Route AI Coding Tasks by Risk: A Free-Tier-First Workflow You Can Actually Measure

Most discussions about AI coding tools start with "which model is best?" I've found that's the wrong first question. The better question is: which of my tasks actually need the strongest model, and which ones don't? In my earlier posts I wrote about building a small evaluation suite for AI coding models and a falsification loop for reviewing AI-generated refactors. This post is the missing piece between them: a routing layer that decides, per task, whether a free-tier model is good enough — and a way to measure whether that decision was right, instead of trusting vibes. The problem: paying frontier prices for boilerplate work When every prompt goes to the most expensive model by default, two things happen: You burn budget on tasks a weaker model handles fine (renaming, boilerplate, docstrings, simple test generation). You never build intuition for where the strong model genuinely matters, because you never see the failure distribution of the cheap one. The fix isn't a blog-post benchmark. It's a per-task routing rule plus a log you can audit weekly. Step 1: Classify tasks by blast radius, not difficulty Difficulty is subjective. Blast radius — what breaks if the output is wrong and you don't catch it — is not. I use three tiers: Tier Task examples Failure cost Default route Low Rename/refactor with compiler backing, boilerplate, doc comments, unit test scaffolding, commit message drafts Caught by compiler/CI in seconds Free/cheap model Medium New function in an existing module, bug fix with a clear reproducer, small migration script Caught by code review or tests, costs an hour Free model first, escalate on failure High Concurrency changes, auth/payment logic, schema migrations on live data, security-sensitive parsing May reach production silently Strongest available model + mandatory human review Two rules make this table work: Escalation is cheap, so bias toward the free tier. If the free model's output fails your checks, you escalate that one task. You lose minut