rego_compile_error: rego.v1 import is not supported when bundling with OPA v1.9

[irsolipuram]

I'm experiencing an issue after upgrading from OPA v0.7 to OPA v1.9 and could use some guidance.
Setup:

• Upgraded OPA from v0.7 to v1.9
• Using OPA SDK Go integration
• Running producer with v0 compatibility. My go.mod has v1.9, but packages are all V0.
• Some policies contain import rego.v1 statements

Problem:
When attempting to bundle policies, I'm getting this error:
rego_compile_error: rego.v1 import is not supported

Questions:

• Why does import rego.v1 cause an error when using V0 packages in OPA v1.9?
• How come OPA v0.7 worked with rego.v1 imports but OPA v1.9 with V0 packages doesn't allow it?