Anthropic (Claude) API key

To get an Anthropic Claude API key, sign in to the Claude Console at platform.claude.com, open Settings → API keys, and click Create Key. An Anthropic API key starts with sk-ant- and is shown only once at creation. Anthropic's console moved from console.anthropic.com to platform.claude.com, and the keys page now lives at platform.claude.com/settings/keys. An Anthropic API key authenticates requests to https://api.anthropic.com with the x-api-key header and an anthropic-version header — not with Authorization: Bearer. Anthropic's pricing FAQ states that new users receive a small amount of free credits to test the API; there is no free tier beyond that grant, so Claude API usage is billed per token once the initial credits are spent.

Kunavo is an independent, OpenAI-compatible AI API gateway: one API key and one pay-as-you-go balance reach Claude, Gemini, GPT and image, video and audio models, with no per-provider account required. A Kunavo API key starts with sk-kn-, is created at kunavo.com/app/keys, and requires no Anthropic account. Kunavo serves Claude through both the OpenAI-compatible endpoint https://api.kunavo.com/v1/chat/completions and the native Anthropic endpoint https://api.kunavo.com/v1/messages, so the official OpenAI SDK reaches Claude by changing only base_url. Kunavo is pay-as-you-go from a $10 minimum top-up and gives new accounts no free credit.

Option A — an API key direct from Anthropic

An Anthropic Console key is the right choice when Claude is the only model the project will ever call. Anthropic bills the key per token and supports every Claude feature on the day it ships.

1. Go to platform.claude.com and sign in. The older address console.anthropic.com now points at the same console.
2. Open Settings → API keys (direct link: platform.claude.com/settings/keys) and click Create Key. Anthropic keys look like sk-ant-... and are shown once.
3. Add a payment method under Billing. Anthropic grants new users a small amount of free credits, then bills per token.
4. Send the key as x-api-key, alongside an anthropic-version header.

# Anthropic direct — x-api-key, not Bearer
curl https://api.anthropic.com/v1/messages \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 256,
    "messages": [{"role": "user", "content": "Hello, Claude"}]
  }'

One consequence worth planning for: an Anthropic key reaches Claude only. A project that also calls Gemini, GPT, image or video models needs a separate account, key, SDK and invoice per provider.

Option B — one Kunavo key for Claude and everything else

Kunavo fronts Claude behind both an OpenAI-compatible API and the native Anthropic Messages API. One sk-kn- key reaches Claude and every other model in the catalog, on a single Stripe-funded balance, without an Anthropic account.

1. Create a Kunavo account and add a $10 top-up. Kunavo is pay-as-you-go and the balance never expires.
2. Generate a key at /app/keys. A Kunavo key is shown once; store the key in an environment variable.
3. Point the OpenAI SDK at https://api.kunavo.com/v1 and call a Claude slug.

Claude API key vs Anthropic API key

An “Anthropic API key” and a “Claude API key” are the same credential under two names. Anthropic is the company, Claude is the model family, and the key created in the Claude Console authenticates Claude API calls. What differs between the two keys below is where each key comes from and what each key can reach:

• Anthropic Console key (sk-ant-...) — created at platform.claude.com/settings/keys. An Anthropic Console key calls Claude only, and Anthropic bills the key per token.
• Kunavo key (sk-kn-...) — created at kunavo.com/app/keys. A Kunavo key calls the same Claude models through the OpenAI SDK or the native Messages API, plus Gemini, GPT, image, video and audio models, on one Stripe-funded balance and without an Anthropic account.

