This article establishes cutoff thermalization (also known as the cutoff phenomenon) for a class of generalized Ornstein–Uhlenbeck systems $$(X^\varepsilon _t(x))_{t\geqslant 0}$$
(
X
t
ε
(
x
)
)
t
⩾
0
with $$\varepsilon $$
ε
-small additive Lévy noise and initial value x. The driving noise processes include Brownian motion, $$\alpha $$
α
-stable Lévy flights, finite intensity compound Poisson processes, and red noises, and may be highly degenerate. Window cutoff thermalization is shown under mild generic assumptions; that is, we see an asymptotically sharp $$\infty /0$$
∞
/
0
-collapse of the renormalized Wasserstein distance from the current state to the equilibrium measure $$\mu ^\varepsilon $$
μ
ε
along a time window centered on a precise $$\varepsilon $$
ε
-dependent time scale $$\mathfrak {t}_\varepsilon $$
t
ε
. In many interesting situations such as reversible (Lévy) diffusions it is possible to prove the existence of an explicit, universal, deterministic cutoff thermalization profile. That is, for generic initial data x we obtain the stronger result $$\mathcal {W}_p(X^\varepsilon _{t_\varepsilon + r}(x), \mu ^\varepsilon ) \cdot \varepsilon ^{-1} \rightarrow K\cdot e^{-q r}$$
W
p
(
X
t
ε
+
r
ε
(
x
)
,
μ
ε
)
·
ε
-
1
→
K
·
e
-
q
r
for any $$r\in \mathbb {R}$$
r
∈
R
as $$\varepsilon \rightarrow 0$$
ε
→
0
for some spectral constants $$K, q>0$$
K
,
q
>
0
and any $$p\geqslant 1$$
p
⩾
1
whenever the distance is finite. The existence of this limit is characterized by the absence of non-normal growth patterns in terms of an orthogonality condition on a computable family of generalized eigenvectors of $$\mathcal {Q}$$
Q
. Precise error bounds are given. Using these results, this article provides a complete discussion of the cutoff phenomenon for the classical linear oscillator with friction subject to $$\varepsilon $$
ε
-small Brownian motion or $$\alpha $$
α
-stable Lévy flights. Furthermore, we cover the highly degenerate case of a linear chain of oscillators in a generalized heat bath at low temperature.