Migrate from Anthropic

FluxRouter speaks the Anthropic Messages API. If your code already calls Anthropic, you keep the same SDK and the same request shape. You change three things:

1. Base URL to https://api.fluxrouter.ai/anthropic
2. API key to your Flux key (sk-... from the dashboard)
3. Model to flux-auto (or a specific flux-* id)

The endpoint (/anthropic/v1/messages), the request and response JSON, streaming, and tool use all stay the same.

How auth works on the Anthropic endpoint#

The Flux Anthropic endpoint accepts your key two ways:

• As x-api-key: sk-... (the Anthropic SDK default), or
• As Authorization: Bearer sk-....

The Anthropic SDK sends x-api-key automatically when you set its API key, so you don't have to do anything special.

Get a Flux key#

Sign up at /auth/sign-up, open the dashboard, and create an API key. It looks like sk-.... The examples below read it from a FLUX_API_KEY environment variable.

Migrate the Python SDK#

Before (Anthropic)#

from anthropic import Anthropic

client = Anthropic(
    api_key="sk-ant-...",
)

message = client.messages.create(
    model="claude-sonnet-4-5",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Say hello."}],
)

print(message.content[0].text)

After (FluxRouter)#

from anthropic import Anthropic

client = Anthropic(
    api_key="sk-...",                                # your Flux key (sent as x-api-key)
    base_url="https://api.fluxrouter.ai/anthropic",  # the one line you change
)

message = client.messages.create(
    model="flux-auto",                               # let Flux route, or pin a flux-* id
    max_tokens=1024,
    messages=[{"role": "user", "content": "Say hello."}],
)

print(message.content[0].text)

Migrate the Node SDK#

Before (Anthropic)#

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY,
});

const message = await client.messages.create({
  model: "claude-sonnet-4-5",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Say hello." }],
});

console.log(message.content[0].text);

After (FluxRouter)#

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic({
  apiKey: process.env.FLUX_API_KEY,                  // your Flux key (sent as x-api-key)
  baseURL: "https://api.fluxrouter.ai/anthropic",    // the one line you change
});

const message = await client.messages.create({
  model: "flux-auto",                                // let Flux route, or pin a flux-* id
  max_tokens: 1024,
  messages: [{ role: "user", content: "Say hello." }],
});

console.log(message.content[0].text);

What stays the same#

Everything except the three values above:

• The Anthropic SDK and its method names (messages.create).
• The endpoint: /anthropic/v1/messages.
• The request and response JSON, including max_tokens, system prompts, streaming, and tool use.
• Your prompts, message arrays, and parameters.

What to do about the model field#

Anthropic model ids like claude-sonnet-4-5 are not Flux models. Pick one of these instead:

• flux-auto (recommended): Flux routes each request to a sensible model for the prompt.
• A tier alias (flux-fast, flux-standard, flux-reasoning, flux-image) or a flux-pinned-* id when you want the same backing model every time.

The authoritative list of model ids is GET https://api.fluxrouter.ai/v1/models. See Models.

Next steps#

• Models: every model alias and how flux-auto and pinning work.
• Connect your tools: wire up Claude Code or another Anthropic-protocol tool.