I'm on ElasticSearch 2.3.1 on OS X. I'm just showing the input and output for 10 but I've duplicated it at 100 and 1000 index operations as well.
Input: last index id is 42721014
Output: last index id is 42721013
{"took"=>1,
"errors"=>false,
"items"=>
[{"index"=>
{"_index"=>"roots_index0",
"_type"=>"root",
"_id"=>"42721005",
"_version"=>1,
"_shards"=>{"total"=>2, "successful"=>1, "failed"=>0},
"status"=>201}},
{"index"=>
{"_index"=>"roots_index0",
"_type"=>"root",
"_id"=>"42721006",
"_version"=>1,
"_shards"=>{"total"=>2, "successful"=>1, "failed"=>0},
"status"=>201}},
{"index"=>
{"_index"=>"roots_index0",
"_type"=>"root",
"_id"=>"42721007",
"_version"=>1,
"_shards"=>{"total"=>2, "successful"=>1, "failed"=>0},
"status"=>201}},
{"index"=>
{"_index"=>"roots_index0",
"_type"=>"root",
"_id"=>"42721008",
"_version"=>1,
"_shards"=>{"total"=>2, "successful"=>1, "failed"=>0},
"status"=>201}},
{"index"=>
{"_index"=>"roots_index0",
"_type"=>"root",
"_id"=>"42721009",
"_version"=>1,
"_shards"=>{"total"=>2, "successful"=>1, "failed"=>0},
"status"=>201}},
{"index"=>
{"_index"=>"roots_index0",
"_type"=>"root",
"_id"=>"42721010",
"_version"=>1,
"_shards"=>{"total"=>2, "successful"=>1, "failed"=>0},
"status"=>201}},
{"index"=>
{"_index"=>"roots_index0",
"_type"=>"root",
"_id"=>"42721011",
"_version"=>1,
"_shards"=>{"total"=>2, "successful"=>1, "failed"=>0},
"status"=>201}},
{"index"=>
{"_index"=>"roots_index0",
"_type"=>"root",
"_id"=>"42721012",
"_version"=>1,
"_shards"=>{"total"=>2, "successful"=>1, "failed"=>0},
"status"=>201}},
{"index"=>
{"_index"=>"roots_index0",
"_type"=>"root",
"_id"=>"42721013",
"_version"=>1,
"_shards"=>{"total"=>2, "successful"=>1, "failed"=>0},
"status"=>201}}]}