What Changed from Replit Agent 3 to Agent 4

Replit Agent 4 redesigns four pillars of the build experience. Design, collaboration, the scope of what you can build, and the way planning and implementation work have all changed together.

The biggest change is that Design Mode is gone and Design Canvas is now the center. You no longer need to switch between separate tabs — you can start from Design on the home screen, request a design via chat, or bring an existing app page into the canvas and edit it directly.

Design Canvas works with every Artifact type on an infinite canvas, offering live preview and direct-manipulation tools. Two things appear together on the canvas:

• Artifact previews: runnable versions of the actual app
• design mockups: lightweight visual prototypes for quick exploration

Here you can resize frames, make inline edits, change colors, and preview across mobile / tablet / desktop screens. However, a mockup isn't a complete app with a server attached, so it must first be converted into an App before it can be deployed.

The collaboration model has also changed significantly. Agent 3's fork-and-merge model is gone, and now everyone works within the same project. Each collaborator plans with the Agent in their own chat thread, and tasks can be batched and worked on simultaneously.

Tasks are shown on a shared Kanban board across four columns: Drafts, Active, Ready, Done. Changes are still tracked with Git, but the Agent now helps with the merge process, so manual conflict resolution is no longer required.

The build flow has also shifted from plan-then-build to plan-while-building. While the main build is running, you can open a new chat to plan, and that plan runs in an isolated environment that acts like an exact clone of the current project.

• The main project is left untouched until the user explicitly approves the change.
• Parallel execution of multiple tasks is safely possible.
• If tasks touch the same files, the system detects the conflict and the Agent resolves it.

In short, Agent 4 isn't just a feature addition — it's a rewrite of the entire build experience. Design is more flexible, collaboration is more immediate, and planning and implementation are no longer sequential.