ecCodes is and evolution of GRIB-API and will replace it in the future.
GRIB-API is entirely included in ecCodes (ecCodes-GRIB-API) without any change to its Fortran 90, Python, C interfaces and command line tools. Therefore the migration from GRIB-API to ecCodes-GRIB-API will not affect the user software and will be managed in installation and linking phases. Neverthless, very significant changes in the library have been performed to implement the encoding of different types of messages and in particular for BUFR.
To be confident that ecCodes-GRIB-API behaves as GRIB-API we are performing a set of test. At the moment all the stadard tests are passing without problems. One important aspect of the library is performance and we are continously checking that ecCodes-GRIB-API performs at least as GRIB-API. In the latest version the difference in performance is not significant. ecCodes-GRIB-API is performing as GRIB-API and in some tests it is slightly better.
Some more tests are needed to be fully confident that ecCodes-GRIB-API can replace GRIB-API in an operational environment, but we don't have experience at the moment of problems with ecCodes-GRIB-API. We strongly advise the users to do their own migration tests and send feedback to software.support@ecmwf.int.