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Not quite, it needs 51% of hashing power in order to be safely backwards compatible with non-upgraded nodes, however it's always safe with upgraded nodes. That's the reason BIP9 has a 95% activation threshold.

Note this is by far not the first soft fork Bitcoin has done. P2SH, CSV, and CLTV for example were also soft forked in. The original design even included 10 blank opcodes designed for soft forking in features.

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> 51% of hashing power in order to be safely backwards compatible with non-upgraded nodes, however it's always safe with upgraded nodes

Yes, what I was pointing out is that in a soft-fork there is a risk of an eventual re-org, whereas in a hard-fork there is not. It's a minor risk, but it exists.

I also believe that any non-SegWit miners will be pushed out of the network using the mechanism I described. It would be pretty easy to trick them into mining invalid blocks.

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