Major Architectural Changes

Replit Agent 4 evolves four core pillars of the building experience: design, collaboration, artifact types, and the planning-building workflow. Each feature has been rethought from the ground up rather than simply replaced, resulting in a faster and more collaborative development experience.

Design Canvas Replaces Standalone Design Mode

The new Design Canvas is an infinite, always-available workspace that replaces Agent 3's separate Design Mode tab. The canvas displays two content types side-by-side: interactive artifact previews (running versions of your actual app) and design mockups (lightweight visual prototypes for rapid exploration). Developers can now resize frames, edit inline, preview across multiple screen sizes, and manipulate designs without triggering full agent processing loops.

Crucially, the Design Canvas works with all artifact types—web apps, mobile apps, slide decks, data visualizations—whereas Agent 3's Design Mode was limited to web apps only. Mockups remain visual prototypes without server backends; conversion to a full artifact is required for publishing.

Unified Collaboration Model

Agent 4 eliminates the fork-and-merge collaboration model in favor of a shared project workspace. All team members work in the same project simultaneously, each with their own chat thread for planning with the Agent. A shared Kanban board displays tasks across four columns: Drafts, Active, Ready, and Done, providing real-time visibility into team progress.

Agent-assisted merging handles conflict resolution automatically, removing the manual friction point that plagued Agent 3. Git tracking continues under the hood with complexity abstracted away.

Parallel Planning and Execution

The sequential plan-then-build workflow evolves into plan-while-building. Teams can now open new chat threads for planning while active builds continue running independently. New tasks execute in isolated environments (exact copies of the current project) and move through the Kanban board without touching the main project until explicitly approved. Parallel execution is safe: conflicting file changes are flagged and resolved through the Agent.

Backward Compatibility

Existing Agent 3 projects remain fully functional. New projects unlock Agent 4 features including the Design Canvas, shared collaboration, and parallel task execution. Multi-artifact projects are not yet compatible with migrated projects but are in development.