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

Together AI hosts hundreds of open models on shared capacity, and that architecture shows up directly in its error codes: the failure you will actually spend time on is not a bad request, it is a model that is temporarily oversubscribed.

The single most expensive mistake in Together AI integrations is treating every non-200 the same way: one generic catch block, one blind retry loop. Half of Together AI'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 Together AI API Error Code

Codes below are what Together AI 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 Together AI Error That Wastes the Most Time

Together AI's signature error is model overload — a 429 or 503 whose body says the model, not your key, is out of headroom. Because capacity is pooled per model, the fix is orthogonal to everything you would try for a normal quota error: switching to a different model size or a Turbo/Lite variant of the same family clears it instantly, while backoff on the original model can stall for minutes. Read the message body, not just the status code, before deciding which lever to pull.

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, 403, 404]);

async function callTogetherAi(body, attempt = 0) {
  const res = await fetch('https://api.together.xyz/v1/chat/completions', {
    method: 'POST',
    headers: { 'Authorization': `Bearer ${process.env.TOGETHER_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(`Together AI error ${res.status} (not retryable): ${detail}`);
  }

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

  if (attempt >= 4) throw new Error(`Together AI 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 callTogetherAi(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 Together AI. Nothing else in this list matters if you skip this step.
2. Log the response body. Together AI 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.together.ai and live Together AI monitoring for a confirmed incident before rolling back your own deploy.

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

Where to Send Traffic When Together AI 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 Together AI 503 does not follow you there.

Frequently Asked Questions

Related Together AI Guides

• Is Together AI Down? Outage Checking Guide
• Together AI API Rate Limits Explained
• Together AI API Monitoring Guide
• Groq vs Together AI
• API Error Handling: The Complete Guide
• API Rate Limiting: The Complete Guide