Messages that contain only GSM03.38 seven-bit characters have a maximum limit of 1,600 characters. Messages that are longer than 160 characters will be split into multiple messages, with each message consisting of a maximum of 153 characters.
Messages containing one or more UCS-2 16-bit Unicode characters have a maximum limit of 737 characters. Messages longer than 70 characters will be split into multiple messages, with each message consisting of a maximum of 67 characters. The list of Unicode characters can be found here: https://unicode-table.com/en/#control-character
Multi-unit messages are automatically stitched back together and delivered as a single message in countries where mobile networks support long message concatenation.