<<Disclaimer: Verify this information before applying it to your situation.>>

Bob's Red Mill xanthan gum is accepted by the Star-K of Baltimore even
though the package has a Square-K symbol instead of Star-K.

Ener-G (www.ener-g.com) xanthan gum and tapioca starch are approved by
Kof-K (the Kof-K is on the labels as well).

Also, the O-K confirmed that tapioca flour needs no kosher supervision,
but tapioca starch does.

Thanks -R.