Coding Agents & IDEs
Point your editor or CLI at Radium. Claude Code, Cursor, VS Code, and the rest, each in four steps or fewer.

Use Radium with Cursor
Connect Radium's Tycho model to Cursor using Cursor's built-in OpenAI-compatible API support. Settings, model ID, verification, and troubleshooting.
Use Radium with Cursor
Cursor has built-in support for OpenAI-compatible APIs, and Radium serves one, so connecting Tycho is four settings and no plugin.
This page covers Tycho specifically. Any Radium model reachable through the OpenAI-compatible endpoint can be added the same way by repeating step three with a different model identifier.
Scope
This connects Radium to Cursor Chat and Cursor Agent. Cursor Tab, the inline autocomplete, keeps using Cursor's own model regardless of what you select here. See About Tab autocomplete.
Before you start
Cursor installed
A Radium API key
Open model settings
In Cursor, go to:
Cursor Settings → Models
Connect the API
Radium's API is OpenAI-compatible, so the connection goes under the OpenAI section of the Models panel, not Anthropic. Under API Keys, set:
Setting
Value
OpenAI API Key
Your Radium API key
Override OpenAI Base URL
https://api.radium.cloud/v1
Enable both toggles, OpenAI API Key and Override OpenAI Base URL. Neither takes effect while off.
The one to get right
This goes in the OpenAI fields even though you are not using OpenAI. Cursor does not have a generic custom-provider slot, and the OpenAI-compatible one is the correct place for any OpenAI-shaped endpoint, Radium included.
Add Tycho
Still in the Models panel, select Add Custom Model and enter the identifier exactly:
tycho-1.0
Enable the model once it is added. It will not appear in the picker otherwise.
Verify the connection
Open a new Cursor Chat or Agent session and select 
tycho-1.0 from the model picker. Send:
Reply with exactly: RADIUM_OK
Expected response:
RADIUM_OK
If you see that, the connection is live and Tycho is answering Chat and Agent requests.
About Tab autocomplete
Cursor Tab, the inline completion as you type, continues to run on Cursor's own model no matter what is selected in the Models panel. Radium serves 
tycho-1.0 for Chat and Agent sessions only. This is a Cursor limitation, not a Radium one, and there is currently no setting that changes it.
When it does not work
Confirm the base URL includes 
/v1. Without it, requests go to the wrong path.
Confirm the model ID is exactly 
tycho-1.0. Cursor does not correct typos in a custom model entry.
Confirm the OpenAI API Key toggle is enabled, not just filled in.
Start a new Cursor session after selecting Tycho. An existing session can keep using whatever model it started with.
Fully quit and restart Cursor if the new settings do not take effect. Cursor does not always pick up a provider change without a restart.
Next
API quickstart, for calling Radium directly
Use Radium with Claude Code
Tool calling

Run Claude Code on Radium
Point the Claude Code CLI at Radium's Anthropic-compatible Messages API. Setup script, manual configuration, model selection, and troubleshooting.
Run Claude Code on Radium
Claude Code sends Anthropic-compatible API traffic to whatever endpoint you point it at, and Radium serves an Anthropic-compatible Messages API, so moving Claude Code across is a change of base URL, model name, and key.
Your projects stay where they are. So do your prompts, your permissions, your local tools, and any MCP servers you have configured. Claude Code keeps running the session and Radium answers the model calls.
Supported models
hal-1.0, 
clarke-1.0, and 
tycho-1.0. The examples on this page use 
hal-1.0, and any of the three can be substituted wherever it appears.
What changes
What you change
The API base URL
The model name
Your credentials
One settings file
What stays put
Your prompts and project context
Local tools and permissions
MCP servers and their configuration
Everything about how you work
Settings used throughout this guide
Setting
Value
API base URL
https://api.radium.cloud
Model
hal-1.0, 
clarke-1.0, or 
tycho-1.0
Authentication
Radium API key
Settings file
~/.claude/settings.json
Read this one twice
Claude Code appends 
/v1/messages to the base URL on its own, so leave it off. Setting 
ANTHROPIC_BASE_URL to the full Messages endpoint is the most common way this goes wrong, and it returns a 404 every time.
Before you start
A Radium API key
Claude Code, installed and current
Node.js 18 or later, if you plan to run the setup script or the verifier
macOS, Linux, or a supported Windows environment such as WSL or Git Bash
Check what you have:
node --version
claude --version
If Claude Code is not installed:
npm install -g @anthropic-ai/claude-code
Setup with the script
Run this from the folder containing the integration package:
./01-setup-radium-api.sh \
  --api-base api.radium.cloud \
  --model hal-1.0
The script asks for your API key without printing it, and then it does five things:
Normalises the base URL, so a trailing slash or a missing scheme does not break anything.
Backs up your existing 
~/.claude/settings.json with a timestamp.
Preserves every setting already in the file that has nothing to do with Radium.
Writes the base URL, the model, and the key.
Restricts the file permissions to your user.
