7 July 2026 · 5 min read
The AI Spend Autopsy is a one-off report. You connect read-only keys, we analyse 30 days of usage across your providers, and you get an itemised list of savings with the arithmetic shown. It costs £99. If we find less than £99 a month in savings, you get the £99 back.
This post walks through a real autopsy — run on Halcyon Labs, the fictional company that ships as TokenLedger's demo dataset — so you can see exactly what the findings look like and how each number is derived. Halcyon spends about £4,473 a month across OpenAI and Anthropic. The autopsy found £1,114.78 a month, roughly 25% of spend.
| Finding | Confidence | Monthly saving | | --- | --- | --- | | Stop paying for retries | HIGH | £213.81 | | Right-size frontier-model workloads | MED | £488.20 | | Cache the repeated prompt prefix | MED | £269.95 | | Batch the nightly workload | MED | £142.82 | | Total | | £1,114.78 |
For every key, TokenLedger computes an hourly spend baseline from the trailing month. On 6 July, Halcyon's evals-nightly key spiked to 23.6x its hourly baseline. Nothing shipped that day and no dataset grew. That shape — one key, one night, an order of magnitude above baseline — is a retry loop: a failing request being resent, each attempt billed in full, until a timeout gives up.
The formula: saving = spike excess × 0.8. The spike excess is what the key spent above its baseline during the event — £267.26. We apply a 0.8 recovery factor because some elevated spend during an incident is legitimate (genuine reprocessing, partial successes). That gives £213.81.
Why is this monthly? Because the loop is in a nightly job and the bug does not fix itself. Until someone adds backoff and a retry cap, every transient failure re-runs the same billing event. Fixing it once removes the class of spend, not one instance of it.
This is HIGH confidence: the spike is directly observed in the billing data, and the only assumption is the recovery factor.
One of Halcyon's keys sends gpt-4.1 a high volume of requests with long inputs and very short outputs — the signature of classification, not generation. Labelling a support ticket does not need a frontier model. gpt-4.1-mini handles short-output classification at roughly one fifth of the price.
The formula: saving = spend × price delta × 0.4. The identified classification traffic is £1,525.63 a month. The price delta between gpt-4.1 and gpt-4.1-mini is 0.8 — the mini model costs 80% less per token. We then apply a 0.4 adoption factor: we assume only 40% of the traffic actually migrates, because some requests will turn out to need the larger model and no migration ever reaches 100%. £1,525.63 × 0.8 × 0.4 = £488.20.
MED confidence: the traffic shape is observed, but "this workload will perform acceptably on the smaller model" is an assumption you should verify with an eval before switching.
Two of Halcyon's keys send the same multi-thousand-token system prompt on every single request — and the usage data shows zero cached tokens. Prompt caching is opt-in on Anthropic, and nobody opted in. Cached input tokens are billed at a 90% discount, so an identical prefix resent thousands of times a day is the cheapest fix on this list: it is a one-line change.
The formula: saving = input cost × cache discount × 0.6. The input-token cost attributable to the repeated prefix is £499.91 a month. The cache discount is 0.9. The 0.6 adoption factor covers cache misses: entries expire between requests, prefixes occasionally change, and not every request window keeps the cache warm. £499.91 × 0.9 × 0.6 = £269.95.
MED confidence: the repetition and the zero cache reads are observed; the realised hit rate is an estimate.
Halcyon runs jobs at 02:00 every night — embedding refreshes and evals — through the standard synchronous API, at full interactive rates. Nobody is awake. Nobody needs the answer in 800 milliseconds. Both major providers offer a batch API at a 50% discount for workloads that can wait up to 24 hours, and a job scheduled for 02:00 is the definition of a workload that can wait.
The formula: saving = night spend × 0.5 × 0.5. The recurring night-window spend is £571.28 a month. The first 0.5 is the batch discount. The second 0.5 is the eligibility assumption: only half the nightly volume is assumed to migrate, since some jobs feed morning dashboards with tighter deadlines. £571.28 × 0.5 × 0.5 = £142.82.
Every finding carries HIGH, MED or LOW confidence, and the labels have rules.
Halcyon's £1,114.78 is one HIGH finding plus three MED findings. No LOW findings are in that number.
The autopsy costs £99, once. If the HIGH and MED findings total less than £99 a month in savings, tell us within 30 days and we refund the £99 in full. On the demo dataset the findings came to 11x the fee; on real accounts with more than one engineer and a retry loop, the ratio is usually not close.
Connect read-only keys, wait a few minutes, read the arithmetic. That is the product.