How do you handle API versioning for internal and external consumers?

So, we're building some new services, and API versioning is always a hot topic. For our public APIs, using semantic versioning and having clear deprecation rules just makes sense. But what about our internal services, the ones that talk to each other? Should we be just as strict with versioning there, or can we be a bit more flexible? I'm worried about all the extra work managing a bunch of internal versions, but I also don't want to cause huge problems with breaking changes if we're too loose. Anyone have thoughts or go-to strategies for internal API versioning, especially when you're working with microservices?