Although PFOA, like PFOS, has been regulated already for several years, the PFOA section was much trickier to construct than the PFOS section, and remains incomplete due to the wording of the definition in Annex A of the Stockholm Convention . The entire node currently contains 25,472 CIDs, but only 789 of these have been included in the "PFOA plus its salts and PFOA-related compounds as defined in Annex A of the Stockholm Convention" section, since the exclusions to the definition are almost impossible to define or automate cheminformatically with existing PubChem functionality. Thus, at this stage, entries that (to the best of our knowledge) meet the definition have been included, and several other sections are included under this node for users to explore other content further. The entries that are included are the selected and updated lists from the Stockholm Convention (80 and 299 CIDs, respectively) plus three PubChem queries covering PFOA and branched isomers (47 CIDs), PFOA, branched isomers and salts (162 CIDs) and the PFOA plus branched isomer substructure query to capture mixtures (546 CIDs). An additional section breaks down the 789 matching PFOA content by annotation categories, such as found in literature (81), use information available (228), safety or toxicity information (41), patent information (401) or recent addition (in 2022 or 2023, 60 entries). This helps find potentially relevant entries among the hundreds of potentially regulated matches. The PFOA exclusions have been included in the node below, with placeholder nodes for content that cannot currently be created with reasonable effort. The halide exclusions have been implemented (currently 26 entries), and the updated indicative list of exclusions (35 CIDs). Polymers are inherently excluded from the tree as it currently covers compound space only, with additional functionality to enable polymer/UVCB inclusion still under active development at PubChem (and thus a potential future extension). The automatic detection of the remaining two exclusion categories, perfluoroalkyl carboxylic and phosphonic acids (including their salts, esters, halides and anhydrides) with ≥8 perfluorinated carbons, plus the perfluoroalkane sulfonic acids (including their salts, esters, halides and anhydrides) with ≥9 perfluorinated carbons has proven tricky. Although it may theoretically be possible to implement these exclusions programmatically, the current wording would require the creation of thousands of lines of custom code or several hundred very inefficient queries which, given the potentially thousands of possible matching entries, would be likewise difficult to check for accuracy and curate accordingly (several attempts at implementing this have been made already and sidelined as currently unviable). This remains an area of development for the PubChem PFAS Tree and a conversation topic with regulators, highlighting the challenges in implementing the current definition into an automated cheminformatics workflow, which will be necessary to update these regulatory lists in a manner scalable to the current numbers of PFAS (millions).