[{"key":1,timestamps:{history:[{time:10},{time:9},{time:8},]}},{"key":2,timestamps:{history:[{time:6},{time:5},{time:4},]}}]

db.collection.aggregate([{$match:{key:1}},{$project:{"timestamps.history":{$filter:{input:"$timestamps.history",as:"item",cond:{$and:[{$lt:["$$item.time",10]},]}},},}}])