This has been my impression.

The underlying LiteRT-LM framework used in the edge gallery does support the MTP drafters for the smaller models, but according to:

https://developers.google.com/edge/litert-lm/models/gemma-4

> Note: LiteRT-LM supports E2B and E4B models today, with support for larger models coming soon.

So even Google aren't shipping MTP support for the 26B and 31B models yet.