The camel-jetty page has a "httpClient" option that can be set on camel-jetty producer endpoint and it says:

To use a shared org.eclipse.jetty.client.HttpClient for all producers created by this endpoint. This option should only be used in special circumstances.

In some cases, user might want to set a shard Jetty HttpClient among camel-jetty producer endpoints. For instance, user might use recipientList with camel-jetty producer endpoint to support multiple dynamically created URLs. So setting a shared Jetty HttpClient with a shared thread pool would be ideal to avoid exploding number of producer endpoints + their own producer thread pools in this use case. However, there is no way to set it to camel-jetty producer endpoint.

For more details, please take a look at upstream JIRA:
https://issues.apache.org/jira/browse/CAMEL-9713