Qwen3.8 27B

User reports a performance issue with Qwen3.8 27B on an M3 Max 48GB, comparing mlx-serve against LM Studio. The mlx-serve run used the ddalcu/Qwen3.8-27B-MLX-Serve-4bit model at 128k context and achieved 59.6 tok/s decode (54.9-60.2) and 196.4 tok/s prefill, while LM Studio with the Swift-1.5-Qwen3.8-27B-Splash model reached 96.4 tok/s decode (89.1-96.8) and 210.5 tok/s prefill. Both runs used speculative decoding (MTP/draft active). The mlx-serve run showed a 42.1% slowdown under sustained load (59.6 to 34.5 tok/s over 8m 4s), and context scaling was worse than LM Studio at longer contexts (37.2 vs 76.5 tok/s at ~4.2k, 35.6 vs 60.5 at ~8.2k, 34.6 vs 57.6 at ~16.3k). The user reports mlx-serve is 38% slower on decode overall and up to 51% slower at ~4.2k context, while being 18% faster on TTFT.