Error 400: what to do when claude-opus-4-8 fails

A 400 means the request itself is invalid — a missing field, a wrong type, or a parameter this model does not support. Retrying will not help; the request body must change.

400 Bad Request means the server refuses to process the request because the body itself is invalid. Unlike 5xx, a 400 will not resolve by retrying — you get the same response every time. The parameters must be fixed first.

claude-opus-4-8 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: A required field is missing (model or messages). The recommended first action is: Check the request body against the parameter table on this page.

Common causes

  • A required field is missing (model or messages)
  • A parameter has the wrong type
  • A parameter is not supported by this model
  • messages is malformed or role has an invalid value

How to fix

  • Check the request body against the parameter table on this page
  • Remove unsupported parameters and retry
  • Make sure messages is an array with valid role values
  • Start from a minimal request, then add parameters one by one

Retry with exponential backoff

The snippet below retries when claude-opus-4-8 returns 400, 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-opus-4-8'


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 * 5 + cr * 0.5 + cc * 6.25 + cc1h * 10 + c * 25

FAQ

Will I be charged when claude-opus-4-8 returns 400?

No charge — only output actually produced counts toward usage. Only the output already produced is billed; the failed part is not. Input price is about $5.00 per million tokens. With billing p * 5 + cr * 0.5 + cc * 6.25 + cc1h * 10 + c * 25, the cost of long output comes mostly from output tokens. Check your balance and rate limits in the console before debugging code. When estimating cost from p * 5 + cr * 0.5 + cc * 6.25 + cc1h * 10 + c * 25, include the retry budget.

Is 400 more likely in multi-turn conversations with claude-opus-4-8?

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 400.

400 keeps recurring on claude-opus-4-8 — how do I tell whether it is the model or my account?

This error is unrelated to model capability; it is a gateway-layer issue. It is usually transient and recovers on its own. 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.

Can switching to a comparable model from another vendor fix 400?

Keep a fallback model ready as well. Building a fallback into the architecture is more reliable than patching errors one by one. This model from Anthropic has several upstream nodes the gateway can switch between. Keep a lighter fallback model ready so the main flow never breaks. Put the model name in config, so switching upstreams needs no code change.

Other errors on this model

Other models with the same error

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Data updated: 2026-10-11 19:15

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