@@ -37,6 +37,11 @@
 from google.genai._gaos.types.interactions import functionresultstep
 from google.genai._gaos.types.interactions import modeloutputstep
 from google.genai._gaos.types.interactions import userinputstep
+
+try:
+    from google.genai._gaos.utils.serializers import ALLOW_UNKNOWN_UNION_VARIANTS
+except (ImportError, AttributeError):
+    ALLOW_UNKNOWN_UNION_VARIANTS = "speakeasy_allow_unknown_union_variants"
 from google.genai.models import Models
 import pandas as pd
 from tqdm import tqdm
@@ -775,7 +780,16 @@ def _interaction_dict_to_agent_data(
     Returns:
         An AgentData object with one or more ConversationTurns.
     """
-    typed_interaction = interaction_types.Interaction.model_validate(interaction)
+    # A server response, so unknown step types must degrade rather than raise.
+    # `Step` is an open discriminated union: parse_open_union only falls back to
+    # the Unknown variant when the validation context carries
+    # ALLOW_UNKNOWN_UNION_VARIANTS, and raises without it so that a
+    # user-constructed request payload surfaces its mistakes locally. This
+    # payload comes off the Interactions API, so it is on the tolerant side of
+    # that line. _interaction_steps_to_events already drops steps it cannot map.
+    typed_interaction = interaction_types.Interaction.model_validate(
+        interaction, context={ALLOW_UNKNOWN_UNION_VARIANTS: True}
+    )
     all_events = _interaction_steps_to_events(typed_interaction.steps or [])
 
     # Group events into turns. Each UserInputStep starts a new turn.
@@ -1689,8 +1703,12 @@ def _resolve_interactions_to_eval_cases(
                 break
             interaction_dict = json.loads(response.body)
             try:
+                # Also a server response -- see _interaction_dict_to_agent_data.
+                # Without the context a single step type this client does not
+                # know about raised, and the except below turned that into a
+                # `break`, silently truncating the interaction history.
                 typed_interaction = interaction_types.Interaction.model_validate(
-                    interaction_dict
+                    interaction_dict, context={ALLOW_UNKNOWN_UNION_VARIANTS: True}
                 )
             except Exception as e:
                 logger.warning("Failed to validate interaction model: %s", e)