Call Claude with Python

Keep the official OpenAI SDK. Changing base_url and the model name is the whole migration.

import os
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["KUNAVO_API_KEY"],
    base_url="https://api.kunavo.com/v1",  # the only line that changes
)

resp = client.chat.completions.create(
    model="claude-sonnet-4-6",
    messages=[{"role": "user", "content": "Explain quicksort in one paragraph."}],
)
print(resp.choices[0].message.content)

Call Claude with Node.js

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.KUNAVO_API_KEY,
  baseURL: "https://api.kunavo.com/v1",
});

const resp = await client.chat.completions.create({
  model: "claude-sonnet-4-6",
  messages: [{ role: "user", content: "Explain quicksort in one paragraph." }],
});
console.log(resp.choices[0].message.content);

Or call Claude with curl

curl https://api.kunavo.com/v1/chat/completions \
  -H "Authorization: Bearer $KUNAVO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "messages": [{"role": "user", "content": "Hello, Claude"}]
  }'

Claude API key not working

A Claude API key that returns 401 authentication_error is almost always one of five things: the wrong header for the endpoint, a key sent to an endpoint that key does not belong to, whitespace or quotes smuggled into the environment variable, a revoked key, or the wrong base URL for that key.

The single most common cause is a header mismatch. Anthropic's native API expects x-api-key plus anthropic-version. OpenAI-compatible endpoints, Kunavo included, expect Authorization: Bearer. An sk-ant- key works only against api.anthropic.com, and an sk-kn- key works only against api.kunavo.com.

Each error below has a dedicated deep-dive with the exact error JSON, every known cause and copy-paste fixes: 401 invalid api key, 429 rate_limit_error, credit balance too low / 402, 529 overloaded and model_not_found.

Using the Claude API without a credit card

Anthropic accepts major credit cards for standard Claude API accounts and reserves invoicing for enterprise customers, so on the direct route a card is the practical requirement.

A Kunavo balance can be funded without a card at all, on any of these rails: ACH bank transfer (United States), Alipay (mainland China), WeChat Pay (mainland China), Pix (Brazil), Bancontact (Belgium), BLIK (Poland), EPS (Austria), MB WAY (Portugal). Kunavo prices top-ups in USD and Stripe converts on the checkout page, so a Brazilian buyer scans a Pix code for an amount in reais rather than hunting for a card cleared for international purchases. Card-backed wallets are available too and are left out of that list on purpose, because a wallet riding on a card does not answer the question. The full method list is in the billing reference.

Which Claude model to use

• claude-haiku-4-5 — cheapest and fastest, for high-volume classification and support. Kunavo prices Claude Haiku 4.5 at $0.40 per 1M input tokens and $2.00 per 1M output tokens.
• claude-sonnet-4-6 — the balanced default for most reasoning, retrieval and coding. Kunavo prices Claude Sonnet 4.6 at $1.20 / $6.00 per 1M tokens, against Anthropic's list price of $3.00 / $15.00.
• claude-sonnet-5 — the newest Sonnet: near-Opus coding and agentic quality at Sonnet cost.
• claude-opus-5 — heavy reasoning and long context. Kunavo prices Claude Opus 5 at $2.00 / $10.00 per 1M tokens, against Anthropic's list price of $5.00 / $25.00.
• claude-fable-5-1 — Anthropic's most capable model, for frontier reasoning and long-horizon agents, released September 1, 2026. Kunavo prices it at $7.00 / $35.00 per 1M tokens, against Anthropic's list price of $10.00 / $50.00. The previous release, claude-fable-5, is still served at the same rate.

API key security checklist

• Never expose an API key client-side. Proxy every call through a server the developer controls.
• Use one API key per project or environment so a leaked key can be revoked without taking down everything else.
• Rotate API keys quarterly. Kunavo allows multiple live keys at once, which gives a rotation a clean overlap window.

FAQ

What Kunavo is, and is not

Kunavo is an independent, OpenAI-compatible AI API gateway: one API key and one pay-as-you-go balance reach Claude, Gemini, GPT and image, video and audio models, with no per-provider account required.

Kunavo is an independent gateway that resells access to these models. Kunavo is not Anthropic, Google or OpenAI, and Kunavo does not train or host the models it serves.

Anthropic's own documentation at platform.claude.com is the authoritative source for Anthropic's product, pricing and policy. This page reproduces Anthropic's published procedure with the date each claim was verified, and states Kunavo's alternative beside it.

Where to go next

• Messages API reference (native Anthropic shape)
• Claude API pricing 2026
• Quickstart — your first request in 60 seconds