This depends on how you plan to use the machine... but Qwen-flash-next is right at the top of what a 128GB Apple Silicon can do.
QFN with 4bit quantization will run "comfortably" with all weights in memory and a 128k context on a 128GB machine. On M5 Max w/ 128GB, that will give about 75 tok/sec (using oMLX with MTP enabled). It spits out text much faster than I can read.
However, this truly uses all the RAM. You'll have like 8-12GB left for the OS and apps, which isn't really enough to actually use the machine as a workstation while the model is loaded. But it would work fine as an inference server with Opencode running on your laptop. (Hence, "how you plan to use it?")
Alternatively, you can offload QFN's n-gram table to SSD (this is just a settings option in oMLX), which drops generation speed on the same machine to ~60-65 tok/sec (assuming the model lives on the internal SSD) and reduces memory usage to ~90GB with even a large context. That leaves plenty of RAM to use the Studio as your main workstation. Also, you may run much longer contexts because of the extra memory headroom.
Second alternatively, you can use oMLX's expert offloading feature to keep 50% of experts in memory (with n-gram offloading also). This reduces the RAM footprint to a little over 32GB + context. Offloading the experts drops generation speed to around 20-25 tok/sec on the same machine as above, but it would allow you to comfortably run on a 64GB machine, while still using it as a workstation.
I have tested the 50% expert offload case on an M1 Max / 64GB, and the inference speed is only a little slower (more like 18-20 tok/sec) than M5 Max / 128GB because in both cases the bottleneck is SSD read bandwidth and the GPU is spending a lot of time idle.
One last thing: GLM 5.3-flash doesn't use an n-gram table, so you can't use that trick to reduce memory footprint. You'd need to use expert offloading to make it fit a 128GB machine. Since it has over twice as many active parameters as QFN (which doubles the required SSD read bandwidth), my guess is that a 128GB Studio would not be much faster than your current setup for that model.