Yep that happens with coding agents sending a very large system prompt. And also when later tool calling feed it large files or diffs. But with the M3 ultra the prefill speed is almost 500 t/s that is quite into the very usable zone. With M3 max you need a bit more patience but it works well and as it emits the think process if you use the pi agent you don't wait: you read non censored chain of though. I posted a video on X yesterday using it with my m3 max. It spills tokens at a decent speed.