Version 4.0 of the electronic Common Technical Document (eCTD) is the upcoming next major version of the electronic submission format.

CDER and CBER plan to accept new applications in eCTD v4.0 format in 2023.

The current version, v3.2.2, which is used by most global health authorities, including US FDA, EMA, Canada, Japan, and many others. Health authorities like EMA, Swissmedic, US FDA, EMA, Japan’s MHLW have published implementation guidelines regarding eCTD v4.0.

The core objective of the new eCTD version 4.0 standard is to better facilitate the processing and review of electronic submissions between sponsor and regulators, as well as promoting better re-use of content. It does this by introducing:

• Single Submission Unit Message: The eCTD v4.0 message, submissionunit.xml and submission content, contains all information necessary to submit a complete sequence to the FDA. The submissionunit.xml is used to organize both the ICH and Regional sequence content, including the study data that was previously submitted in a separate Study Tagging xml file.
• Context of Use: Context of Use specifies where documents are to be inserted into the CTD/eCTD TOC when presenting a reviewable structure.
• Document re-use: eCTD v4.0 will allow for document re-use, where each document will be assigned with a unique ID that can be referenced as long as it’s in an Agency’s system.
• Two-way communication: eCTD v4.0 defines a bi-directional communication, which enables agencies to send correspondence to a sponsor, such as a request for information, as an eCTD sequence.
• A new XML schema: Designed to improve robustness, flexibility, and long-term stability of the messaging system.

For more detail refer https://www.fda.gov/media/135573/download