Best coding context length for DeepSeek V4.1 Flash: 300K–500K, default 400K
The author argues 1M context is overkill for most coding tasks and the sweet spot for DeepSeek V4.1 Flash is 300K–500K, recommending a 400K default with manual compaction since agents count max output toward the limit.
I've been trying to figure out the best context length for DeepSeek V4.1 Flash when coding, and the honest answer is that 1M is too much for most tasks. From everything I've read, the sweet spot seems to be somewhere between 300K and 500K, and it makes sense. Past that, the model gets slower, every message costs more, and it starts paying less attention to what's actually in front of it. Having a 1M window doesn't mean the model can really use all of it. One thing that surprised me is that some agents count your max output toward the limit before compacting. So if you set 500K with 128K reserved for output, it'll actually start compacting closer to 370K. My plan is 400K as the default, and compacting by hand when the task changes instead of waiting for it to fill up.