# Release History
source: https://developer.mastercard.com/mdes-customer-service/documentation/release-history/index.md

Alert: **Please note that the encryption functionality for the Search API is currently not available in the Sandbox environment. We recommend that customers perform their encryption testing in the MTF environment. This will help in identifying any potential issues and ensure that the encryption works as expected before deploying in Production environment.**

## Description {#description}

This page contains pre-release notes for the MDES Customer Service Application Programming Interface (CS API), providing early warning of intended changes and additions to the APIs. Only once the API update has been released to production will the specification be updated in the main API reference page. So the pre-release notes are the only place where coming changes are documented in advance of each MDES production release.
Note: The CS API content of any given release may change due to the agile nature of development. In such cases the relevant pre-release documentation will be updated accordingly. Every effort will be made to provide as much warning of change as possible, with a target of providing at least 3 months' notice.

If an MDES Platform release impacts MDES Customer Service API, the Pre-Release Notes document will be published for that release according to the MDES release calendar. Each document provides up-to-date details of the changes expected, and should be considered accurate at the point of publication.

If an MDES Platform release doesn't impact the MDES Customer Service API, the Pre-Release Notes will not be published for that release.

|                                                          Platform Release (for Customer Service API updates only)                                                          | Date of Upgrading |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------|
| [March 2026 - Customer Service API Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/release-notes-march2026/index.md)   | 9 March 2026      |
| [October 2025 - Customer Service API Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/release-notes-oct2025/index.md)   | 7 November 2025   |
| [June 2025 - Customer Service API Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/release-notes-june2025/index.md)     | 29 April 2025     |
| [January 2025 - Customer Service API Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/release-notes-jan2025/index.md)   | 16 December 2024  |
| [November 2024 - Customer Service API Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/release-notes-nov2024/index.md)  | 30 October 2024   |
| [September 2024 - Customer Service API Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/release-notes-sep2024/index.md) | 25 September 2024 |
| [June 2024 - Customer Service API Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/release-notes-june2024/index.md)     | 12 June 2024      |
| [April 2023 - Customer Service API Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/pre-release-april2023/index.md)     | 24 April 2023     |
| [February 2023 - Customer Service API Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/pre-release-feb2023/index.md)    | 08 March 2023     |
| [October 2022 - Customer Service API Pre-Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/pre-release-oct2022/index.md) | 11 November 2022  |
| [June 2022 - Customer Service API Pre-Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/pre-release-june2022/index.md)   | 27 June 2022      |
| [May 2022 - Customer Service API Pre-Release Notes](https://developer.mastercard.com/mdes-customer-service/documentation/release-history/pre-release-may2022/index.md)     | 26 April 2022     |

## Backward compatibility {#backward-compatibility}

Mastercard would like to clarify the 'backward compatibility' concept. Adding a new field in an API response is considered to be backward compatible, as we expect all our partners to code their solution to support additional fields.
However, the following cases are considered as 'backward breaking':

1. Adding a new value to an enumeration list, e.g. a new ReasonCode. The new value might disrupt issuers' implementations because we spelled out every valid value previously.
2. The conversion of NTU to an encrypted payload is another example (the fields that we sent completely changed).
3. Marking a required field as optional outbound calls (from MDES). Marking an optional field as required on an inbound request (to MDES).
4. Removing a required field (however: removing an optional field would be backward-compatible)
5. Adding a required field to an inbound call.

If there is a risk of 'backward breaking' the issuers' code, Mastercard automatically introduces a feature flag for issuers who are not yet ready to support the change. Flag enablement proceeds on a case-by-case basis depending on issuer preparedness.
Ultimately, the feature flag is removed once an announcement is made and Mastercard has the confirmation that all issuers can the support the new implementation. For more information, please contact your Mastercard representative.