What GapGPT actually billed per model, with dates and evidence, so a
later price rise can be compared with what it was. gpt-4.1-mini and
gpt-4o-mini were re-checked from the 852 recorded calls in
docs/benchmarks/2026-09-26-tutor-model: every call equals the official
OpenAI per-token price or less (input cache), none more.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
