🤯 Gemini 4 Carbon is a BEAST! Watch It Handle Complex Builds with Multiple AI Agents

Introduction

Gemini 4 Carbon is now publicly available. Google first limited it to cyber defenders in its Fairwind program, then opened it up. Here’s where you can use it today:

• The paid Gemini API, through Google AI Studio, Android Studio, GitHub Copilot, Google Antigravity, and Gemini for Business

• The Gemini app and AI Mode in Search, for Google AI Ultra subscribers ($100/month)

There’s no free API tier for Carbon, so you’ll need a paid API project or an Ultra subscription to try it. It currently sits at #1 on the Artificial Analysis Intelligence Index v5.0 with a score of 59, Claude Opus 5.5 is right behind at 58.

I ran these tests with early access, but the prompts below work on any of those surfaces now.

Test 1: Coding, Browser OS with a GTA-Style Game

This was the hardest possible first test. I asked Gemini 4 Carbon to build a fully interactive browser-based operating system, with a playable GTA-style game inside it.

What I asked for:

• A desktop with draggable windows, a taskbar, and animated wallpapers

• Working apps: file manager, terminal, calculator, notes, settings

• A playable 3D open-world driving game inside the OS, with AI pedestrians, moving traffic, and a police pursuit system

• Day/night lighting, adjustable gravity, keyboard shortcuts, sound effects

Here’s the full prompt if you want to try Gemini 4 Carbon yourself:

Act as a senior full-stack engineer and game developer.

Build a fully interactive browser-based operating system using React, TypeScript, Tailwind CSS, and Three.js.

The operating system should include:

1. A desktop with draggable, resizable windows, a taskbar, an app launcher, and animated wallpapers.
2. A working file manager that supports folders, text files, and persistent local storage.
3. A terminal with basic commands, a calculator, a notes app, and a settings panel.
4. A playable 3D open-world driving game inspired by classic sandbox games, using original assets and designs.
5. Driving physics with acceleration, braking, steering, and vehicle collisions.
6. NPC pedestrians, moving traffic, interactive vehicles, and a basic police pursuit system.
7. Dynamic day and night lighting, adjustable gravity, and an in-game camera mode.
8. Keyboard shortcuts, sound effects, and smooth transitions between applications.

Technical requirements:
- Use reusable React components and a modular project structure.
- Keep desktop and game state separate.
- Use local storage for persistent user settings and files.
- Optimize 3D rendering and avoid unnecessary memory usage.
- Handle application errors without crashing the entire desktop.
- Make the operating system usable at common desktop resolutions.

Development process:
- First, plan the architecture and dependencies.
- Build the desktop and verify window management.
- Implement the applications and file persistence.
- Develop the 3D game with working controls and collision detection.
- Run the project and test the main interactions.
- Fix reproducible bugs before presenting the final result.

Deliver a complete runnable project, setup instructions, and a short report explaining what works, what failed, and what still needs improvement.

Don't use static mockups to replace functional features.

Gemini 4 Carbon built an interactive browser desktop with animated wallpapers, a file manager, and working apps. Its GTA-style game lets me drive a police car, use weapons, and change gravity. Lower gravity even sends cars flying. Traffic solved, apparently!

The core features worked. But some NPCs walked on water, a few visual effects looked glitchy, and both the desktop and the game needed more polish before you’d call them finished.

→ Honest summary: Solid first-pass prototype. Way more functional than most tools produce in one shot. Still needs debugging and cleanup before it feels like a real product.

Test 2: Recreating 3D Jerry’s Apartment

After the coding test, I wanted to see how Gemini 4 Carbon handles detailed 3D environments.

This time, I gave it harder tasks: recreate Jerry Seinfeld’s apartment from the show, with accurate floor plan, furniture placement, and interactive features.

This is a good benchmark because anyone who’s watched the show has a strong sense of what it should look like, so errors are obvious.

