Auto Model vs Picking Your Own: We Tested Kilo Code's Router on a Backend Build

The pace of new model releases has made “which model should I use for this?” a real problem. Just in the last month we saw Claude Sonnet 5, Claude Fable 5, GPT-5.6, Grok 4.5, Gemini 3.6 Flash, and Kimi K3, and keeping track of which one is best (and cheapest) for planning versus implementation is now a task on its own.

Auto Model is Kilo Code’s answer to that: you pick a tier (frontier, balanced, efficient, or free) and the router selects the underlying model per request. We ran an experiment to see whether letting the router decide can hold up against manually picking models by hand.

TL;DR: On this experiment, all three setups produced functionally identical services (each passed the same 29 of 30 logic checks). The differences were cost and contract adherence, not correctness. The Auto pipeline (frontier to plan, efficient to implement) cost $1.26 total against $2.90 for GPT-5.6 Sol everywhere and $2.47 for Claude Sonnet 5 everywhere, and it was the only run that matched the fixed API contract exactly.

Why we stopped using one model for everything

Over the last few posts we have kept measuring the same thing. When we compared Claude Fable 5 against GPT-5.5, the two models split on planning but implemented the same plan almost interchangeably, and the cheaper model built the same passing service for well under half the cost. When we compared GPT-5.6 Sol against Fable 5 on planning, the gap that used to exist between flagships on implementation was gone. The conclusion we keep arriving at is that you do not need the most expensive model for every step. Frontier models are worth their price on the hard reasoning (planning, architecture), and a cheaper model is usually enough to build a plan that is already decided.

The problem is that acting on this by hand is tedious. You have to remember which model is strong at what, switch models when you change modes, and re-check your assumptions every time a new release lands. Auto Model moves that decision into the router. You…