With a mongosh connect to a server that supports timeseries collections and run something similar to the following commands (output provided for context): > db.createCollection("timeseries_123", { timeseries: { timeField: "a" } }); { ok: 1 } > // expecting the next command to return an Error > db.runCommand({ collMod: "timeseries_123", validator: { required: ["a"] } }); { ok: 1 } > // this one just confirms that validator is not actually set which is expected > db.getCollectionInfos().find(coll => coll.name === 'timeseries_123') { name: 'timeseries_123', type: 'timeseries', options: { timeseries: { timeField: 'a', granularity: 'seconds', bucketMaxSpanSeconds: 3600 } }, info: { readOnly: false } }