DebugActive

For Thread objects, a boolean DebugActive is defined at offset 0x03 in the DISPATCHER_HEADER from as far back as Windows Server 2003, having previously been deeper into the KTHREAD. Windows 7 made bit fields of it, though later versions have kept them only for the x64 builds:

Mask Definition Versions
0x01
BOOLEAN ActiveDR7 : 1;
6.1 only (x86);
6.1 and higher (x64)
0x02
BOOLEAN Instrumented : 1;
6.1 only (x86);
6.1 and higher (x64)
0x04
BOOLEAN Minimal : 1;
6.3 and higher (x64)
 
BOOLEAN Reserved2 : 4;
6.1 only (x86);
6.1 to 6.2 (x64)
BOOLEAN Reserved : 3;
6.3 only (x64)
BOOLEAN Reserved4 : 3;
10.0 and higher (x64)
0x40
BOOLEAN UmsScheduled : 1;
6.1 only (x86);
6.1 and higher (x64)
0x80
BOOLEAN UmsPrimary : 1;
6.1 only (x86);
6.1 and higher (x64)