From Anthropic

Radium serves the Anthropic Messages endpoint at POST /v1/messages. The Anthropic SDK, Claude Code, PydanticAI, and any framework that targets Anthropic can point at Radium by changing the base URL.

Before and after

Python

  from anthropic import Anthropic
  client = Anthropic(
-     api_key=os.environ["ANTHROPIC_API_KEY"],
-     base_url="https://api.anthropic.com",
+     api_key=os.environ["RADIUM_API_KEY"],
+     base_url="https://api.radium.cloud",
  )
  response = client.messages.create(
-     model="claude-4-sonnet-20250929",
+     model="clarke-1.0",
      max_tokens=1024,
      messages=[{"role": "user", "content": "Hello"}],
  )

TypeScript

  import Anthropic from "@anthropic-ai/sdk";
  const client = new Anthropic({
-   apiKey: process.env.ANTHROPIC_API_KEY,
-   baseURL: "https://api.anthropic.com",
+   apiKey: process.env.RADIUM_API_KEY,
+   baseURL: "https://api.radium.cloud",
  });
  const response = await client.messages.create({
-   model: "claude-4-sonnet-20250929",
+   model: "clarke-1.0",
    max_tokens: 1024,
    messages: [{ role: "user", content: "Hello" }],
  });

Supported endpoints

Endpoint	Status
`POST /v1/messages`	Supported
`POST /v1/messages/count_tokens`	Supported

Reading the response

When reasoning is enabled, the response contains a thinking content block before the text block. Read the last content block, not the first one. This is the same pattern the Anthropic SDK uses.

# Correct: read the last block
print(response.content[-1].text)

# Incorrect: may return the thinking block
print(response.content[0].text)

Prompt caching

The cache_control parameter is supported on all models. Cache hits reduce latency by approximately 50% and billed at the cached input rate.

Known differences

Model strings are different. Using claude-* returns a model-not-found error.
Radium does not publish the names of underlying open-weight models.
Rate limits and pricing differ. See Rate limits and Pricing.

Model mapping

Anthropic model	Radium equivalent
Claude 4 Opus	Hal 1.0
Claude 4 Sonnet	Clarke 1.0
Claude 4 Haiku	Tycho 1.0

Getting started

Models

Switching

Core concepts

Tools

Guides

Enterprise

From Anthropic

From Anthropic

Before and after

Supported endpoints

Reading the response

Prompt caching

Known differences

Model mapping

​From Anthropic

​Before and after

​Supported endpoints

​Reading the response

​Prompt caching

​Known differences

​Model mapping

From Anthropic

Before and after

Supported endpoints

Reading the response

Prompt caching

Known differences

Model mapping