Arm was never modeless. Thumb is a separate encoding with different instruction semantics and Jazelle ran Java bytecode. Both of them need a special branch instruction to enter. What they don't have is legacy modes like real, v8086 or native 16/32 protected that have no reason to exist when a CPU in long mode can run 16 and 32 bit code (in compatibility sub mode) just fine.
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Arm was never modeless. Thumb is a separate encoding with different instruction semantics and Jazelle ran Java bytecode. Both of them need a special branch instruction to enter. What they don't have is legacy modes like real, v8086 or native 16/32 protected that have no reason to exist when a CPU in long mode can run 16 and 32 bit code (in compatibility sub mode) just fine.