AI coding agents on Windows

By Julien Abenhaim, founder of Castforge. Published 7 September 2026.

All the main ones run on Windows today, as command-line tools you install yourself. What differs between them is how you sign in, and how much Windows-specific friction sits in the way: your PATH, a SmartScreen caution screen on a new installer, and a couple of look-alike traps that cost an afternoon each if you do not know about them.

What runs on Windows today

The lineup is bigger than most people expect, and it keeps growing. The ones you are most likely to reach for:

GitHub Copilot, the free starting point, and the one to try first if you have never run an agent from a terminal.
Claude, Anthropic's Claude Code.
OpenAI Codex, which you sign in to with ChatGPT.
Google Gemini.
Cursor, through its separate cursor-agent command-line tool.
Factory Droid.
OpenRouter, which gives you bring-your-own-key access to many models through one provider.
A local model, running on your own machine through Ollama.

Claude, Codex and Gemini install through npm and want Node.js 20 or newer, so install Node first if you do not have it. The local model uses the Ollama installer instead.

Three ways to sign in

Whichever agent you pick, there are three ways in, and you only need one of them.

Free. A GitHub Copilot sign-in, no credit card. This is the lowest-friction start, and it is enough to see whether any of this suits how you work.

A subscription you already pay for. If you already have Claude, ChatGPT, Gemini or Cursor, sign in with that instead. You are using an entitlement you are already buying rather than opening a second meter.

Your own API key. From Anthropic, OpenAI, Google, OpenRouter or another provider. A key belongs in your operating system's credential store, not in a .env file you commit. That is worth saying plainly, because a key pasted into a repository is the single most common way one leaks.

What actually trips people up

Four things, and none of them are hard once you know what you are looking at.

The tool is installed but not on your PATH. The install succeeded, and the app still cannot find it, because the shell that launched the app never picked up the new path. Restarting the app after an install usually fixes it.
SmartScreen warns on a new installer. This is expected rather than a sign of trouble: SmartScreen earns trust per certificate over the first weeks of installs, so a new certificate always starts cold. Choose "More info" and then "Run anyway" if you recognize the publisher.
The Cursor editor is not the Cursor CLI. Having the editor installed, or even open, is not the same as having cursor-agent, and only the command-line tool can be driven by anything else.
A brand-new GitHub account has no Copilot plan. Your sign-in worked; what failed is permission. Switch on Copilot Free once at github.com/settings/copilot. Signing in again will not help. On a work or school account, the same message can mean an administrator has disabled the Copilot command-line tool by policy.

What this does not solve

Castforge is Windows only today, Windows 10 or Windows 11. There is no macOS or Linux build yet.
Every agent still needs its own command-line tool installed and its own sign-in. Nothing here replaces that.
A new GitHub account has no Copilot plan until you switch on Copilot Free once. It is free and takes a few seconds, but it is a step.
SmartScreen will most likely warn on the first run of a new installer. The publisher line reads 9569-2893 Québec Inc., which is the registered company behind Castforge.
Local models run at the speed of your own machine. A large model on modest hardware is slower than a hosted one, and that is a hardware fact, not a setting.

Driving them from one window

Castforge is a Windows desktop workspace for the agents above. It connects the ones you already have access to, free, by subscription or with your own key, and puts each on the seat it suits, so your strongest model does the work that needs it. Your keys stay in your machine's keychain and are never sent to Castforge's servers.

It is in open beta and free during early access. You can download it, or read the full connection guide in connecting AI agents.

Run Claude Code and Codex on the same project. What actually goes wrong when two agents share one repository, and the splits that hold.
What is a reviewed AI dev team?. Roles, review gates, and what a gate is actually worth when it passes.
All Castforge walkthroughs.