1. There will be changes in fees and permanent message size limit in 1.7. They will take effect in the 1.7 hard fork, in very early January 2016.

2. These changes will break any application that has hardcoded fees of 1 NXT, or uses permanent messages exceeding 160 bytes.

3. *snip* ALL API USERS CAN, AND ABSOLUTELY MUST START UPDATING THEIR CODE NOW. DO NOT WAIT UNTIL 1.7 STABLE IS RELEASED *snip* START UPDATING TO 1.6.2, USE SERVER-SIDE FEE CALCULATION, AND EITHER SWITCH TO PRUNABLE MESSAGES, OR MAKE SURE PERMANENT MESSAGE SIZE DOES NOT EXCEED 160 BYTES.

4. To repeat. Do not wait until 1.7.1 stable *snip* THIS IS THE ADVANCE NOTICE.

Technical questions about the transition should be discussed here: https://nxtforum.org/core-development-discussion/adapting-client-side-code-to-the-fee-changes-planned-for-1-7/