`invalid x-api-key`

Claude API (Anthropic) · GET /v1/models/{model_id} · HTTP 401 authentication_error

Status: ✅ verified:server:prod · first seen 2026-10-31 · last confirmed 2026-10-31 · 1 confirmation from 1 vantage

GET /v1/models/{model_id} with an invalid x-api-key returns HTTP 401 "invalid x-api-key" even for a model id that does not exist: the key is checked before the model.

What to do

Send header x-api-key = the account setting api_key.

Example

What probe af:anthropic:probe:invalid-key sends (prod) and what it checks in the answer; apifacts-invalid-key is a deliberately wrong key.

Step 1 → HTTP 401:

GET https://api.anthropic.com/v1/models
x-api-key: apifacts-invalid-key

Step 2 → HTTP 401:

GET https://api.anthropic.com/v1/models/claude-agent-facts-no-such-model
x-api-key: apifacts-invalid-key

Response (only what the probe asserts; other fields omitted):

HTTP 401

{
  "error": {
    "message": "invalid x-api-key"
  }
}

In your code

When an SDK receives this response:

SDK	Raises	Check
Python `anthropic`	`anthropic.AuthenticationError`	`e.status_code == 401` · `e.type == "authentication_error"`
Node `@anthropic-ai/sdk`	`Anthropic.AuthenticationError`	`err.status === 401` · `err.type === "authentication_error"`

Read from the SDK source: anthropic 2.3.0: anthropic/_client.py Anthropic._make_status_error; @anthropic-ai/sdk 1.3.0: core/error.js APIError.generate.

Fix 1:

headers["x-api-key"] = YOUR_API_KEY

Dimensions

env: prod · plan: any · region: any · account_state: anonymous

Evidence

Probe af:anthropic:probe:invalid-key (declarative, source)

Observations: none from reporters yet.

Related errors

x-api-key header is required · GET /v1/models/{model_id} · HTTP 401 authentication_error
Errors are a JSON object {type: "error", error: {type, message}, request_id}; the vendor code is error.type (e.g. authentication_error) and the request id also comes in the request-id header. · GET /v1/models · HTTP 401
invalid x-api-key · GET /v1/models · HTTP 401 authentication_error
x-api-key header is required · GET /v1/models · HTTP 401 authentication_error

Machine access

Match signature (what check() matches): invalid x-api-key

curl -s https://apifacts.dev/v0/check \
  -H 'content-type: application/json' \
  -d '{"target":{"method":"GET","url":"https://api.anthropic.com/v1/models/{model_id}"},"error":{"status":401,"body_excerpt":"invalid x-api-key"}}'

YAML: facts/anthropic/invalid-api-key-before-model-lookup.yaml

Data: CC BY 4.0 · apifacts registry · This page is generated; edit the YAML, not the page.