Rule 497(e)

File No. 333-191151

CALAMOS ETF TRUST 

(the “Trust”)

Calamos Timpani Active SMID Growth ETF 

(the “Fund”) 

Supplement dated September 18, 2026 

to the Fund’s Prospectus and Statement of Additional Information, each dated June 22, 2026, as amended

This supplement updates certain information contained in the Fund’s Prospectus and Statement of Additional Information and should be attached to each document and retained for future reference.

Capitalized terms not defined herein have the same meaning as in the Fund’s Prospectus and Statement of Additional Information.

The Fund previously disclosed that shares of the Fund were not yet available for purchase. The Fund is pleased to announce that shares of the Fund will be available for purchase beginning September 21, 2026. On September 21, 2026, the Fund’s shares will be listed and begin trading on the Texas Stock Exchange LLC.

This Supplement is not an offer to sell or a solicitation of an offer to buy shares of the Fund.

Please retain this supplement for future reference.