Known Limitations

• ETLantic 0.21.x is production/stable for documented single-tenant reference deployments, but 0.x releases may still introduce breaking API changes between minor versions until 1.0.
• Portable @Transformation.portable definitions and etlantic.transform/1 authoring are available since 0.11. 0.13 shipped Polars and PySpark compilers for portable-relational/1; 0.14 shipped the eager Pandas compiler; 0.15 shipped Safe SQL portable lowering for that baseline. 0.17 graduates Wave 1/2 families on Polars and PySpark: portable-string-advanced/1, portable-conversion/1, portable-statistics/1, portable-window/1, portable-complex-values/1, portable-complex-types/1, and portable-reshape/1. Pandas and SQL remain baseline-only (kernel + relational /1).
• Explicit window frames (rowsBetween / rangeBetween) fail closed in 0.17; first_value / last_value use ordered partition semantics until frames land. Continuation families (portable-window/2, temporal-iana, nondeterministic, relational-extended) remain unclaimed.
• Distinct missing / invalid three-state literals fail closed unless a compiler advertises semantic_mode:three_state_distinct (not claimed in 0.17). Polars does not claim dtcs:map (use dtcs:object); PySpark does.
• The planned PySpark-inspired syntax will intentionally support a closed subset; actions, arbitrary Python tracing, raw SQL expressions, and silent UDF fallback are excluded.
• Advanced DTCS 3.0 families are independently claimable profiles. Facades may emit IR for unclaimed families; first-party compilers reject them at analyze until claimed.
• Local execution is in-process; ETLantic is not a distributed scheduler.
• Spark batch execution is available via etlantic-pyspark (0.7+). Managed cloud providers (Databricks/EMR/Connect) are not.
• Airflow DAG compilation is available via etlantic-airflow (0.8+). Dagster compilers are not shipped. Optional Prefect 3.x local scheduling ships via etlantic-prefect (0.16+) as an ExecutionScheduler (not a DAG compiler).
• Structured Streaming APIs are experimental in 0.7+.
• SQL plugins do not treat untrusted raw SQL as safe; use the typed expression model and dialect identifier/parameter APIs.
• MERGE / upsert is not implemented in the SQL reference plugin; requiring sql_merge fails closed at planning. Do not rely on SQL merge until a later release advertises and implements it.
• SQLite via ETLANTIC_SQL_URL is demo-only; it is not the SQL conformance reference (PostgreSQL via etlantic-sql is).
• Cross-database joins and distributed transactions are not supported.
• Polars LazyFrames are collected only at plan-declared boundaries; durable JSON workspace materialization requires collection to records first.
• Durable workspace storage rejects native frames/LazyFrames (fail closed); there is no durable LazyFrame workspace format yet.
• Pandas does not support lazy execution; requiring lazy fails at planning.
• Arrow interchange requires an optional PyArrow install; without it, cross-engine transfers use a documented copy fallback.
• Not every Polars/Pandas dtype maps losslessly; ambiguous or unsupported mappings produce structured diagnostics.
• Cancellation and thread-safety capability flags are not fully enforced by the reference plugins.
• Many design pages still describe intended 1.0 behavior. Check the page status and Capabilities before copying code.
• Process-local report history is not a durable report database.
• In-memory storage is intended for local development and tests.
• Generated plans should be regenerated after incompatible schema changes rather than edited by hand.
• Docs on main may briefly lead a published tag; pin etlantic==0.21.0 (or the version you evaluated) in production installs.

Release-specific fixes and changes are recorded in the changelog.