• Bodies of POST requests are now escaped to ensure that valid Base64 always gets sent to the APIs. This allows custom proxy servers to expect valid Base64 in every case (the mixpanel.com API servers already accepted and handled the technically invalid Base64 chars).
• batch_requests will not default to true if a non-mixpanel.com api_host is specified, to avoid silently regressing existing setups with proxies that don't support batches. Batching can always be forced on by explicitly setting batch_requests: true.
• Default-on request-batching has been expanded to 30% of projects.