@samaaron has added a batch of HiHat samples to the source code of Sonic Pi on github which will be available in the next version. To whet your appetite I have built a version including these and here they are put through their paces.
If you are interested the program I used to play them is here but of course it will only work when you have a Sonic Version including the new samples
Nice! When will the next version be available?
Not sure when the next version will come out. That’s up to @samaaron. The latest public release is still 4.3 released on Sept 30th 2022, but there have been two interim Tech-Preview of version 5 releases for patreon supporters since then, the latest on March 14th 2023. This featured the inclusion of Hydra as a visualiser built in to Sonic Pi. There are also a lot of under the hood changes to the operation of Sonic Pi. At present the only way to include the hat samples is to build from source, although you could download the samples and use them as external samples with version 4.3