OK so this is interesting (and frustrating). Vikram I couldn’t replicate your results. Regardless of the ‘extendCircular’ input, it would always add a fillet. Looking into this more, 7000 offset is the threshold. Offsetting less than this amount, it is possible to offset a rectangle with square corners. Greater than this amount, it will ALWAYS create the fillets. So it seems this is a units thing. I’ve submitted the issue to Github: https://github.com/DynamoDS/Dynamo/issues/6156
I’m going to try scaling down the geometry, run the offset, and then scale back up.