Developer weighs GPT 5.6 vs Fable 5 for coding in Codex
A developer working on an AI research codebase had been using Fable 5 High for design and debugging, then recently tried inside Codex. Fable 5 felt fast and fluid, while GPT 5.6 seems to do more thorough hardening of the codebase but can run 4-5 hours without finishing a task. In that time the developer burned through 100% of their , then used another 40% after it reset.
Even running at 1.5x speed, GPT 5.6 still feels slow. The developer is asking others whether the wait is worth it, how to use GPT 5.6 in Codex more efficiently, and how it compares to Fable 5.
Key points
- Fable 5 High is praised for being fast and responsive
- appears to harden code more thoroughly but can run 4-5 hours without completing a task
- Feels slow even at 1.5x speed
- Burned 100% of , then another 40% after reset
- Asking the community for tips on using GPT 5.6 in Codex efficiently