I'm a solo developer running 10+ projects with a multi-model agent setup: Opus 4.8 as the main thread, Fable 5 (2× Opus price) as a decision advisor, Sonnet/Haiku for mechanical subagent work. The question I couldn't answer: which tasks actually deserve the expensive tier, and where was I overpaying?
So I built a routing audit as an opt-in module of my tracing SDK, backfilled ~26,000 traces (34 days) from Claude Code's local session logs, priced them at official list prices, and diffed my stated routing policy against my revealed routing behavior. Everything below is list-price equivalent (I'm on a subscription; API-paying teams see these numbers for real).
Finding 0: your usage history is quietly rewriting itself
Claude Code's resume/compact rewrites session JSONL files. Between two ingest runs, 5 messages vanished from a source file. If your usage numbers come from re-reading live session files (as most usage dashboards do), they drift. An append-only ingest log fixed it — and gave an unexpected validation: my Fable traces reproduce June's export-control suspension window to the hour (1,599 traces on Jun 10, exactly zero from Jun 14–30, resuming Jul 1).
Takeaway: snapshot your telemetry into an immutable store, or you're auditing sand.
