Frontier LLM prices didn't move for 5 months. In August, they moved three times, and one lab tripled its rate.

On August 1 I published a report whose headline finding was that frontier LLM API prices are structurally sticky . Across 40 daily readings of an equal-weight index of ten flagship models — one per lab — not one lab had ever changed the price of an existing model. Every move in the index had come from a new model replacing an old one. August made that sentence false in three weeks. Here's what moved, why the index still ended the month lower , and what happened 72 hours after the cutoff that dwarfs all of it. The month in one table The index is the equal-weight average of ten flagships' blended price per million tokens (3 parts input to 1 part output, list prices as printed on the vendor's own pricing page). Date What happened Index ($/Mtok) Aug 1 Opening level $4.39 Aug 4 Alibaba's slot: Qwen3.7-Max → Qwen3.8-Max ($3.75 → $3.00 blended) $4.32 Aug 16 DeepSeek V4 Pro repriced : flat $0.435/$0.87 → peak $1.32/$3.96 (+264% blended) $4.46 Aug 21 GPT-5.6 Sol repriced : $5/$30 → $4/$20, labelled promotional (−29%) $4.14 Sep 1 Closing level $4.14 Net for the month: −5.7% . Since the first reading on February 23: −9.4% . Three other flagship handovers happened in August (Muse Spark 1.1 → 1.2, Grok 4.5 → 4.6, GLM-5.2 → 5.3) and moved nothing, because each successor kept its predecessor's list price. That's the pattern I described in August. The two bolded rows are the pattern breaking. Move 1: DeepSeek turned "list price" into a schedule Until 16:00 UTC on August 16, DeepSeek V4 Pro billed a single flat rate: $0.435 in / $0.87 out. Then the pricing page split it in two: Peak (01:00–04:00 and 06:00–10:00 UTC): $1.32 / $3.96 Off-peak (every other hour): exactly half — $0.66 / $1.98 The index tracks the peak rate as the list price. Two reasons. DeepSeek defines off-peak as a discount from peak, not the other way round, so peak is the published number. And a caller who doesn't schedule around the clock needs a ceiling, not a floor. But note that even the off-peak rate ($0.99 ble