EZproxy 6.6.2 and later
Based on the suggestion of RFC7230 that an HTTP server should support request lines up to 8000 characters, EZproxy now allows URLs to be 8000 characters long. URLs of this length should always work during the proxying process. If a target URL of this length is presented in a starting point URL, though, the URL may end up being truncated if it must be transformed through the login process in ways that encode it to a longer length.
The actual size is 1024 * 8, or 8192 bytes, including its null terminator, making the actual limit 8191 bytes.