Clarification on enabling and evaluating 512K context

#3
by pengwenzhi - opened

Hi Granite team,

The model card says Granite-4.2-3B natively supports 128K, with long-context extension to 512K, but the architecture still lists a sequence length of 131072, and the vLLM/SGLang examples do not show how to enable 512K.

Could you clarify the recommended configuration for 512K inference?

  • Is 512K officially supported by the released checkpoint?
  • Does it require any RoPE scaling or other positional-encoding settings?
  • For vLLM, is --max-model-len 524288 sufficient?
  • For SGLang, is --context-length 524288 sufficient?
  • Do you have an official 512K evaluation or launch example?

Thanks!

IBM Granite org

Hi @pengwenzhi thanks for the question! Here are the details on the 128k vs 512k context lengths:

  • All models in the 4.2 family were trained to support 512k context, so for each inference platform, you can simply use the corresponding flag to raise the max context length (no RoPE scaling needed)
  • All models in the 4.2 were benchmarked and evaluated using 128k context, so the default values for each distributed checkpoint format is set to 128k as the maximum verified length

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