Is GPT-5.6 Sol Better Than Claude Fable 5?

This video compares two AI coding agents, GPT-5.6 Sol and Claude Fable 5, by having each build the same React Native habit tracker app using Expo. It focuses on whether the cheaper GPT-5.6 Sol can match the quality and functionality of the more expensive Fable 5.

I show the entire process of running GPT-5.6 Sol with high reasoning effort on my MCP server, testing the app on a physical iPhone, and comparing it side-by-side with the Fable 5 version. This is for developers curious about AI coding agents’ practical capabilities and cost-effectiveness.

What's inside

Recap of Claude Fable 5’s habit tracker app
Using GPT-5.6 Sol with high reasoning effort on the same project
Setting up and running the Expo project with GPT-5.6 Sol
GPT-5.6 Sol’s app icon generation and image 2.0 support
Building the app architecture and handling errors during development
Testing core features: onboarding, reminders, notifications, and UI interactions
Widget implementation and fixing container background issues
Side-by-side comparison of GPT-5.6 Sol and Claude Fable 5 apps on a physical device

Recap of Claude Fable 5’s habit tracker app

Claude Fable 5 previously built a full-featured habit tracker app with reminders, a native widget, a heat graph showing consistency, and haptics. It was production-ready but very expensive, costing up to $50 per million tokens. This cost makes it impractical for many developers despite the high quality.

The app included native components and good UX, demonstrating Claude Fable 5’s advanced coding skills. However, the high token cost motivated testing a cheaper alternative.

Using GPT-5.6 Sol with high reasoning effort on the same project

GPT-5.6 Sol costs about 40-50% less per token than Fable 5. To test if cheaper means worse, I ran GPT-5.6 Sol with extra high reasoning effort on the exact same MCP server, project, and prompt plan used for Fable 5.

I gave GPT-5.6 Sol full access to the codebase and used my MCP server’s high-quality agent skills and code patterns tailored for React Native and Expo. This setup ensures a fair comparison focused on output quality and app functionality.

Setting up and running the Expo project with GPT-5.6 Sol

I used Expo to build the app because it’s the best framework for cross-platform React Native apps. The video skips initial setup covered in the Fable 5 video but shows opening the GPT desktop app, creating a new Expo project folder, and adding the app icon skill.

Inside the GPT desktop app, I ran commands to install the skill and then pasted the full prompt to let GPT-5.6 Sol build the entire app from scratch, including naming, app icon, and personality.

GPT-5.6 Sol’s app icon generation and image 2.0 support

The app icon was generated using the app icon skill, which recently gained support for GPT image 2.0. I liked the icon GPT-5.6 Sol created, and it appeared correctly on the device.

This shows GPT-5.6 Sol can handle image generation tasks integrated with coding, improving the app’s polish without manual design work.

Building the app architecture and handling errors during development

GPT-5.6 Sol took about 35 minutes to build the initial app version, loading tools, reading files, and consulting Expo widget documentation. It stopped the server after generating code, which I liked because it avoids orphaned processes.

I restarted the Expo server manually with and opened the app on my iPhone. The first launch showed an error due to the stopped server, but after restarting, the app ran smoothly.

Testing core features: onboarding, reminders, notifications, and UI interactions

The app’s onboarding screen supports light/dark mode and a skip option. Enabling reminders triggers native permission requests with explanations, providing a good user experience.

The home screen handles empty states well. I tested loading sample data, toggling habits, long-press reordering, and editing. The UI uses native XPUI components and includes haptics and animations on interactions.

Some minor UI issues appeared, like items going outside containers and awkward keyboard dismissal, but these matched issues in Fable 5 and are fixable with follow-up prompts.

The widget initially had a container background API issue, identical to Fable 5’s widget problem. I prompted GPT-5.6 Sol again to fix it, which took about 16 minutes.

After the fix, multiple widgets worked simultaneously on the home screen, though one view remained slightly broken. Overall, the widget functionality was solid and comparable to Fable 5.

Side-by-side comparison of GPT-5.6 Sol and Claude Fable 5 apps on a physical device

Finally, I showed both apps running side-by-side on my iPhone. Both used my agent skills and had similar icons and native UI components.

The home screens looked clean and functional on both. The video invites you to judge which app looks better, highlighting that GPT-5.6 Sol delivered a comparable product at a significantly lower cost.

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