I think you're confusing the GH4 with the A7s. This is true for the A7s, but not the GH4. As jax says, the GH4 does record 8-bit 4:2:0 4K internally.
Pretty sure Bold (the OP) has already taken delivery of the GH4, so this is moot. That said, I thought seriously about selling my GH4 and...