What I asked for:

• Accurate floor plan: living room, kitchen, hallway, entrance

• Furniture: sofa, TV, kitchen cabinets, dining table, shelves

• Small details: posters, books, collectibles

• Interactive features: doors that open and close, doorbell, lighting controls

• Two camera modes: first-person and orbit

If you want to test Gemini 4 Carbon’s 3D skills, try this prompt:

Act as a senior 3D artist and Three.js developer.

Recreate Jerry's apartment from Seinfeld as an accurate and interactive 3D environment using Three.js.

Use the supplied reference images to match the original floor plan, furniture, and room layout.

1. Floor Plan and Architecture
- Recreate the living room, kitchen, hallway, and entrance.
- Match room sizes, wall positions, doors, and openings.
- Make sure all rooms connect correctly.
- Check that the hallway and door positions make sense in real life.

2. Furniture and Interior Details
- Recreate the sofa, TV, kitchen cabinets, dining table, and shelves.
- Match the size and position of each object.
- Add small details such as posters, books, collectibles, and decorations.
- Use custom 3D shapes when basic shapes aren't enough.

3. Materials and Lighting
- Use suitable materials for wood, fabric, glass, and metal.
- Add realistic shadows and room lighting.
- Create different lighting settings, including a warm evening mode.
- Keep the original look of the apartment.

4. Interactive Features
- Add first-person and orbit camera controls.
- Make doors open and close in the correct direction.
- Add a doorbell interaction.
- Allow users to switch lighting settings and hide the interface.
- Add clickable labels for important objects.

5. Technical Requirements
- Use Three.js with clean and reusable code.
- Separate the room, furniture, lighting, and interaction systems.
- Optimize 3D models and rendering performance.
- Keep object sizes and positions consistent.

Before building, study the reference images and create a detailed floor plan.

After building, check the room layout, door directions, furniture positions, and camera views.

Fix major layout problems before adding small decorations.

Deliver a complete 3D environment that runs in a browser.

The best result I’ve seen on this particular challenge. Gemini 4 Carbon nailed the overall floor plan more closely than other models I’ve tested. The living room, kitchen, and hallway were recognizable.

The interior also had many small details, including a Macintosh computer, Superman figure, New York Mets cap, and Porsche posters. You could open doors, ring the doorbell, and switch between two lighting modes.

There were still a few mistakes. Jerry’s door and Kramer’s door both opened in the wrong direction, and the hallway geometry wouldn’t make sense in a real building.

These are the kinds of errors that show up in every AI-generated 3D environment right now. Spatial reasoning is still the weak point.

→ Honest summary: The closest floor plan accuracy I’ve seen from any model on this test. The interactive features were a nice touch. The spatial errors are real but relatively minor.

Test 3: Multi-Agent Build, SplashBash 3D Pool Party Game

This was the most interesting test.

Gemini 4 Carbon has multi-agent coordination capabilities, where multiple specialized AI agents work on different parts of the same project in parallel, then hand off their work to be integrated.

I asked Gemini 4 Carbon to use this multi-agent approach to build a complete 3D pool party game from scratch. 5 five agents I specified:

• Environment agent: backyard, pool, houses, garden, furniture, water effects

• Character agent: four playable characters (Hank, Sky, Chad, Betty) with animations

• Gameplay agent: three game modes (Crowd Favorite, Solo vs AI, Local Multiplayer) plus a Free Dive sandbox

• AI opponents agent: different difficulty levels and movement behaviors

• UI and Audio agent: character select screen, HUD, music, sound effects, telemetry display

Here’s the prompt I used:

Act as a senior game development team. Use Agent Swarm to build a complete, playable 3D pool party game.

PROJECT GOAL:

Create a colorful backyard pool party game with a lively environment, funny characters, and multiple game modes.

Use multiple specialized agents to work on different parts of the project. Each agent should have a clear role, and all agents must follow the same visual style and game design.

AGENT 1: ENVIRONMENT DESIGN
- Build a detailed backyard with a swimming pool, houses, garden, and outdoor furniture.
- Add realistic water, lighting, shadows, and environmental details.
- Create a fun summer party atmosphere.

AGENT 2: CHARACTERS
- Create four playable characters: Hank, Sky, Chad, and Betty.
- Give each character a unique appearance and personality.
- Add smooth movement, jumping, swimming, and interaction animations.

