Error 401: what to do when claude-sonnet-4-5-20250929 fails

A 401 means authentication failed: the request carries no API key, or the key is invalid, deleted or expired.

401 Unauthorized means the request carries no valid credential. The gateway could not identify the caller, so the request never reaches the upstream model. Checking the Authorization header and the key status is the only path forward.

claude-sonnet-4-5-20250929 is served by Anthropic. Everything on this page — triggers, fixes and measured data — is compiled from the real runtime behaviour of this model at the gateway layer.

At this gateway, the most common trigger is: The Authorization header is missing. The recommended first action is: Send the header as Authorization: Bearer followed by your key.

Common causes

  • The Authorization header is missing
  • The key is misspelled or has stray whitespace
  • The key was deleted or disabled on the Tokens page
  • A key from another platform was used by mistake

How to fix

  • Send the header as Authorization: Bearer followed by your key
  • Generate a fresh key on the Tokens page
  • Check that you are not using a key from another service
  • Verify the key with a minimal curl request

Retry with exponential backoff

The snippet below retries when claude-sonnet-4-5-20250929 returns 401, up to 5 attempts, with an increasing wait plus random jitter so concurrent calls do not retry in lockstep. Read the base URL and API key from environment variables — never hardcode them.

import os, time, random
import requests

BASE  = os.getenv("OPENAI_BASE_URL")   # e.g. https://<your-gateway>/v1
KEY   = os.getenv("OPENAI_API_KEY")
MODEL = 'claude-sonnet-4-5-20250929'


def chat(messages, retries=5):
    """Retry with exponential backoff + jitter."""
    for i in range(retries):
        try:
            r = requests.post(
                BASE + "/chat/completions",
                headers={"Authorization": "Bearer " + KEY},
                json={"model": MODEL, "messages": messages, "stream": True},
                timeout=60,
            )
            if r.status_code == 429 or r.status_code >= 500:
                time.sleep(min(2 ** i + random.uniform(0, 1), 30))
                continue
            r.raise_for_status()
            return r.json()
        except requests.exceptions.Timeout:
            time.sleep(min(2 ** i + random.uniform(0, 1), 30))
    raise RuntimeError("gave up after " + str(retries) + " retries")


print(chat([{"role": "user", "content": "hello"}]))

Key facts for this model

API endpointhttps://api.airai.cc/v1
OpenAI-compatibleOpenAI-compatible
VendorAnthropic
Context1M
CapabilitiesReasoning, Tools, Files, Vision
API formatsopenai, openai-response, openai-response-compact, anthropic, gemini, openai-alpha-search
Billing formulap * 3 + cr * 0.3 + cc * 3.75 + cc1h * 6 + c * 15

FAQ

Is 401 related to the capability of the model itself?

This error is unrelated to model capability; it is a gateway-layer issue. The capability tags for this model are Reasoning, Tools, Files, Vision. If it persists for several minutes, contact platform support to confirm upstream status. Decide account-level versus model-level first; the two need completely different handling.

Do I need to upgrade my plan to fix 401 on claude-sonnet-4-5-20250929?

It is mainly a quota matter, not a fault in the model itself. Raising the plan ceiling or lowering the call rate both help. With billing p * 3 + cr * 0.3 + cc * 3.75 + cc1h * 6 + c * 15, the cost of long output comes mostly from output tokens. When estimating cost from p * 3 + cr * 0.3 + cc * 3.75 + cc1h * 6 + c * 15, include the retry budget.

Does a long context window make 401 more likely?

This is a client-side configuration issue; nothing changes server-side. The capability tags are Reasoning, Tools, Files, Vision, and parameter ceilings follow from that capability set. Fail fast on parameter errors instead of spending retries on them. Truncate or summarise long inputs — it noticeably reduces 401.

Will I be charged when claude-sonnet-4-5-20250929 returns 401?

No charge — only output actually produced counts toward usage. Only the output already produced is billed; the failed part is not. Billing follows p * 3 + cr * 0.3 + cc * 3.75 + cc1h * 6 + c * 15, so no output means no charge. With billing p * 3 + cr * 0.3 + cc * 3.75 + cc1h * 6 + c * 15, the cost of long output comes mostly from output tokens. Check your balance and rate limits in the console before debugging code.

Other errors on this model

Other models with the same error

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Data updated: 2026-10-10 15:45

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