Together AI API 401 Unauthorized: Every Cause, in the Order Worth Checking (2026)

A 401 is the earliest possible refusal. The connection succeeded, TLS completed, the request reached Together AI — and it was rejected before anything in the body was parsed. Your model id was never checked. Your parameters were never validated. Your usage was never consulted. Everything you would normally inspect when a call fails is downstream of the point at which this one stopped.

That is what makes it the fastest error in the catalogue to fix and the easiest to misdiagnose. Teams reach for the payload, the SDK version and the status page, when the entire fault surface is one string and how it travelled. The six causes below are ordered by how often they turn out to be the answer, and the first two account for most of them.

30-second triage: run the same call with curl from your own machine using the key you believe production is holding. If curl succeeds, the credential is valid and the problem is how your application resolves it — not the key, not Together AI. If curl fails too, the credential itself is dead and you are looking for a rotation, a revocation or an account state. Check live Together AI status only if both a known-good key and a fresh one are refused.

401, 403 and 429 are three different problems with three different owners

These get filed together as “the API rejected us” and handled by one branch in a client, which is how a credential problem ends up in a retry loop and a permission problem ends up in a secret rotation. The distinction is about which question the service refused to answer.

	401 Unauthorized	403 Forbidden	429 Too Many Requests
What was refused	Who you are	What this identity may do	How much you asked for
Does retrying help?	Never — it is deterministic	Never	Yes, after a backoff
Who fixes it	An engineer with secret-store access	An account administrator	Whoever controls client pacing
Does failover help?	No — your secret travels with you	No	It exports your pacing bug
Counts as Together AI downtime?	Never	Never	Never

The row that costs the most time is the second one. A client that applies one retry policy to all 4xx responses will hammer a deterministic refusal until its deadline expires, turning an error that could have been surfaced in milliseconds into a request that hangs for the full retry budget. The throttling case is genuinely different and is covered in the Together AI 429 guide.

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Read the raw response, not the SDK exception

Most SDKs collapse an auth failure into a generic exception class and a message that has been through two layers of wrapping. The status code survives; the body, which is where the provider explains which of the six causes applies, frequently does not. Reproduce the call at the wire level before you form a theory:

curl -i -s -X POST https://api.together.xyz/v1/chat/completions \
  -H "Authorization: Bearer $TOGETHER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"meta-llama/Llama-3.3-70B-Instruct-Turbo","messages":[{"role":"user","content":"ping"}],"max_tokens":1}'

# Confirm the shell is holding what you think it is holding - never print the key:
echo "len=${#TOGETHER_API_KEY} prefix=${TOGETHER_API_KEY:0:4}"

That second line resolves more 401s than any amount of reading client code. It answers two questions at once: whether the variable is set at all in this context, and whether the value has an unexpected length — the signature of a trailing newline or a truncated copy-paste. Print the same two facts at application startup and the next occurrence is diagnosed from a boot log rather than a reproduction.

The Together AI trap: a marketplace refuses per model, and only some of those refusals are 401s

On a single-vendor API, a credential either works or it does not. On a marketplace it is more granular: the account is authenticated once, and then each model is separately gated by licence acceptance, availability and in some cases a dedicated deployment. That means a key which is unambiguously valid can still fail a request — and the status code tells you which kind of failure you have. Reading every auth-shaped error as “bad key” sends you rotating a credential that was never at fault.

The practical consequence is that a fallback chain across model ids is the most common way to discover this. The primary model works, an incident pushes traffic to the alternate, and the alternate has never been granted to this account — so a resilience mechanism designed to survive a failure introduces one. Exercise every branch of a fallback chain with a synthetic call on a schedule, not only when the primary is already broken. An untested fallback is not a fallback.

The third Together-specific cause is environment drift across the OpenAI-compatible surface. Because the endpoint accepts an OpenAI-shaped client with the base URL overridden, a process that also talks to OpenAI can resolve the wrong credential from ambient environment and send it here. Pass the key explicitly to each client constructor rather than letting any SDK infer it, and this whole category stops existing.

The six causes, in the order worth checking

Work down this list rather than across it. Each step is cheap, and the ordering reflects which answers turn out to be correct most often rather than which are most interesting.

The wrong provider credential was resolved from the environment. The OpenAI-compatible surface makes a default credential lookup dangerous. Pass the key explicitly per client.
A fallback model id was never granted to this account. The credential is valid; the model is not available to it. That refusal is usually a 403, not a 401 — read the code, not the shape.
The key was rotated and only some hosts got the new one. A partial rollout produces a 401 rate that is a clean fraction of traffic. That ratio is the diagnosis.
Whitespace or a newline rode along with the secret. A key read from a file or piped through a shell frequently carries a trailing newline. The header becomes invalid and the value still looks perfect in a dashboard.
The header was built by hand and lost the scheme. Together expects Authorization: Bearer <key>. Sending the bare key is a 401 with a valid credential inside it.
A proxy stripped or rewrote the Authorization header. Corporate egress proxies and some service meshes drop inbound auth headers by policy. The 401 you are reading was never emitted by Together AI.

