In this article we study base change of Poincaré series along a quasi-complete intersection homomorphism
φ
:
Q
→
R
\varphi \colon Q \to R
, where
Q
Q
is a local ring with maximal ideal
m
\mathfrak {m}
. In particular, we give a precise relationship between the Poincaré series
P
M
Q
(
t
)
\mathrm {P}^Q_M(t)
of a finitely generated
R
R
-module
M
M
to
P
M
R
(
t
)
\mathrm {P}^R_M(t)
when the kernel of
φ
\varphi
is contained in
m
a
n
n
Q
(
M
)
\mathfrak {m}\,\mathrm {ann}_Q(M)
. This generalizes a classical result of Shamash for complete intersection homomorphisms. Our proof goes through base change formulas for Poincaré series under the map of dg algebras
Q
→
E
Q\to E
, with
E
E
the Koszul complex on a minimal set of generators for the kernel of
φ
\varphi
.