ISO expansion on 7D is only for ISO 12,800. But ISO 6400 is native for this sensor so I'm not sure why Auto ISO does not include it as it's upper max. Maybe they think 6400 is not good enough and don't want customer complaining when they get a little bit of grain when shooting with Auto ISO.
I emailed Canon support about it to see if they can address in in a FW update but I got the generic answer of how to increase it manually.
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