Notice what is absent from that list: anything about your request body, your model choice or your traffic volume. If you find yourself editing a prompt or lowering concurrency in response to a 401, you have left the fault surface entirely. The complete map of which code means what is in the Together AI API error codes reference.

Make the next one impossible instead of fast

A 401 is a five-minute fix that recurs forever unless the conditions that produced it change. Three structural changes remove most of the category permanently, and none of them are about the key itself:

Rotate with an overlap window. Issue, roll, verify from every environment, then revoke. An atomic rotation guarantees a failure window whose length is your deploy time. The sequence is in the Together AI key rotation guide.
Read the secret at request time, not at import time. A credential cached in a module-level constant at process start cannot be updated without a restart, which is why rotations turn into deploys and deploys turn into windows.
Pass the key explicitly to every client. Ambient resolution from environment variables is convenient in a single-provider process and a liability in any process that talks to two, because the wrong credential is a valid one belonging to somebody else.
Synthetically exercise every credential you hold. A key used only by a fallback path or a monthly batch job is a key you will discover is dead at the moment you need it. A one-request-per-hour probe per credential turns that into a Tuesday-morning ticket.
Alert on auth failures separately from availability. A 401 rolled into a general error-rate alert either pages the wrong person or hides inside noise. It has its own owner and its own runbook, so it deserves its own signal. The setup is in the Together AI status alerts guide.

Frequently Asked Questions

What does a 401 from the Together AI API actually mean?

It means the credential attached to the request was not accepted, and nothing about the body, the model or your usage was even examined. That is the useful part: a 401 is decided before any of your parameters matter, so re-reading your payload for a mistake is wasted effort. It also means the service is healthy — Together AI answered you, promptly and deliberately, which is the opposite of an outage. A 401 should never be counted against Together AI availability in your own metrics, and a monitor that treats every non-2xx as downtime will page you for your own expired secret.

My Together AI key works for one model and fails for another. Is the key bad?

Almost certainly not. Together is a marketplace, so authentication and authorisation are answered separately: the account is identified once, and then each model id is independently gated by licence acceptance, availability and deployment type. A credential that is valid everywhere can still be refused for a specific model, and that refusal is an authorisation decision rather than an identity one. Read the status code rather than the general shape of the error — if the same key succeeds against your primary model in the same minute, rotating it cannot possibly help and will only cost you a deploy.

Why did my fallback chain start returning auth errors during an incident?

Because the fallback branch had never been exercised. The primary model was granted and working, the alternate was configured months ago and never actually called, and the first request it ever received arrived during an incident — when the account had never been granted access to that model id. Resilience machinery that is only ever executed under failure is untested code in the worst possible place. Run a low-volume synthetic call through every branch of the chain on a schedule so an ungranted model surfaces on a Tuesday morning instead of mid-incident.

Should I retry a 401?

Not with the same credential, and this is where a lot of retry code does real damage. A 401 is deterministic: the identical request with the identical key will be refused every time, so a backoff loop turns one refusal into dozens without any possibility of success, and on some providers a burst of failed auth attempts attracts additional protective rate limiting on top. The correct handling is to fail fast, surface the error to an operator rather than an end user, and only retry after the credential has actually changed — a rotation, a re-fetch from the secret store, a refreshed cache. If your client treats 4xx and 5xx with the same policy, this is the error that proves the two need splitting.

How do I tell a Together AI 401 from a 403?

By asking which question the service refused to answer. A 401 says it does not know who you are: the credential was missing, malformed, expired or revoked. A 403 says it knows exactly who you are and this identity is not permitted to do this thing — most often on Together, a model id this account has not been granted. The distinction determines who fixes it. A 401 is fixed by an engineer with access to the secret store, usually in minutes. A 403 is fixed by whoever administers the account, and no amount of rotating keys will move it. On a marketplace this split matters more than anywhere else, because the 403 branch is the common one.

How do I stop 401s from recurring after every key rotation?

By making rotation overlapping rather than atomic. The failure is structural: a rotation that invalidates the old key at the instant the new one is issued guarantees a window in which some running processes still hold the dead credential, and the length of that window is your deploy time, not your intent. Issue the new key, roll it everywhere, verify with a synthetic call from every environment, and only then revoke the old one. Have clients read the secret from a store at request time or on a short refresh rather than caching it at process start, so a rotation does not require a restart to take effect. The full sequence is in the Together AI key rotation guide.

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