Error 400: what to do when claude-sonnet-4-5 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-sonnet-4-5 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-sonnet-4-5 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-sonnet-4-5'


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

When claude-sonnet-4-5 returns 400, which fields should I read in the response body?

Group the errors by time and node first; the pattern is usually obvious once you do. This model is served by Anthropic, so upstream status follows the vendor’s own announcements. Log the request ID on every failure — it beats the status code when debugging.

Do failed requests count against my rate limit quota?

No charge — only output actually produced counts toward usage. Only the output already produced is billed; the failed part is not. With billing p * 3 + cr * 0.3 + cc * 3.75 + cc1h * 6 + c * 15, failed requests are not counted toward usage. When estimating cost from p * 3 + cr * 0.3 + cc * 3.75 + cc1h * 6 + c * 15, include the retry budget.

Can setting max_tokens too high trigger 400?

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. The 1M context window sets the maximum input per request; anything beyond it is rejected outright. Fail fast on parameter errors instead of spending retries on them. Truncate or summarise long inputs — it noticeably reduces 400.

Will retrying cause the request to run twice?

You usually do not need to change business code, just the call cadence. Retrying is the most effective first step. With billing p * 3 + cr * 0.3 + cc * 3.75 + cc1h * 6 + c * 15, failed requests are not counted toward usage. Set the retry ceiling to 3–5 attempts and add jitter. Use exponential backoff for retryable errors and return immediately for the rest.

Other errors on this model

Other models with the same error

Back to the model page

Data updated: 2026-10-12 02:10

Technical SupportLive Support
Back to Top