The specification repository carries five dated revisions plus a working draft: 2024-11-05, 2025-03-26, 2025-06-18, 2025-11-25, 2026-07-28. That is five revisions in roughly twenty-one months — a new one about every five months, and the current one is weeks old at the time of writing.
What that should change about how you build: the protocol version is not a thing you set once. Pin it explicitly, know which one you implement, and expect to revisit it about twice a year. A server that silently claims the newest version because its library was updated is a server whose behaviour changed without a decision being made.
It also means documentation ages fast in this area, including the search results you will find first. Anything written more than two revisions ago describes a protocol that has since moved, and it usually will not say which revision it was written against — checking the date on MCP material is not pedantry here, it is the difference between current and wrong.