I understand from official Docs Anthos is built on Kubernetes/Istio/Knative but where does Anthos fits in Google cloud platform.
Can it act as configuration manager for application auto-deployment, provisioning etc ?
Does it provide support for language specific build on the fly?
With Anthos you can basically manage multiple Kubernetes clusters from multiple Clouds (Amazon, Google, Azure) and on-prem. It can help you maintain a hybrid environment and move in a predictable way or partially your infrastructure from on-prem to cloud.
You can use Anthos Config Management to create a common configuration for your clusters. You can use ClusterSelectors to apply configurations to subsets of clusters. Configuration can include Istio service mesh, pod security policies, or quota policies.
From a security perspective, you can manage your policies using Anthos Policy Controller, enforcing PodSecurityPolicies, with the advantage of testing constraints before enforcing them.