The special form declare is available, but all declarations are currently ignored by the interpreter and the compiler, including special declarations.
It may be fairly easy to add proper handling of special declarations to the byte code compiler, but adding it to the interpreter will cut speed unless the code is rewritten in the spirit of macro displacement.
The function proclaim is available. Currently only special proclamations have an effect. There is no portable way to take back a special proclamation.
Macros for the special forms locally and the are available. They currently ignore declaration and type information.