Importing from Instruments.app
There are two supported methods for importing from Instruments.app: importing Time Profiler .trace files, and importing via deep copy.
After recording either a Time Profiler profile or an Allocations profile, select the root row of the table view. Then select "Edit -> Deep Copy" from the main menu.
This will copy a tree containing aggregate statistics about the profile onto your clipboard. Now visit https://www.speedscope.app and paste. Note that this method only carries aggregate statistics, rather than time-ordered samples, so you the time ordered view and the left heavy view will look similar.
WARNING: At time of writing, import of Instruments 10 files seems to be buggy at best. See https://github.com/jlfwong/speedscope/issues/196
To record a time profile using Instruments.app, first select "Time Profiler" from the list of profiling templates.
Select the target you want to profile.
Click the record button.
When you're done recording, hit the stop button.
Then save the profile as a .trace file.
If you drag and drop the resulting file into speedscope, it should load the profile.
At time of writing, selecting the file via "browse" or running speedscope /path/to/Instruments.trace won't work. See https://github.com/jlfwong/speedscope/issues/97