Cohere API Error Codes Explained: 400, 401, 429, 5xx and Fixes

Cohere ships two things most inference APIs do not: a hard split between trial and production keys, and a dedicated status code for content it refuses to process. Both produce errors that look like bugs until you know what they are.

The single most expensive mistake in Cohere integrations is treating every non-200 the same way: one generic catch block, one blind retry loop. Half of Cohere's error codes are deterministic — retrying them cannot succeed, it only burns quota and hides the real cause. This guide splits them into the ones you fix, the ones you wait out, and the ones you fail over on.

Every Cohere API Error Code

Codes below are what Cohere returns in production today. Response shapes drift as APIs version, so log the full body — the message text usually names the failing field, and that detail is what turns a 20-minute debug into a 20-second one.

The Cohere Error That Wastes the Most Time

Cohere's trial-versus-production key split causes more confused debugging than any genuine fault. A trial key is free and permanent, but capped at a very low request rate and barred from production use — so the same code that passes in development starts returning 429 the moment real traffic hits it, with nothing in the error text saying "you are on a trial key." Before you engineer any backoff strategy, check which key class you are holding in the Cohere dashboard.

Retry or Don't: The Decision Table

This is the part most error handling gets wrong. Retrying a deterministic error is strictly worse than failing fast — it delays the real signal and, on paid tiers, multiplies the bill.

Error Handling That Distinguishes All Three

One handler, three behaviours. The important line is the one that does not retry.

const FATAL = new Set([400, 401, 402, 404, 498, 499]);

async function callCohere(body, attempt = 0) {
  const res = await fetch('https://api.cohere.com/v2/chat', {
    method: 'POST',
    headers: { 'Authorization': `Bearer ${process.env.COHERE_API_KEY}`, 'Content-Type': 'application/json' },
    body: JSON.stringify(body),
  });

  if (res.ok) return res.json();

  // Log the body once — it names the failing field on every 4xx
  const detail = await res.text();

  if (FATAL.has(res.status)) {
    throw new Error(`Cohere error ${res.status} (not retryable): ${detail}`);
  }

  if (res.status >= 500) {
    // Cohere-side: fail over rather than queue behind an outage
    if (attempt >= 1) return callFallbackProvider(body);
  }

  if (attempt >= 4) throw new Error(`Cohere failed after retries: ${detail}`);

  const retryAfter = Number(res.headers.get('retry-after')) || 0;
  const backoff = retryAfter * 1000 || (2 ** attempt) * 500 + Math.random() * 500;
  await new Promise((r) => setTimeout(r, backoff));
  return callCohere(body, attempt + 1);
}

Note the fallback triggers on the second 5xx, not the first. A single 500 is often a one-off on a single host; two in a row is an incident, and that is the point where switching providers beats waiting.

Your Error or Theirs? A 60-Second Check

1. Read the status class. 4xx is you, 5xx is Cohere. Nothing else in this list matters if you skip this step.
2. Log the response body. Cohere names the offending field or model in the message — the status code alone is rarely enough.
3. Try a second API key. If a different key on a different account works, the problem is your account state or quota.
4. Try a different model. A working sibling model rules out an infrastructure-wide incident and points at naming, context length, or per-model capacity.
5. Check status.cohere.com and live Cohere monitoring for a confirmed incident before rolling back your own deploy.

For the outage-side playbook, see our Is Cohere Down? guide. For quota specifically, the Cohere rate limit guide covers headers and tier ceilings in depth.

Where to Send Traffic When Cohere Returns 5xx

Fallbacks only help if they are configured before the incident. Each of these runs on independent infrastructure and an independent quota pool, so a Cohere 503 does not follow you there.

Frequently Asked Questions

Related Cohere Guides

• Is Cohere Down? Outage Checking Guide
• Cohere API Rate Limits Explained
• Cohere API Monitoring Guide
• Mistral vs Cohere
• API Error Handling: The Complete Guide
• API Rate Limiting: The Complete Guide