GPT-5 is likely to be even more expensive to train and operate than GPT-4.

The claim is that GPT-5 would cost more than GPT-4 both to train and to operate. Judge it at GPT-5's release and the months after. Training cost can be shown by compute or dollar estimates from OpenAI or credible third parties (for example Epoch AI or major press reporting). Operating cost can be shown by OpenAI's per-token API prices for comparable tiers, or by reported inference cost per query or in total. Compare against GPT-4 at launch. True: credible evidence shows GPT-5 cost more than GPT-4 to train, and also more to operate. Mostly true: training clearly cost more, but the operating-cost evidence is mixed. For example, list prices fell while total or per-query inference compute rose. Mixed: one of the two (training or operating) was clearly more expensive and the other was clearly cheaper. Mostly false: training cost was about the same or unclear, and operating cost was lower. False: credible evidence shows GPT-5 was no more expensive than GPT-4 to train and was cheaper to operate. Lower per-token API prices for GPT-5 than for GPT-4 at launch count as evidence of cheaper operation unless credible reports show higher underlying serving costs.

Set before the research began.

1. E1 Notes on GPT-5 training compute Epoch AI (Substack) · 13 October 2025

   “Our best guess: GPT-5 was trained on ~5e25 FLOP total, including both pre-training and reinforcement learning. That would be more than twice as much as GPT-4 (~2e25 FLOP), but less than GPT-4.5 (>1e26 FLOP).”

2. E2 Introducing GPT-5 for developers OpenAI · 7 August 2025

   “GPT‑5 is priced at $1.25/1M input tokens and $10/1M output tokens”

3. E3 Why GPT-5 used less training compute than GPT-4.5 (but GPT-6 probably won’t) Epoch AI · 26 September 2025

   “It’s likely that the total compute for developing GPT-5 was higher than for GPT-4.5, if we also account for the compute for running experiments.”

4. E4 Why GPT-5 used less training compute than GPT-4.5 (but GPT-6 probably won’t) Epoch AI · 26 September 2025

   “One more reason that OpenAI likely chose to focus on scaling post-training without increasing pre-training compute for GPT-5 is to reduce inference costs.”

Epoch AI's best estimate is that GPT-5 was trained on about 5e25 FLOP in total, more than twice GPT-4's roughly 2e25 FLOP [E1], so independent evidence shows training cost more. The operating-cost evidence does not settle the question. E2 gives GPT-5's API prices ($1.25 per 1M input tokens and $10 per 1M output tokens), but no evidence item gives GPT-4's launch prices to compare against. E4 says OpenAI may have shaped GPT-5's training partly to reduce inference costs, but it gives no measured cost figure and does not compare against GPT-4. Since training clearly cost more and the operating-cost side is unclear, the criteria point to mostly true.