  We consider a time-dependent $\mathcal{O}(1/G)$ deformation of pure de Sitter
(dS) space in dS gravity coupled to a massless scalar field. It is the dS
counterpart of the AdS Janus deformation and interpolates two asymptotically dS
spaces in the far past and the far future with a single deformation parameter.
The Penrose diagram can be elongated along the time direction indefinitely as
the deformation becomes large. After studying the classical properties of the
geometry such as the area theorem and the fluctuation by a matter field, we
explore the algebraic structure of the field operators on the deformed
spacetime. We argue that the algebra is a von Neumann factor of type
II$_\infty$ for small deformations, but there occurs a transition to type
I$_\infty$ as the deformation increases so that the neck region of the deformed
space becomes a Lorentzian cylinder.
