I have a valid schema document that contains the following $schema value:

{
  "$schema": "http://json-schema.org/draft-07/schema/#"
}

When validating an instance against this schema, I get the following warning:

/usr/local/lib/python3.7/site-packages/jsonschema/validators.py:893: DeprecationWarning: The metaschema specified by $schema was not found. Using the latest draft to validate, but this will raise an error in the future.

I discovered that I can suppress the error by changing removing the trailing slash and hash from the schema URI, e.g. http://json-schema.org/draft-07/schema.

I think the validator should allow for some variations on URI formats--the JSON Schema documentation specifies the $schema value with the trailing slash and hash, so I believe that will be the most common format users attempt.