GPT-6 Astra vs. Fable 5.1: Performance and Cost Analysis

Benchmark Performance

GPT-6 Astra and Fable 5.1 were evaluated across the eight-task KingBench 3 suite. Astra achieved a 90% score (72/80), while Fable 5.1 scored 92.5% (74/80). Astra demonstrated superior capability in spatial and graphical tasks, specifically the 3D folding table, panda SVG generation, and 3D wristwatch implementation. Both models performed identically on the permutation math problem and the Gemma 2B fine-tuning task. Fable 5.1 outperformed Astra on the elevator simulation, contact lens case, and archery game.

Real-World Project Reliability

In larger, multi-component projects, the performance gap widened significantly. Astra struggled with a terminal-based movie tracker, failing to integrate the TMDB API and producing flickering UI elements. In an Obsidian clone project, Astra failed to initialize the OpenCode SDK agent and generated subpar, overly generic UI components. Fable 5.1 successfully integrated the OpenCode agent and provided more functional, project-specific designs. Astra consistently defaulted to a repetitive aesthetic characterized by green color schemes, card-based layouts, and generic landing-page structures.

Operational Efficiency and Cost

Testing revealed a notable discrepancy in token expenditure and workflow speed. The Astra test suite cost approximately $198 in tokens, whereas the Fable 5.1 suite cost $113, representing a 75% increase in cost for the former. Astra exhibited higher latency on basic tasks and showed an over-reliance on tool calling, even for simple conversational inputs. Fable 5.1 demonstrated better adherence to user instructions and a higher propensity to request clarification when requirements were ambiguous.