diff --git a/book/source/02-highlevel.md b/book/source/02-highlevel.md
index 7b14735..2ba79c4 100644
--- a/book/source/02-highlevel.md
+++ b/book/source/02-highlevel.md
@@ -76,9 +76,8 @@ OpenPGP was standardized in 1997 to encourage development of interoperable imple
 Historically, interoperability has only been tested in an adhoc manner. Since 2019, the Sequoia project is maintaining and operating the ["OpenPGP interoperability test suite"](https://tests.sequoia-pgp.org/), for more rigorous and systematic testing. The test suite has identified numerous [issues](https://gitlab.com/sequoia-pgp/openpgp-interoperability-test-suite#hall-of-fame).
 
 ## The road ahead
-```{admonition} TODO
-Let's insert a line about v5.
-```
+> **Note:** Software and protocol development sometimes skip version numbers due to reasons like internal testing, significant changes, avoiding confusion, marketing decisions, or technical issues. The official successor to OpenPGP version 4 is OpenPGP version 6, detailed below.
+
 ### OpenPGP version 6
 
 As of this writing (in 2023), [version 6 of OpenPGP](https://datatracker.ietf.org/doc/draft-ietf-openpgp-crypto-refresh/) is approaching publication as an RFC.