Claude Code: React Turns AI Terminal into Game Engine

"Most people's mental model of Claude Code is that 'it's just a TUI', but it should really be closer to 'a small game engine'," said Shihipar. He said that on every frame, Claude Code constructs a UI state, calculates the layout, converts it into a screen representation, compares it with the previous frame, and generates the minimal ANSI instructions needed to update the terminal. "We have a ~16ms frame budget, so we have roughly ~5ms to go from the React scene graph to ANSI written." In December, Shihipar explained the technical cause of terminal flickering.

Terminals contain a viewport and a scrollback buffer, and when content exceeds the viewport, rendering occurs offscreen. "Unlike regular CLI tools that print output and exit, Claude Code is a long-running interactive UI. We redraw our viewport dozens of times per second," he said.

To address this, Anthropic rewrote the rendering system to diff individual terminal cells and emit only minimal ANSI escape sequences instead of full redraws. Full redraws are now used only when necessary, reducing flickering by roughly 85%. Shihipar said the team considered using an alternate screen mode, similar to tools like Emacs, which would allow full control over scrolling and rendering.