The cost decline for a given level of performance does tend to slow over time
Even in their tests, there are big drops in 2026 models, and recent ones.
A much more comprehensive and easy test is to follow this benchmark suite (AAi). Its a mix of medium/hard benchmarks, with bias for agentic coding. (sorry for url dump) artificialanalysis.ai/?endpoints=openai_gpt-5-2-c…
Opus 4.8 (may 2026), by far best model at the time, gets equaled by deepseek 4 pro (july 31) and 4.1 flash (sept 10th) at less than 1/100th the cost. MiMo 2.6 pro (sept 21) is even cheaper and beats opus 4.8 scores by a wide margin. sonnet 4.6 max to gpt luna high is also a 99% cost drop in a short time for lower performance level models.