In this paper, we explore a sharp phase transition phenomenon which occurs for L p -Carleman classes with exponents 0 < p < 1. These classes are defined as for the standard Carleman classes, only the L ∞ -bounds are replaced by corresponding L p -bounds. We study the quasinormsfor some weight sequence M = {M n } n of positive real numbers, and consider as the corresponding L p -Carleman space the completion of a given collection of smooth test functions. To mirror the classical definition, we add the feature of dilatation invariance as well, and consider a larger soft-topology space, the L p -Carleman class. A particular degenerate instance is when M n = 1 for 0 ≤ n ≤ k and M n = +∞ for n > k. This would give the L p -Sobolev spaces, which were analyzed by Peetre, following an initial insight by Douady. Peetre found that these L p -Sobolev spaces are highly degenerate for 0 < p < 1. Indeed, the canonical map W k, p → L p fails to be injective, and there is even an isomorphismCommunicated by Loukas Grafakos. , . . . , f (k) ) acting on the test functions. This means that e.g. the function and its derivative lose contact with each other (they "disconnect"). Here, we analyze this degeneracy for the more general L p -Carleman classes defined by a weight sequence M. If M has some regularity properties, and if the given collection of test functions is what we call ( p, θ)-tame, then we find that there is a sharp boundary, defined in terms of the weight M: on the one side, we get Douady-Peetre's phenomenon of "disconnexion", while on the other, the completion of the test functions consists of C ∞ -smooth functions and the canonical map f → ( f, f , f , . . .) is correspondingly well-behaved in the completion. We also look at the more standard second phase transition, between non-quasianalyticity and quasianalyticity, in the L p setting, with 0 < p < 1.