[Bug] API-key pool does not rotate on Anthropic "credit balance is too low" (400/billing_error) #6958

Client or integration

Direct HTTP/API client

Area

Authentication and account pool

Summary

An Anthropic API-key provider (authMode: "key") with a multi-key apiKeyPool does not rotate to the next key when the current key's organization runs out of prepaid credit. Anthropic answers that case with:

HTTP 400
{"type":"error","error":{"type":"invalid_request_error","message":"Your credit balance is too low to access the Anthropic API. Please go to Plans & Billing to upgrade or purchase credits."}}

(billing_error has also been observed for the same condition.)

The response is returned to the client unchanged. Sibling keys in the pool that still have credit are never tried, and the exhausted key is not cooled down, so subsequent requests keep hitting it.

Expected

1. For key-auth providers with apiKeyPool.length >= 2: treat Anthropic's credit-balance refusal (400 invalid_request_error / billing_error with the "credit balance is too low" message, and 402) as a key-scoped failure — cool that key with a long cooldown and retry on the next key, like the existing 401 path.
2. In combo failover: classify the same refusal explicitly as hop with provider scope, ahead of the generic 400 / invalid_request_error handling (similar to how isResponseFormatCapabilityRefusal is ordered for invalid_request_error没有触发failover #4903), so a failover combo reliably moves to the next target.

Reusing the whole-message pattern already in isAccountRefusal keeps this narrow; ordinary invalid_request_errors would still stop.

Code references (2.83.0)

• src/server/messages-native.ts, src/server/chat-native.ts, src/server/responses/adapter-dispatch.ts: key-pool rotation loops exist only for status === 401 and status === 429 (hasKeyPoolFailover).
• src/providers/key-failover.ts: only rotateKeyOn401 / rotateKeyOn429 (and the rotateProviderTransportOn401|429 wrappers).
• src/oauth/anthropic-account-refusal.ts → isAccountRefusal already recognises the exact credit-balance message for OAuth accounts and rotates the OAuth pool, but key pools don't use it.
• src/combos/failover.ts: hops on 401/402/403/404/408/425/429/5xx; there is no message rule for the credit-balance 400. I have not traced the generic 400 path end to end, so please confirm whether a failover combo currently hops or stops on it.

Use case: a self-hosted hub where background jobs (a memory service) are pinned to anthropic-apikey/… to save subscription quota. With several funded keys in the pool, one org running dry should not take the route down.

Related: #6839 (metered combo targets; doesn't cover rotation within an API-key pool or the 400 classification), #6937 (request-local key round-robin; skips cooldowns but adds no billing cooldown trigger), #1572 (closed; terminal 429/400 re-evaluation).

Reproduction

Found by code reading on 2.83.0, not yet reproduced against a live empty-credit key.

1. Configure an anthropic key-auth provider (authMode: "key") with apiKeyPool of 2+ keys, where the active key's org has $0 prepaid credit and another key's org has credit.
2. POST /v1/messages (or /v1/chat/completions) with model: "<provider>/claude-haiku-5-5".
3. Observe: the 400 credit-balance error is returned; no key-401/key-429-style rotation happens; the next request goes to the same key again.

Version

2.83.0

Operating system

Ubuntu 24.04 (hub), macOS 26 (clients)

Provider and model

anthropic (authMode: key) / claude-haiku-5-5, claude-sonnet-5-5, claude-opus-5-5

Logs or error output

HTTP 400
{"type":"error","error":{"type":"invalid_request_error","message":"Your credit balance is too low to access the Anthropic API. Please go to Plans & Billing to upgrade or purchase credits."}}

Screenshots and supporting files

No response

Redacted configuration

{
  "providers": {
    "anthropic-apikey": {
      "adapter": "anthropic",
      "baseUrl": "https://api.anthropic.com",
      "authMode": "key",
      "apiKeyPool": ["<redacted-1>", "<redacted-2>", "<redacted-3>", "<redacted-4>"]
    }
  }
}

Checks

• I searched existing issues and documentation.
• I removed secrets, tokens, account details, request credentials, and personal data.