The backup lands beside the settings file, named like this:
~/.claude/settings.json.bak.20260807153000
Nothing you had configured is lost, and you can put it back by hand in one move.
Setup by hand
If you would rather not run a script against your machine, add these entries to 
~/.claude/settings.json yourself:
{
  "env": {
    "ANTHROPIC_BASE_URL": "https://api.radium.cloud",
    "ANTHROPIC_MODEL": "hal-1.0",
    "ANTHROPIC_API_KEY": "YOUR_RADIUM_API_KEY"
  }
}
Keep any other settings that are already in the file, and keep the JSON valid. Then restrict access to it:
chmod 600 ~/.claude/settings.json
Shell environment variables work too, and they override the settings file, which is worth remembering when something behaves strangely later:
export ANTHROPIC_BASE_URL="https://api.radium.cloud"
export ANTHROPIC_MODEL="hal-1.0"
export ANTHROPIC_API_KEY="$RADIUM_API_KEY"
Verify the connection
Test Radium directly first, then test Claude Code. Doing it in that order tells you which of the two is at fault when something fails.
Step one, the endpoint on its own:
./02-test-radium-api.mjs --model hal-1.0
Step two, through Claude Code:
claude -p "Say only: radium model connected."
You should get back:
radium model connected.
Then open a project and work normally:
cd YOUR_PROJECT
claude
If step one passes and step two fails, the problem is in Claude Code's configuration and not in the endpoint.
Choosing a model
Primary model selection
Model
Built for
hal-1.0
Higher-capability coding and agentic work
clarke-1.0
General-purpose and structured work
tycho-1.0
Faster, lighter-weight tasks
To change it, run the setup script again with a different model:
./01-setup-radium-api.sh \
  --api-base api.radium.cloud \
  --model clarke-1.0
Another backup is written before anything is overwritten.
A faster model underneath
Claude Code reaches for a smaller model to handle helper operations during a session, and those operations are the kind of work Tycho is built for. Running Hal as the primary with Tycho underneath puts each task on the model sized for it, and the session gets quicker in the places where capability was never the constraint.
{
  "env": {
    "ANTHROPIC_BASE_URL": "https://api.radium.cloud",
    "ANTHROPIC_MODEL": "hal-1.0",
    "ANTHROPIC_SMALL_FAST_MODEL": "tycho-1.0",
    "ANTHROPIC_API_KEY": "YOUR_RADIUM_API_KEY"
  }
}
Some Claude Code versions and some Radium deployments need this set explicitly, and others do not. Confirm the mapping with Radium before you rely on it in a managed deployment.
Bearer-token deployments
Radium deployments authenticate one of two ways. The default is an API key, and some deployments use a bearer token instead. Use whichever mode Radium supplied, and start with the API key when nobody has told you otherwise.
With the script:
./01-setup-radium-api.sh \
  --api-base api.radium.cloud \
  --model hal-1.0 \
  --auth bearer
By hand, swap the key variable for the token variable:
{
  "env": {
    "ANTHROPIC_BASE_URL": "https://api.radium.cloud",
    "ANTHROPIC_MODEL": "hal-1.0",
    "ANTHROPIC_AUTH_TOKEN": "YOUR_RADIUM_API_KEY"
  }
}
Set one or the other. Setting both is a 401 waiting to happen.
When it does not work
404 on every request
The base URL has a path on it. Use 
https://api.radium.cloud and let Claude Code add 
/v1/messages itself.
401 or 403
Check that the key belongs to the environment you are pointing at, check whether the deployment expects an API key or a bearer token, and check that only one of 
ANTHROPIC_API_KEY and 
ANTHROPIC_AUTH_TOKEN is set. Restart Claude Code after any change.
Claude Code still appears to reach Anthropic
Look at 
~/.claude/settings.json and confirm the base URL, then look for shell environment variables overriding it, because they win. Close any open sessions and start a new one. If you are still unsure, run the direct verifier, which separates an endpoint problem from a configuration problem.
Model not found
Use the exact identifier issued for your account. This integration supports 
hal-1.0, 
clarke-1.0, and 
tycho-1.0.
Tools or streaming behave differently
Claude Code uses streaming, tool calls, and more than one model route in a single session. API compatibility covers the shape of the request and it does not guarantee that every model responds the same way, so run the workflows your team actually uses before a broad rollout.
Security and operations
Never commit 
~/.claude/settings.json or any populated credential file.
The setup script stores your key locally in that settings file, so organisations that require short-lived credentials should use a managed key helper or a gateway instead.
Prompts, tool results, and attached project context are data sent to the configured endpoint, and they should be treated that way.
Use separate keys for development, staging, and production.
Test quality, tool behaviour, latency, and usage on repositories that look like your real ones.
Point it at a real project, run a day of work through it, and you will know.
Next
API quickstart, for calling Radium directly
Tool calling, for the Messages API tool contract
MCP and Radium, for how MCP servers fit alongside Claude Code
Errors and troubleshooting