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Introducing a WDM dimension on the top of a TDM PON system is a natural evolution to increase the capacity of an optical access network, and this can also offer additional flexibility options. Several hybrid WDM/TDM PON architectures can be designed, each with a different degree of flexibility, going from fully static, over partially flexible to fully flexible architectures. The more flexible architectures, however, are either more expensive, experience a higher power loss or are less secure. A question that arises is if a fully flexible architecture is really needed, or if a partially flexible architecture already can serve several flexibility advantages, like energy efficiency, network migration and network extensibility. An important assessment parameter is the number of needed wavelengths at a certain network load. For a fully flexible architecture, it is clear that the number of needed wavelengths can be optimally minimized, but how big is the gain of a fully flexible architecture compared to a partially flexible one, and what is the minimum degree of flexibility required to have a significant advantage of the offered flexibility. In this paper we evaluate through simulation different architectural options for a hybrid WDM/TDM PON, in terms of flexibility. For this purpose, we use an underlined well-suited medium access control (MAC) protocol that exploits the offered flexibility in terms of dynamic wavelength allocation.