries after partial streaming are either disabled or clearly marked as regenerated output.

For user-facing systems, the dangerous state is not “request failed.” The dangerous state is “partial answer looked complete.”

6. Capture observability fields

At minimum, log these fields with prompt content redacted or summarized:

• Client-generated request id.
• Environment and service name.
• Endpoint path and API base URL alias, not secret-bearing full URLs.
• Model identifier.
• Streaming flag.
• HTTP status.
• Error class.
• Retry count.
• Fallback provider or fallback model, if used.
• Total latency.
• First-token latency for streaming, if measured.
• Finish reason, if returned.
• Usage fields, if returned.
• Parser outcome: success, invalid JSON, missing field, empty content, timeout.

Avoid logging API keys, full user prompts, regulated data, or unredacted responses.

Suggested acceptance criteria

A CometAPI chat completions client is ready for controlled production traffic when all of these are true:

• The endpoint and auth contract match the current CometAPI API reference.
• A minimal completion succeeds from the production runtime environment.
• Malformed requests fail as non-retryable client errors.
• Auth failures do not trigger fallback.
• Retry logic is bounded and has jitter.
• Fallback only runs when the request is safe to reissue and the user deadline still allows it.
• The parser tolerates extra response fields and rejects missing required fields.
• Streaming and non-streaming paths have separate tests if both are used.
• Runbooks say who owns credential, model, quota, and billing failures.
• Sanitized fixtures are checked into the reliability test suite.

FAQ

Is this the same as a smoke test?

No. A smoke test proves that one basic request can complete. A reliability contract test proves what your client does when the request is malformed, unauthorized, throttled, timed out, partially streamed, or returned with a schema your parser did not expect.

Should every 5xx response trigger fallback?

Not automatically. A retry or fallback should respect the caller’s deadline, idempotency risk, and cost controls. For a normal chat answer, retrying may be acceptable. For workflows that trigger external actions, duplicate generation may create operational risk.

Should auth failures fall back to another provider?

Usually no. Auth failures indicate configuration, secret rotation, permission, or account state problems. Falling back can mask the incident and make debugging harder. Alert the owner instead.

Can I rely on fixed rate limits from this article?

No. The supplied evidence URL is the CometAPI API reference, not a tenant-specific quota or billing document. Verify rate limits, quota windows, and billing behavior from your account materials or vendor support.

What response fields should my parser require?

Require only the fields your application truly needs and that the CometAPI reference documents for the response mode you use. Treat optional telemetry fields, such as usage or request ids, as optional unless your source contract says otherwise.

How often should these checks run?

Run the happy-path contract test continuously or on a short schedule. Run the destructive or malformed-request cases before release, after SDK changes, after credential rotation, after model configuration changes, and when the CometAPI reference changes.

Sources checked