Eclipse Theia 1.65 Release: News and Noteworthy

We are happy to announce the Eclipse Theia 1.65 release! The release contains in total 78 merged pull requests. In this article, we will highlight some selected improvements and provide an overview of the latest news around Theia.

For those new to Eclipse Theia, it is the next-generation platform for building IDEs and tools for the web or desktop, based on modern state-of-the-art web technologies. With Theia AI, part of the Theia platform, you can also build AI-powered tools and IDEs with ease. For more details about Eclipse Theia, please refer to this article and visit the Theia website.

We are excited to announce 2025 TheiaCon! TheiaCon is the annual virtual conference focused around the Eclipse Theia ecosystem. It brings together a diverse group of Theia developers, adopters, and other contributors. The program will feature a mix of full-length talks, expert panel discussions and short lightning talks featuring project contributor insights, adopter stories, and work being done in the broader ecosystem. TheiaCon is a virtual event on October 29th and 30th 2025. Don’t miss out on this opportunity to connect with the Theia community and learn about the latest developments – register today!

The Theia project also releases a product, the Theia IDE. The Eclipse Theia IDE is a modern, AI-powered, and open IDE for cloud and desktop environments, aimed at end users. The Theia IDE is based on the Theia platform and also includes advanced AI powered features. For more details, see the Theia IDE website.

If you are looking for a simple way to check out the new release, please download and install the Theia IDE, which is based on Theia 1.65.

Eclipse Theia 1.65: Selected features and improvements

In the following, we will highlight some selected improvements in the new release. As usual, we cannot mention all 78 improvements, however we will focus on the most notable changes as well as changes visible to end users. The corresponding pull requests are linked under the respective heading when applicable.

Native Claude Code IDE Integration

Theia 1.65 introduces the first open-source, native Claude Code IDE integration, delivering a truly integrated AI-in-the-IDE experience that goes far beyond terminal wrappers and basic extensions. Watch the following demonstration video for more details:

Key highlights of this integration:

• Context-aware AI: Claude Code has deep awareness of your IDE’s current context, open files, and editor selections
• Native chat experience: Seamless chat sessions without webview limitations
• Integrated code editing: All changes are tracked and presented in Theia’s native diff editor
• Slash command support: Full support for Claude Code’s built-in and custom slash commands
• Inline AI assistance: Select code and get AI help directly from editors and terminal (Ctrl+I)
• Multi-agent collaboration: Combine Claude Code with other AI agents in Theia’s extensible ecosystem

For a complete overview and in-depth demo, see our detailed blog post about this new extension to the Theia AI ecosystem.

Model Context Protocol (MCP) Server Support

Theia AI has supported the Model Context Protocol (MCP) almost since MCP’s inception, allowing you to connect to MCP servers within Theia AI and the Theia IDE. With Theia 1.65, we’re expanding this support by enabling Theia-based applications to also act as MCP servers. This means that AI agents and other tools (typically running outside of Theia) can now connect to Theia applications and access their exposed functions via MCP.

This bidirectional MCP support provides a complete foundation for seamless AI tool integration and cross-application communication. The new implementation features an HTTP streaming server accessible at http://localhost:3001/mcp for MCP clients, providing a standardized entry point for external tools. The architecture includes comprehensive infrastructure for exposing both UI and backend functionality, ensuring that external applications can access the full range of Theia’s capabilities.

To demonstrate the integration’s potential, the release includes three sample tool implementations that showcase different aspects of the MCP server functionality. The system is built with extensibility in mind, making it straightforward for developers to add new MCP tools and resources as needed for their specific use cases.

This feature enables other AI tools and IDEs (such as VS Code with appropriate extensions) to interact with Theia’s capabilities programmatically, opening up new possibilities for AI-assisted development workflows and tool interoperability. Combined with Theia’s existing MCP client support, this creates a powerful ecosystem where Theia can both consume and provide AI-powered services through the standard MCP protocol.

Backend Preferences Support

Theia 1.65 introduces backend preferences support, enabling server-side components to access configuration values directly. This enhancement is particularly valuable for tools built on Theia that need to work both with and without a frontend interface, such as CLI tools or headless services that share the same codebase as their GUI counterparts.

This capability is especially important for Theia’s common use case where the same tool needs to function across different deployment scenarios – whether as a full IDE with a frontend, as a command-line utility, or as a headless service. Now, backend services can read preferences without requiring any frontend interaction, enabling consistent behavior across all deployment modes.

Note for adopters: This change involves some breaking changes, particularly for imports. Please refer to the migration guide for details on updating your code.

