Google's Antigravity IDE, along with Cursor, AWS Kiro, and Windsurf, relies on Open VSX, a registry most developers have never heard of, to distribute extensions. This shift represents a fundamental restructuring of how AI-native code editors access the tools developers depend on, and it happened largely because Microsoft locked down its own marketplace.

Why Did Microsoft's Marketplace Restrictions Create an Alternative Ecosystem?

When Cursor, Kiro, Windsurf, and Google Antigravity forked the open-source VS Code codebase to build AI-native editors, they inherited the code but lost access to Microsoft's Visual Studio Marketplace. Microsoft's Terms of Service explicitly prohibit "alternative products built on a fork" from accessing the marketplace, a restriction that was intentional, not accidental.

That licensing wall forced every AI IDE builder to find an alternative distribution channel. Open VSX, started by GitPod in 2020 and later donated to the Eclipse Foundation, became that answer. The registry implements its own API and provides the same publisher-to-developer pipeline: a web interface, a command-line tool called ovsx, and a registry that any compliant editor can point to.

The numbers now justify the infrastructure investment. Open VSX serves over 300 million downloads per month, peaks at 200 million daily requests, and hosts more than 12,000 extensions from 8,000 publishers. In June 2026, Google joined the Eclipse Foundation as a Strategic Member specifically to sponsor Open VSX. AWS had already made the same bet in March, providing infrastructure and becoming a paying enterprise customer.

What Extensions Are Missing From Open VSX, and Why Does It Matter?

Extension parity between Open VSX and Microsoft's marketplace is now substantial, with roughly 90% of popular extensions cross-published to both registries. However, critical gaps remain. Microsoft's own extensions stay behind the marketplace wall and will never appear on Open VSX, including Pylance, C# Dev Kit, C/C++, Live Share, and Remote SSH.

For developers migrating from VS Code to Cursor or Antigravity, these absences can be painful. If you rely on Pylance for Python development or the C# Dev Kit, you will need to plan for alternatives. Pyright is a solid substitute for Python language intelligence, and most AI IDEs now bundle their own language intelligence features, but the gap is real.

There is also a security dimension. In January 2026, VS Code forks were recommending extensions by name that did not exist in Open VSX, leaving unclaimed namespaces open to supply chain attacks. The Eclipse Foundation responded with namespace verification measures, but the lesson is clear: audit your extensions when switching registries, and check open-vsx.org before installing something unfamiliar.

How to Verify Your Extensions Are Available on Open VSX

• Check the Registry: Visit open-vsx.org and search for each extension you rely on before migrating to a new AI IDE. This takes only a few minutes and prevents surprises after you switch.
• Use the CLI Tool: If a specific extension is missing, you can use the ovsx command-line tool to mirror it yourself, provided the license permits. This requires some technical familiarity but is faster than waiting for publishers to cross-publish.
• Contact Publishers Directly: If an extension you need is not on Open VSX, reach out to the publisher and request cross-publishing. Many are responsive, especially as the AI IDE ecosystem grows.
• Dual-Publishing Is Now Standard: For extension authors, publishing to both registries is now table stakes if you want your work to reach the full developer audience across both VS Code and AI IDE ecosystems.

How Is Google Antigravity Using Open VSX for Agent Integration?

Google Antigravity, described as an "agentic IDE" built on a VS Code-style editor and powered by models like Gemini 3.5 Flash and Gemini 3.1 Pro, treats the AI agent as a first-class teammate. The IDE includes an Agent Manager dashboard with deep browser connectivity, allowing agents to plan, code, and validate work autonomously.

Antigravity can integrate third-party tools and services through Model Context Protocol (MCP) servers. For example, developers can connect Replicate, a cloud API platform for running AI models, directly to Antigravity without exposing account credentials. This integration happens through Composio Connect, which manages OAuth, API keys, token refresh, and scopes automatically.

The integration process is straightforward. Developers open Antigravity's MCP configuration file, add the Composio endpoint, and then ask the agent to perform Replicate-related tasks like running Stable Diffusion to generate images, listing uploaded files, or retrieving model documentation. The agent prompts for authentication once, and then the connection is secure and persistent.

This architecture demonstrates how AI IDEs are moving beyond traditional extension models. Instead of static plugins, agents can dynamically access thousands of tools across hundreds of apps through a single MCP endpoint, minimizing context bloat and reducing the back-and-forth between the developer and the AI.

What Does This Mean for the Future of VS Code's Marketplace?

Microsoft's decision to lock down the Visual Studio Marketplace inadvertently created the infrastructure it feared. By forcing AI IDE builders to find an alternative, Microsoft consolidated the entire ecosystem around Open VSX, turned the Eclipse Foundation into a critical infrastructure steward, and brought in Google and AWS as backers.

"Open registries, like Open VSX, are critical infrastructure which keep the global developer ecosystem open to everyone," said Amanda Casari, a Google representative.

Amanda Casari, Google

That statement is not marketing hyperbole. It is an accurate description of what happens when 300 million monthly downloads run through a single registry that three of the world's largest tech companies now depend on. VS Code's marketplace share may still be large, but its growth trajectory has stalled. The Rust community's annual survey showed VS Code usage falling from 61.7% to 51.6% over three years, while Zed surged from near-zero to 18.6%.

Open VSX is the connective tissue of that alternative ecosystem. As more developers adopt AI-native IDEs like Antigravity, Cursor, and Kiro, the registry's importance will only grow. For extension authors, developers, and enterprises, the message is clear: the AI IDE era is here, and the audience that cannot reach you through Microsoft's marketplace is growing every quarter.