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Silent re-pricing, alias re-routing, tokenizer drift and expiring intro prices don't throw a single error — they just change your invoice. The Drift Audit reads your last 90 days of provider usage exports and shows you exactly what moved, and what it cost you.

Early access — we onboard in waves. No endpoint change, read-only on your usage exports.

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Four ways a bill drifts with zero errors

All four happened in the last 14 months. Provider deprecation emails cover none of them — those announce retirements, with notice, to the account owner. Drift is what happens without an announcement.

alias re-routing

The model name survives. The price doesn't.

In May 2026, xAI retired eight model slugs but kept them resolving — requests to grok-code-fast-1 silently routed to a flagship model at flagship prices. No 404, no deprecation error. The bill and the output quality both changed overnight.

in-place re-pricing

Same name, new price at GA

Gemini 2.5 Flash left preview with its output rate moving from $0.60 to $2.50 per million — a 4× change under an unchanged model name. Teams that budgeted on preview pricing found out on the invoice.

tokenizer drift

Per-token price constant, tokens +30%

Claude's tokenizer from 4.7 onward produces roughly 30% more tokens for the same text. Headline per-token prices never moved — the bill did. No price page will ever show you this one.

intro-price expiry

The discount has a date

Claude Sonnet 5 runs at $2/$10 introductory pricing until 31 August 2026, then becomes $3/$15 — a +50% step most teams haven't calendared. Dated price events like this are exactly what monitoring is for.

How the audit works

  1. Export your usage. Anthropic's audit CSV, OpenAI's usage API report, or your invoice lines. Nothing to install, no endpoint change, no key to share.
  2. We cross it against our verified registry. Per-model prices and lifecycle status, each figure checked against the vendor's own page — the same registry behind our public benchmark.
  3. You get the drift report. Silently re-priced models in your traffic, aliased or deprecated slugs you still call, tokenizer exposure, and upcoming dated price events — each with the dollar impact on your actual volume.

Questions

Isn't this what provider deprecation emails are for?

Those emails announce scheduled retirements, with 60 days to 12 months of notice — and they go to the account owner, not the engineer who owns the integration. None of the four drift patterns above comes with an email, because none of them is a retirement.

Do I have to route my traffic through you?

No. The audit is read-only on usage exports you already have. Teams that route through VerticalAPI's gateway get the same detection continuously, per request — but the audit requires no integration at all.

What does continuous monitoring add over a one-time audit?

Drift is recurring: new GA re-pricings, new aliases, the next tokenizer change, the next intro price with an expiry date. Monitoring watches your model mix against the registry and alerts you before the invoice does.