IMPORTANT:

PrimeGrid will be switching to a preferences-based method for setting up multi-threading in the near future.
If you are using app_config.xml (probably to set up multi-threading) it's going to stop working when the multi-threading system goes live. If you want your app_config.xml to continue working, you should make modifications now that will allow it to work both before and after the change.

Only LLR projects are affected.

Every <app_version> block for an LLR project should be duplicated, with the duplicate having a <plan_class>mt<plan_class> line added to it. For example, this is the before and after for ESP, set up for 4 threads:
<app>
  <name>llrESP</name>
  <fraction_done_exact>1</fraction_done_exact>
  <report_results_immediately>1</report_results_immediately>
</app>
 
<app_version>
  <app_name>llrESP</app_name>
  <cmdline>-t 4</cmdline>
  <avg_ncpus>4</avg_ncpus>
</app_version>
 
<app_version>
  <app_name>llrESP</app_name>
  <plan_class>mt</plan_class>
  <cmdline>-t 4</cmdline>
  <avg_ncpus>4</avg_ncpus>
</app_version>
You can do this today, and the original app_version block will continue to work. Once we install the new multi-tasking, that app_version block will be ignored and the second app_version block for the mt plan class will take over. At that point, most people can erase app_config.xml, or at least the parts for LLR projects, and start using the multi-threading controls on the website.

I don't have an exact time yet for this change, but it won't happen in August. I'm hoping for early September.