For detailed technical information about the preferences system and how to implement backend preferences in your extensions, see the updated preferences documentation.

Browser-Only Improvements

The browser-only version of Theia received substantial improvements in this release, making it more robust and feature-complete for real development work. “Browser-only” means running Eclipse Theia as a static website without any backend infrastructure, leveraging modern browser capabilities like web workers, web APIs, and web assembly. This deployment variant significantly reduces hosting complexity and costs, making it ideal for certain use cases. For more details, see our blog post on [running Eclipse Theia without a backend] (https://eclipsesource.com/blogs/2024/01/29/running-eclipse-theia-without-a-backend/).

Safari Compatibility: Fixed critical issues preventing browser-only Theia from working in Safari versions before 26 Beta, using navigator.locks to ensure operation atomicity and prevent conflicts.

File Watching: Implemented file system watching capabilities, allowing Theia to detect changes made in other browser tabs (though not from external tools like OPFS Explorer).

Folder Operations: Added support for folder copying, completing the set of basic file operations.

Upload/Download Support:

• Files and folders can now be uploaded with memory-efficient streaming
• Download functionality for individual files and folders (as TAR archives)
• Intelligent filtering excludes common build artifacts (node_modules, dist, .git) by default
• Uses native showSaveFilePicker API when available for better user experience

Search in Workspace: “Search in Workspace” (Cmd/Ctrl + Shift + F) and “Find in Files” (Cmd/Ctrl + P) functionality is now available in the browser-only environment. This implementation respects .gitignore and .ignore/.rgignore files, providing behavior consistent with the desktop version of Theia.

These improvements make the browser-only version of Theia significantly more capable, especially in scenarios where a full backend is not available or desired.

Improve Debugging Capabilities

Debugging capabilities in Theia 1.65 have been enhanced with the addition of “Run to Cursor” and “Run to Line” commands. These features streamline the debugging workflow by allowing developers to quickly continue execution to a specific point in their code.

Features include:

• Run to Cursor: Continue execution to the current cursor position
• Run to Line: Continue execution to the current line
• Multiple access points: Available through command palette, editor context menu, and line number context menu
• Smart positioning: Automatically adjusts target position if the exact location isn’t valid for a breakpoint
• Temporary breakpoints: Uses temporary breakpoints that are automatically cleaned up
• User confirmation: Prompts users when target positions need adjustment

This additions significantly improve Theia’s debugging capabilities and address long-standing feature requests from the community.

Restore Widgets to Main Window from Secondary Windows

Theia 1.65 improves widget management in secondary windows. When a secondary window is closed, widgets are automatically restored to their original location in the main window. The system tracks where widgets were extracted from and restores them appropriately. Widgets without a previous location are placed in the main area by default.

Secondary windows now disable drag-and-drop to maintain simpler widget arrangements, and new widgets opened in secondary windows (such as through toolbar actions) are properly managed during restoration.

The screenshot below demonstrates how to detach and reattach a view:

AI Chat Input History

The AI chat experience has been enhanced with the addition of input history navigation. Users can now use the up and down arrow keys to navigate through their previous prompts, similar to terminal history navigation. The feature provides persistent storage of prompt history with intelligent deduplication to avoid repeated entries. History is maintained on a per-workspace basis, ensuring that prompts remain contextually relevant to the current project while being shared across different chat sessions within that workspace.

The input history can be configured through the enablePromptHistory option, giving users control over this functionality.

The video below demonstrates the prompt history navigation in action:

As always, the 1.65 release contains much more than described in this article, e.g. the compatibility with VS Code Extensions has been upgraded to API version 1.104.0, support for Node.js 18 has been dropped in favor of Node.js 20+, and numerous bug fixes including improved breakpoint handling, fixed menu actions, and better status bar tooltip handling.

For a complete overview of all changes in this release, please refer to the 1.65 milestone. All these features and improvements (in total 78) were the result of one month of intensive development. Eclipse Theia follows a monthly release schedule. We are looking forward to the next release due next month, stay tuned! To be notified about future releases, follow us on LinkedIn or follow Theia on Twitter and subscribe to our mailing list.

If you are interested in building custom tools or IDEs based on Eclipse Theia, EclipseSource provides consulting and implementation services for Eclipse Theia, for AI-powered tools, as well as for web-based tools in general.

Furthermore, if you want to extend Theia, Theia AI or the Theia IDE with new features or strategically invest into the project, EclipseSource provides sponsored development for Theia, too. Finally, we provide consulting and support for hosting web-based tools in the cloud.

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