Is the native Android BLE implementation synchronous in nature?

Samsung recently published a "migration"-document on the same page I linked in my question. They exactly answer my question while comparing the new native BLE API with the Samsung BLE API:

The synchronous nature of the stack and F/W hasn’t been affected. That is, if we call for example, writeCharacteristic for a particular characteristic, if it returns true, the next call to any BluetoothGatt or BluetoothGattServer method should be done after the onCharacteristicRead callback is received. This is because the stack is designed to support and process only one GATT call at a time, and if, for example, you call writeCharacteristic or readCharacteristic of any characteristic soon after the first one, it is ignored.