Sigma is going to announce a new 100-400mm f/5-6.3 DG DN OS lens according to the latest report from Nokishita:
Update - it seems that this lens will be available only for L mount and Sony E mounts. A new Sigma TC-2011 teleconverter and Sigma USB dock UD-11 will also be announced.
"Sigma will announce "100-400mm F5-6.3 DG DN OS" in the near future. "
No other information is available for now. Stay tuned for additional details.