Also note that they've changed the branding from A1 to M6g, making ARM a peer of Intel and AMD. So their 2020 lineup will probably be:
M6: Intel Ice Lake-SP
M6a: AMD Rome
M6g: ARM Graviton2
That's hugely impressive. I don't remember any ARM processors beating Skylake in single threaded workloads before. To pull ahead by 40% seems almost unbelievably good. (I understand Skylake can clock much higher than 3.1GHz, but I guess cloud instances are mostly around this value due to the high core counts.)
No, the Graviton and Graviton2 processors do not have SMT. Each vCPU (or logical processor, for a bare metal instance) is a core.
"Each vCPU is a thread of either an Intel Xeon core or an AMD EPYC core, except for A1 instances... Each vCPU on A1 instances is a core of an AWS Graviton Processor."