This comes from a Slack discussion where a user was asking about how to set this field: https://coreos.slack.com/archives/CLMP7R2G2/p1664178292639599

Per comment from Stavros:

 
new fields were added/exposed in Knative 1.7+ (https://github.com/knative/serving/pull/12970). Fields in RevisionSpec can be set at the ksvc level using the path spec.template.spec(https://github.com/nader-ziada/serving/blob/8c0f7bd754563d9839dc4403042fbe89b3536381/pkg/testing/v1/service.go#L186)
kind: Service
metadata:
name: helloworld-go
spec:
template:
metadata:
labels:
app: helloworld-go
spec:
responseStartTimeoutSeconds: 10
...