For streaming (using AWS Kinesis Stream) from AWS GuardDuty to Splunk, check out this blog post: https://www.splunk.com/blog/2018/02/22/serving-it-up-with-aws-and-splunk-aws-serverless-application-repository-now-available.html
To send GuardDuty CloudWatch events to Splunk over HTTP Event Collector, using the Splunk Logging AWS Lambda Blueprint, check out this video: https://www.youtube.com/watch?v=wlPfzUZMS6E
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