The CMMI Institute publishes various comparisons of CMMI documents.
CMMI-DEV Model Comparisons
Comparison of CMMI-DEV, V1.3 to CMMI-DEV, V1.2 shows the complete set of changes to the CMMI-DEV model moving from CMMI Version 1.2 to CMMI Version 1.3.
CMMI-DEV Quick Reference Comparisons
CMMI-DEV Goals-Practices, V1.3 to CMMI-DEV Goals-Practices, V1.2 shows the differences between V1.2 and V1.3 specific goal and practice statements as well as process area purpose statements.
To see comparisons of CMMI-DEV to other models, standards, and methods as well as mappings and other related information, see CMMI Compatibility.