> ## Documentation Index
> Fetch the complete documentation index at: https://startai.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Versioning

The Model Context Protocol uses string-based version identifiers following the format
`YYYY-MM-DD`, to indicate the last date backwards incompatible changes were made.

<Info>The protocol version will *not* be incremented when the
protocol is updated, as long as the changes maintain backwards compatibility. This allows
for incremental improvements while preserving interoperability.</Info>

## Revisions

Revisions may be marked as:

* **Draft**: in-progress specifications, not yet ready for consumption.
* **Current**: the current protocol version, which is ready for use and may continue to
  receive backwards compatible changes.
* **Final**: past, complete specifications that will not be changed.

The **current** protocol version is [**2025-03-26**](/specification/2025-03-26/).

## Negotiation

Version negotiation happens during
[initialization](/specification/2025-03-26/basic/lifecycle#initialization). Clients and
servers **MAY** support multiple protocol versions simultaneously, but they **MUST**
agree on a single version to use for the session.

The protocol provides appropriate error handling if version negotiation fails, allowing
clients to gracefully terminate connections when they cannot find a version compatible
with the server.