dbt source snapshot-freshness has been renamed to dbt source freshness. Its node selection logic is now consistent with other tasks. In order to check freshness for a specific source, you must prefix it with source:.
Snowflake: Turn off transactions and turn on autocommit by default. Explicitly specify begin and commit for DML statements in incremental and snapshot materializations. Note that this may affect user-space code that depends on transactions.
manifest.json uses a v3 schema that includes additional node properties (no changes to existing properties)
run_results.json uses a v3 schema that has added skipped as a potential TestResult
sources.json has a new v2 schema that has added timing and thread details
Test selection examples includes more discussion of indirect selection (a change in v0.20), and the optional "greedy" flag/property (new in v0.21), which you can optionally set to include tests that have a mix of selected + unselected parents