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 blended) is 82% above the old flat price. This wasn't a discount scheme layered on the old price. It was a 3x increase with a discount window attached. If you run DeepSeek workloads and can batch them: 10:00–01:00 UTC is a long off-peak window. If you can't, your V4 Pro bill roughly tripled in mid-August and the vendor did not send you an email about it. Move 2: OpenAI's cut, with an asterisk On August 21 GPT-5.6 Sol went from $5/$30 to $4/$20 — $11.25 → $8.00 blended, −29%. It's the first list-price cut by any constituent in the index's history. The asterisk is a sentence that appeared on the pricing page the same day: "GPT-5.6 Sol's promotional pricing is available at least through November 21, 2026." That's a floor, not a reversion date. OpenAI publishes no date on which the price goes back up. The index takes list prices as printed, so the cut is in — but if you've modelled Sol at $4/$20 past November 21, that input is contingent on a sentence, and the sentence can change. Two of the ten flagships now publish a list price that's really the top of a range: one has a time-of-day schedule under it, the other has a promo clock over it. Why the cheapest GPT-4-class model didn't get more expensive (yet) The other line I track is the floor: the cheapest model that clears a fixed capability bar (GPQA Diamond ≥ 70, externally measured — roughly GPT-4-class reasoning). It's the deflation story; it fell 17x between March and July. In August it did not move. It stayed at $0.113 per million tokens, set by DeepSeek V4 Flash since July 25. Here's the thing. On August 16 DeepSeek also raised its own V4 Flash peak rate, from $0.14/$0.28 to $0.44/$1.32 — $0.175 → $0.66 blended, 3.8x. The model setting the floor got nearly four times more expensive from its maker, and the floor didn't budge. That's because the floor reads the cheapest listed price for a base model across every host that serves it, and DeepInfra kept serving V4 Flash at $0.09/$0.18. So the cheapest GPT-4-class token on Sept