Thank you for your question regarding compatibility with COBOL 6.3. We would like to inform you that version 2.3 of Telon is no longer supported. As such, we cannot provide any guarantee that COBOL 6.3 is compatible. Telon 5.1 however does support COBOL 6.4 and lower. Please see the Telon 5.1 compatibility matrix here: https://ftpdocs.broadcom.com/WebInterface/phpdocs/0/MSPSaccount/COMPAT/TLN.HTML