Does the archive of a contract include a fetch of the full payload?

An archive is really the exercise of the implicit Archive choice present on every template, and a choice exercise requires fetching the contract, so at first glance the answer would be “yes”.

However, you only need to know the signatories to verify model conformance for archives, so in that case do we actually retain the full contract payload?

Any exercise includes an implicit fetch of the contract during interpretation. Archive isn’t treated any differently here.

However, the transaction format does not store payloads of exercised contracts in general (at least for non-divulged contracts). So there shouldn’t be significant storage overhead from the payload if the contract hasn’t been divulged.

cocreature:

However, the transaction format does not store payloads of exercised contracts in general (at least for non-divulged contracts). So there shouldn’t be significant storage overhead from the payload if the contract hasn’t been divulged.

I take it this is because one can verify model conformance for exercises whose actors are stakeholders by simply fetching the contract from the participant store?

Exactly