Eclipse Theia 1.64 Release: News and Noteworthy

We are happy to announce the Eclipse Theia 1.64 release! The release contains in total 60 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 happy to announce that the Call for Presentations is now OPEN for the 2025 TheiaCon! TheiaCon is an 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 2024. Submit your proposal today to be a speaker and get registered!

The Theia 1.64 release is the first release candidate for the next community release 2024-08. So if you plan to adopt the next community release, please verify the 1.64 release and report important issues for your use case!

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 1.64.

Eclipse Theia 1.64: Selected features and improvements

In the following, we will highlight some selected improvements in the new release. As usual, we cannot mention all 60 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.

Promote Theia IDE AI Features to Beta

Since the alpha release of the AI-powered Theia IDE in March 2025, we’ve made tremendous strides in expanding and refining our AI capabilities for end users of the IDE. It’s important to note that this beta promotion applies only to the AI features within the Theia IDE for end users. The underlying AI framework, Theia AI, has been a stable release since March 2025 and can already be adopted by developers to build fully custom AI-native tools and IDEs.

With Theia 1.64, the AI-powered Theia IDE (built on Theia AI) is officially graduating from alpha to beta status! This milestone represents months of development, testing, and refinement based on community feedback. Our journey has brought exciting new capabilities including Task Context Support for more efficient and structured AI coding; rich image support allowing users to communicate visual problems directly to AI assistants; an AI-driven E2E testing agent that can automatically test web applications without writing a single line of test code; enhanced custom agent creation capabilities that enable users to create specialized AI assistants for domain-specific tasks without writing backend code; and expanded LLM support, including cutting-edge models like Claude 4 Sonnet and Opus.

With each enhancement, we’ve maintained our commitment to transparency, user control, and LLM independence, allowing developers to use any AI model they prefer while maintaining full visibility into data sharing and AI interactions. Finally, we have continued to work on compatibility with emerging standards such as MCP.

The beta release represents a more stable, feature-rich toolset for end users of the Theia IDE. For developers looking to build AI-native tools from scratch, the Theia AI framework remains a stable, production-ready foundation that can be adopted independently of the IDE.

Support for Model Aliases and Default Models

As detailed in our recent article, Theia AI supports any large language model (LLM), whether it’s from OpenAI, Anthropic, Google, or others - a core strength that ensures maximum flexibility for users integrating AI into their development workflows. However, this flexibility comes with a trade-off: initial setup requires users to configure which model is used where. Especially for advanced scenarios - such as using multiple LLM providers in parallel - users previously had to configure the model on a per-agent basis, which could become cumbersome and error-prone.

With Theia 1.64, we introduce model aliases, a new concept that addresses both challenges. Instead of assigning a specific model to each agent, users can now select a model alias (e.g. default/code) that represents a particular intent or purpose, such as code generation, summarization, or general tasks (see screenshot below). These aliases can be centrally configured to point to a specific model or to a prioritized fallback chain of models. Changing the model used for an alias automatically updates all agents using that alias - no need to configure each agent individually.

Selecting model aliases for different purposes and agents.

This concept also improves the out-of-the-box experience for new users. All built-in agents are now preconfigured to use default aliases. Each alias has a corresponding model chain defined, and Theia AI automatically selects the first model in the chain that is ready to use (i.e. has a valid API key configured). For example, if a user adds only an Anthropic API key, Theia AI will automatically select Claude for all agents using the default/code alias. This means agents will be functional immediately after a key is provided - without requiring manual configuration per agent.

The AI configuration view has been extended with a new Model Aliases tab (see screenshot below), which provides a visual overview of all aliases, the fallback chains, and each model’s readiness state. Models without a configured API key are disabled and display a helpful tooltip. Users can also override the fallback chain by assigning a specific model to an alias, if desired.

The new Model Aliases configuration view with fallback chains and model status.

This foundational feature simplifies setup, improves maintainability in multi-model environments, and ensures that both new and advanced users can get started—and stay productive—with significantly less manual configuration.

Tool Functions for launching Apps

Theia AI 1.64 includes new tool functions for interacting with existing run configurations: listLaunchConfigurations, runLaunchConfiguration, and stopLaunchConfiguration. These functions enable agents to start and stop applications based on the launch configurations available in the workspace.

When made available to an LLM—either through the chat or the system prompt—these functions allow the agent to control applications directly. For example, the AppTester agent could now independently list available launch configurations, start the target application, perform actions within it, and stop it once testing is complete.

In the accompanying demonstration video, the AppTester agent uses these functions to automate launching and stopping an application under test, showing how this integration can streamline automated workflows and testing scenarios.

3-Way Merge Editor

Theia now includes a 3-way merge editor for resolving Git merge conflicts directly within the IDE. This feature is based on the merge editor from VS Code, with minor adjustments for integration into Theia.

When a file with merge conflicts is opened from the Source Control view, users can switch from the default text editor to the merge editor using the floating “Resolve in Merge Editor” button. The merge editor displays the conflicting changes alongside the resulting output, making it easier to review and decide which changes to keep. Once all conflicts are resolved, the “Complete Merge” button saves, stages, and closes the merge editor.

In the demo video, we put the AI terminal assistant in the AI-powered Theia IDE to unconventional use—asking it to generate a local merge conflict just so we could show off the new editor. Proof that if you give us AI, we’ll find a way to apply it literally anywhere.

This initial version provides the core functionality for handling merge conflicts in a structured and visual way, streamlining the resolution process and reducing the risk of errors compared to manual edits.

As always, the 1.64 release contains much more than described in this article, e.g. the compatibility with VS Code Extensions has been upgraded to API version 1.102.3, and we improved the prompt for task context creation.
For a complete overview of all Theia AI updates in this release, please refer to the collecting epic for 1.64. All these features and improvements (in total 60) 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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