fix(grouping): Preserve fingerprint component boundaries in beta config

src/sentry/conf/server.py

@@ -3193,10 +3193,11 @@ def custom_parameter_sort(parameter: dict) -> tuple[str, int]:
 
 WINTER_2023_GROUPING_CONFIG = "newstyle:2023-01-11"
 FALL_2025_GROUPING_CONFIG = "newstyle:2026-01-20"
+FALL_2026_GROUPING_CONFIG = "newstyle:2026-10-24"
 # Note: When the default config here is updated, `DEFAULT_ENHANCEMENTS_BASE` in
 # `sentry.grouping.enhancer.__init__` *may* also need to be updated.
 DEFAULT_GROUPING_CONFIG = FALL_2025_GROUPING_CONFIG
-BETA_GROUPING_CONFIG = ""
+BETA_GROUPING_CONFIG = FALL_2026_GROUPING_CONFIG
 
 # How long the migration phase for grouping lasts
 SENTRY_GROUPING_CONFIG_TRANSITION_DURATION = 90 * 24 * 3600  # 90 days, until groups age out

src/sentry/grouping/api.py

@@ -433,7 +433,9 @@ def get_grouping_variants_for_event(
         )
         hint = f"ignored because {fingerprint_source} fingerprint takes precedence"
 
-        fingerprint_variant = CustomFingerprintVariant(resolved_fingerprint, fingerprint_info)
+        fingerprint_variant = CustomFingerprintVariant(
+            resolved_fingerprint, fingerprint_info, context.config
+        )
         additional_variants[fingerprint_variant.key] = fingerprint_variant
 
         for variant in strategy_component_variants.values():

src/sentry/grouping/ingest/config.py

@@ -26,6 +26,7 @@
 # Used to migrate projects that have no activity via getsentry scripts
 CONFIGS_TO_DEPRECATE = set(GROUPING_CONFIG_CLASSES.keys()) - {
     DEFAULT_GROUPING_CONFIG,
+    BETA_GROUPING_CONFIG,
 }
 
 

src/sentry/grouping/strategies/configurations.py

@@ -1,4 +1,8 @@
-from sentry.conf.server import FALL_2025_GROUPING_CONFIG, WINTER_2023_GROUPING_CONFIG
+from sentry.conf.server import (
+    FALL_2025_GROUPING_CONFIG,
+    FALL_2026_GROUPING_CONFIG,
+    WINTER_2023_GROUPING_CONFIG,
+)
 from sentry.grouping.strategies.base import (
     StrategyConfiguration,
     create_strategy_configuration_class,
@@ -82,3 +86,10 @@ def register_grouping_config(id: str, **kwargs) -> type[StrategyConfiguration]:
     },
     enhancements_base="all-platforms:2026-01-20",
 )
+
+# Opt-in only: changing fingerprint encoding changes existing custom and hybrid hashes.
+register_grouping_config(
+    id=FALL_2026_GROUPING_CONFIG,
+    base=FALL_2025_GROUPING_CONFIG,
+    initial_context={"fingerprint_value_boundaries": True},
+)

src/sentry/grouping/utils.py

@@ -17,15 +17,24 @@
     from sentry.services.eventstore.models import BaseEvent
 
 
-def hash_from_values(values: Iterable[str | int | UUID | ExceptionGroupingComponent]) -> str:
+def hash_from_values(
+    values: Iterable[str | int | UUID | ExceptionGroupingComponent],
+    *,
+    with_value_boundaries: bool = False,
+) -> str:
     """
     Primarily used at the end of the grouping process, to get a final hash value once the all of the
     variants have been constructed, but also used as a hack to compare exception components (by
     stringifying their reprs) when calculating variants for chained exceptions.
     """
     result = md5()
     for value in values:
-        result.update(force_bytes(value, errors="replace"))
+        value_bytes = force_bytes(value, errors="replace")
+        if with_value_boundaries:
+            # Length-prefix the encoded bytes so empty values and values containing delimiters
+            # cannot obscure fingerprint boundaries. Keep legacy callers unchanged by default.
+            result.update(f"{len(value_bytes)}:".encode("ascii"))
+        result.update(value_bytes)
     return result.hexdigest()
 
 

src/sentry/grouping/variants.py

@@ -193,7 +193,13 @@ class CustomFingerprintVariant(BaseVariant):
 
     type = "custom_fingerprint"
 
-    def __init__(self, fingerprint: list[str], fingerprint_info: FingerprintInfo):
+    def __init__(
+        self,
+        fingerprint: list[str],
+        fingerprint_info: FingerprintInfo,
+        strategy_config: StrategyConfiguration,
+    ):
+        self.config = strategy_config
         self.values = fingerprint
         self.fingerprint_info = fingerprint_info
         self.is_built_in = fingerprint_info.get("matched_rule", {}).get("is_builtin", False)
@@ -207,7 +213,12 @@ def key(self) -> str:
         return get_custom_fingerprint_description(self.fingerprint_info)
 
     def get_hash(self) -> str | None:
-        return hash_from_values(self.values)
+        return hash_from_values(
+            self.values,
+            with_value_boundaries=self.config.initial_context.get(
+                "fingerprint_value_boundaries", False
+            ),
+        )
 
     def _get_metadata_as_dict(self) -> FingerprintVariantMetadata:
         return expose_fingerprint_dict(self.values, self.fingerprint_info)
@@ -260,15 +271,24 @@ def description(self) -> str:
     def get_hash(self) -> str | None:
         if not self.root_component.contributes:
             return None
+        with_value_boundaries = self.config.initial_context.get(
+            "fingerprint_value_boundaries", False
+        )
         final_values: list[str | int] = []
         for value in self.values:
             # If we've hit the `{{ default }}` part of the fingerprint, pull in values from the
             # original grouping method (message, stacktrace, etc.)
             if is_default_fingerprint_var(value):
-                final_values.extend(self.root_component.iter_values())
+                if with_value_boundaries:
+                    # Treat the entire default grouping contribution as one fingerprint value.
+                    # Preserve its existing equivalence rules rather than introducing boundaries
+                    # between internal stacktrace or exception components.
+                    final_values.append("".join(str(v) for v in self.root_component.iter_values()))
+                else:
+                    final_values.extend(self.root_component.iter_values())
             else:
                 final_values.append(value)
-        return hash_from_values(final_values)
+        return hash_from_values(final_values, with_value_boundaries=with_value_boundaries)
 
     def _get_metadata_as_dict(self) -> Mapping[str, Any]:
         return {