The two published figures reconcile in only one way, and which way changes what you copy. Price a hundred requests under the old setup: all strong, at about $0.0145 a call, $1.45 [9]. Now read the 81% as the share that *attempts* the cheap model first, with 15% of those escalating [3][11]. That is 81 cheap calls, 12.15 strong retries, and 19 requests pinned to the strong tier: $0.565 per hundred, a 61% cut. Read it as the share *finally served* by the cheap answer and it lands: 95.3 cheap attempts, 14.3 escalations, 4.7 requests sent straight to strong, $0.409 per hundred, a 71.8% reduction [20]. Under that second reading, the `ForceStrong` and `alwaysStrong` short-circuits at the top of the router cover under 5% of production traffic [17][20]. The post does not say which reading it means.
The cheap side does check out against the posted prices. Three thousand input tokens at $0.20 per million is $0.0006; 700 output at $1.20 is $0.00084; total $0.00144, which is the post's $0.0014 [19]. The strong model is never named in the excerpt, so its $0.0145 per call is a number you cannot audit. Flattened across the same 3,700 tokens it implies roughly $3.92 per million [21]. If your two tiers sit closer than that, the break-even algebra is the first thing to redo.
Escalation costs $0.0159 against $0.0145, about 10% more than going strong directly [10], which is why the money question closes fast and the gate becomes the whole design. The `Gate` type returns the reason an answer cannot be trusted, or empty string to accept it [13]. The first default gate is `SchemaInvalid`: the response had to be JSON matching a schema, and wasn't [14]. That check is free CPU. A gate that needs a model to score the output re-imports the exact per-request tax that killed the first design: another call, another 300ms [5].
The classifier failed on something worse than its cost, though. Length correlated with the shape of a request and not its difficulty: "Fix the timezone bug" needs everything you have, while "Summarise the following 4,000-word RFC" is long and trivial [7]. The post calls the first of those eleven characters; it is twenty [22]. The point survives the miscount. Difficulty is a property of the work, so the only honest way to learn it is to do the work [8].
The error handling is the part I would keep verbatim. When the cheap call errors, the router falls through to strong, because a 429 or a timeout is availability and not quality. When the strong call errors after escalation, it returns the cheap answer: degraded rather than failed [15]. That second line is a policy decision hiding in a return statement. It means a strong-tier outage reaches users as slightly worse answers instead of errors, and the only place it shows up is the escalate and accept counters, which is why those carry a reason label [18]. The escalation call also resends the original request, not the original plus the cheap draft; the author flags that as failure mode four and the one people get wrong, and the excerpt stops before the other three arrive [16][4].
This transfers if your traffic really is mostly titles, diff summaries and extracted fields [2], and if your gates can be assertions rather than judgments. Both are checkable before you write the router.
