Just to confirm that it's probably not a garbageCollect problem, I could not reproduce in latest Squeak trunk. I did not use Zinc because it's too much difficult to install in Squeak and just replaced with WebClient. STON is available (installed thru Squit/Squot git support):
``` | aJson anArray | aJson := WebClient httpGet: 'https://data.nasa.gov/resource/y77d-th95.json'. Array streamContents: [ :aStream | 400 timesRepeat: [ aStream nextPutAll: (STON fromString: aJson content). Smalltalk saveSession ] ]. ```
The resulting image file is 540Mbytes long.