We implement a slightly different version of classical GCPN. We represent an incomplete molecule by a graph G ≡ (V, E) where V ∈ R nxd contains the d features for each of the (maximum of n) atoms (nodes) and E ∈ {0, 1} nxn is the adjacency matrix. We don't store bond order information since atom-types can be used to determine it. A key difference in our model is that we use a changing action space. Unlike traditional GCPN , SPOTLIGHT already picks the first atom (the focal atom) to which we will add our next atom. The action space for each state is the list of allowed atom-types (according to forcefield rules) to connect to the focal atom. The size of this list can vary. Once the model picks an atom-type, the positioning and cyclization are also taken care of by the traditional method where we complete a cycle if the new atom falls within bonding distance of another atom with a free valency.