The 30-year-old has agreed a two-year contract and becomes Exeter's sixth new recruit for next season.
Horstmann has been a Worcester player since 2005, having moved to Sixways from Harlequins.
"We are a team that is looking to improve and keep strengthening all the time, and we feel Kai is a very experienced Premiership performer," Exeter head coach Rob Baxter said.
"He is a guy who I have had a very close look at, and I like the way he plays.
"I think he will fit in very well for us. He is mobile and athletic, reads the lineout well and the basics of his game stand up very well."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
$29.99
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.
