# Building Apps with Fable, Opus, and Sonnet: The Results Speak Volumes > Source: > Published: 2026-07-15 10:10:43+00:00 # Building Apps with Fable, Opus, and Sonnet: The Results Speak Volumes In an intriguing test of Claude coding models, Fable 5 outperformed Opus 4.8 and Sonnet 5 in building a full-featured app from a specification prompt. The experiment underscores the key role model selection plays in AI-driven development. Imagine building an app in a single breath. That's what Fable 5 achieves with its coding prowess. Recently, three [Claude](/glossary/claude) models, Fable 5, Opus 4.8, and Sonnet 5, were pitted against each other with a real-world test: crafting an expense tracker app from a spec. The goal? Evaluate which model excels performance, efficiency, and cost. ## Head-to-Head: Claude Models Compared In this experiment, Fable 5 proved its mettle by completing a production-ready app with all five features at the first go. A single prompt was all it took. This isn't a partnership announcement. It's a convergence of coding efficiency and AI capability. Opus 4.8, while not as swift as Fable 5, managed to deliver most features quickly. It did, however, stumble on a CSV export/filtering bug, necessitating an additional prompt for corrections. Meanwhile, Sonnet 5 lagged, requiring multiple prompts to address several oversights including category filter connections, CSV headers, date formatting, and mobile responsiveness. ## What This Means for Developers The AI-AI Venn diagram is getting thicker. For developers, the choice of model isn't merely about picking the quickest solution. It's about aligning the model's strengths with task complexity. Fable 5 shines with intricate multi-table specifications. Opus 4.8 strikes a balance for mid-tier tasks. Sonnet 5, despite its shortcomings, fits the bill for simpler feature implementations. But here's the pointed question: In a world where precision and speed are important, can developers afford the extra time and costs associated with less efficient models? The [compute](/glossary/compute) layer needs a payment rail, and the wrong choice could bottleneck entire projects. The author's revised routing strategy underscores a critical takeaway. Prioritize Fable 5 for complex tasks. Use Opus 4.8 as a middle ground. Reserve Sonnet 5 for the straightforward. The best model hinges on task complexity, not a one-size-fits-all label. ## The Future of AI-Driven Coding We're building the financial plumbing for machines, and these model comparisons are more than academic exercises. They're shaping how AI integrates into real-world software development. In this test, Fable 5 didn't just win. It redefined expectations for agentic performance in code generation. If agents have wallets, who holds the keys? As AI models continue to evolve, the choice of tool could be as impactful as the code they write. Selecting the right model could mean the difference between effortless deployment and costly rework. Get AI news in your inbox Daily digest of what matters in AI.