Hi Dror, Molecular surfaces make sessions very large. Even if you hide the molecular surface with the toolbar it is still present and undisplayed as a submodel of your structure so it goes into sessions. You can close molecular surfaces with "surface close". If that is not the issue you would need to give a specific example, like open 1abc and save test.cxs generates a session of size N Mbytes. Tom

On Aug 31, 2021, at 2:04 PM, Dror Noy via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:

Hi Recently, ChimeraX on my Mac (macOS Catalina) started saving very large session file. Regardless of the size of the pdb file I load - the session file is 124 MB even for small 2-3 MB pdb files. I’d appreciate any help. Thanks Dror

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