AGENT 3: GAMEPLAY
- Build three game modes:
  1. Crowd Favorite.
  2. Solo mode against three AI party rivals.
  3. Local multiplayer with players sharing one screen.
- Add a Free Dive sandbox mode.
- Implement scoring, round progression, and clear win conditions.

AGENT 4: AI OPPONENTS
- Create opponents with different movement styles and behaviors.
- Make their actions respond to the player's position and game events.
- Adjust difficulty based on the selected game mode.

AGENT 5: UI AND AUDIO
- Create a character selection screen and gameplay menu.
- Add a clean HUD with scores and game information.
- Include background music, party sounds, and interactive sound effects.
- Add a live telemetry display during gameplay.

FINAL REQUIREMENTS:
- Coordinate all agents and integrate their work into one project.
- Keep the visual style consistent across every part.
- Test all game modes, character controls, and interactions.
- Fix major gameplay bugs and improve visual quality.
- Deliver a complete, playable game rather than static mockups.

The result was surprisingly good! Gemini 4 Carbon built SplashBash 3D, a pool party game with four characters: Hank, Sky, Chad, and Betty. It included solo mode against three AI opponents, local multiplayer, and Free Dive.

The telemetry panel was also interesting. It showed each agent’s status, frame rate, and water simulation performance. You could also change AI difficulty and lighting settings.

After another update, Gemini 4 Carbon added more houses, improved the graphics, and added a Wii Sports-style telemetry display. There was even a boombox playing music!

The entire build and update took less than an hour.

Where it fell short: the final result still doesn’t match the visual polish of Fable 5.2. The characters and environment are fun, but they look more like a playful prototype than a finished game.

Comparison: Gemini 4 Carbon vs Claude Fable 5.2

I also compared Gemini 4 Carbon with Claude Fable 5.2. I ran both models on the same 3D sailing ship prompt to get a direct comparison.

Both built detailed ships. The difference was in the visual execution:

• Fable 5.2: more realistic water, natural lighting, better overall material quality

• Gemini 4 Carbon: more colorful and stylized, but the ocean looked flat and the water texture repeated too visibly

Twitter tweet

Verdict on this specific test: Fable 5.2 wins on visual realism. Carbon’s result was good, but the gap in rendering quality was noticeable.

This is one test on one type of task. Carbon’s multi-agent build speed is a genuinely different strength that Fable 5.2 doesn’t match in the same way.

The Honest Takeaway

Here’s where Gemini 4 Carbon actually stands after three tests:

The case for Carbon:

• Multi-agent coordination is genuinely fast and impressive, with complex builds coming together in under an hour

• Strong at detailed environment generation

• Currently #1 on the Artificial Analysis Intelligence Index, though only by a single point over Opus 5.5, and most benchmarks are still vendor-reported, so treat that ranking with appropriate skepticism

The honest caveats:

• No free tier. Carbon is paid-only, through a paid Gemini API project or a Google AI Ultra subscription ($100/month) for the Gemini app and Search

• Visual quality in 3D work is behind Fable 5.2

• Bugs and polish issues appear in complex projects, same as every other model at this complexity level

• “Agent Swarm” isn’t an official Google feature name. It’s multi-agent coordination, which Antigravity supports but doesn’t brand that way

Is it worth trying when it opens up? Yes, especially if you’re doing complex multi-part builds where parallel agents would save time. Just don’t expect every result to be perfect on the first pass. That’s true of every frontier model right now.

Conclusion

After testing coding, 3D generation, and Agent Swarm, Gemini 4 Carbon has shown some impressive results. It can build playable games, recreate detailed 3D environments, and coordinate multiple AI agents on one project.

I was most impressed by its Agent Swarm feature. Building a 3D game with multiple agents in under an hour is quite impressive. However, Claude Fable 5.2 still has an edge in visual quality and realism.

Gemini 4 Carbon is definitely worth trying, especially if you enjoy building things with AI. Just don’t expect every result to be perfect on the first try. Some bugs and extra editing are still part of the process.

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