On Tue, Jun 16, 2015 at 1:36 PM, Brad Jorsch (Anomie) <bjorsch@wikimedia.org> wrote:
Note that formatversion=2 is still considered slightly experimental, in that backwards-incompatible changes like this can still happen. If you see any other changes like this that should be made, please report them!

Starting in 1.26wmf11, the following changes will be made in the output from meta=siteinfo when formatversion=2 is in use:
  • Output from siprop=namespaces will be an array, rather than an object indexed by namespace number. See T102645.[1]

This was reverted in https://gerrit.wikimedia.org/r/#/c/219514/ . The output of siprop=namespaces will not change in 1.26wmf11.