Upgrade Agent or Proxy

[!IMPORTANT]
Documentation Update: Product documentation, which were located in this repository under /website, are now located in hashicorp/web-unified-docs, colocated with all other product documentation. Contributions to this content should be done in the web-unified-docs repo, and not this one. Changes made to /website content in this repo will not be reflected on the developer.hashicorp.com website.

The Vault Agent is an API client of the Vault Server. Vault APIs are almost always backwards compatible. When they are not, this is called out in the upgrade guide for the new Vault version, and there is a lengthy deprecation period. The Vault Agent version can lag behind the Vault Server version, though we recommend keeping all Vault instances up to date with the most recent minor Vault version to the extent possible.