Right now, we have some inconsistent behavior in terms of using aliases in validation and serialization.

By default, if an alias or validation_alias is defined on a field, we use the alias for validation. This behavior can be changed by setting populate_by_name to True on the model_config.

Conversely, if an alias or serialization_alias is defined on a field, that alias not used by default for serialization. We must specify by_alias=True in the call to model_dump + other serialization functions.

I propose that in V3:

• We use alias by default for both validation and serialization
• We add a field (or fields, but ideally just one) to ConfigDict to support different behavior than the default

This is a breaking change, hence the V3 label.

Requests to change the inconsistent default behavior have been made for a few years, so I'm going to comb through issues and close those so we can centralize discussion here.