diff --git a/dsl/gunbc/ci_failure_class.dag b/dsl/gunbc/ci_failure_class.dag
index 7dd2dda39a3..7ff780b3c04 100644
--- a/dsl/gunbc/ci_failure_class.dag
+++ b/dsl/gunbc/ci_failure_class.dag
@@ -11,6 +11,7 @@ type InfraSignature
   | ProcessSpawnFailure
   | SccacheFatalError
   | RunnerLost
+  | ClusteredOutOfMemoryKill
 
 type SignatureSite
   = BuildLog
@@ -33,6 +34,7 @@ fn infra_signature_match_substring(sig: InfraSignature) -> String {
     ProcessSpawnFailure => spawn_outcome_log_fragment(outcome: SpawnFailed)
     SccacheFatalError => sccache_fatal_error_log_fragment
     RunnerLost => runner_lifecycle_log_fragment(signal: ShutdownReceived)
+    ClusteredOutOfMemoryKill => "Out of memory: Killed process"
   }
 }
 
@@ -42,6 +44,7 @@ fn infra_signature_origin(sig: InfraSignature) -> String {
     ProcessSpawnFailure => "extdeps.rust.std_process (Command::spawn failure)"
     SccacheFatalError => "extdeps.cache.sccache (server fatal error)"
     RunnerLost => "extdeps.github.ci_runner (runner shutdown signal)"
+    ClusteredOutOfMemoryKill => "kernel cgroup memory.events oom_kill / systemd-oomd (cross-run clustered OOM, evidence-derived; not a log-grep roster signature)"
   }
 }
 
@@ -51,6 +54,7 @@ fn infra_signature_site(sig: InfraSignature) -> SignatureSite {
     ProcessSpawnFailure => BuildLog
     SccacheFatalError => BuildLog
     RunnerLost => JobSignal
+    ClusteredOutOfMemoryKill => JobSignal
   }
 }
 
diff --git a/dsl/gunbc/ci_oom_reclassify.dag b/dsl/gunbc/ci_oom_reclassify.dag
new file mode 100644
index 00000000000..e86706d1a5f
--- /dev/null
+++ b/dsl/gunbc/ci_oom_reclassify.dag
@@ -0,0 +1,91 @@
+module gunbc.ci_oom_reclassify
+
+import gunbc.ci_failure_class {
+  FloorOutcome, NoFailure, FloorFailed,
+  FloorFailureClass, Infra, Structural,
+  InfraSignature, ClusteredOutOfMemoryKill
+}
+
+type OomKillSource
+  = CgroupMemoryEvents
+  | SystemdOomdJournal
+
+type OomKillObservation
+  = OomKillConfirmed { source: OomKillSource }
+  | NoOomKillObserved
+
+type ClusteringSignal
+  = SimultaneousMultiJobDeath { job_count: Int }
+  | HostBootIdReset
+
+type ClusteringEvidence
+  = Clustered { signal: ClusteringSignal }
+  | NotClustered
+
+fn oom_kill_from_cgroup_counter(oom_kill_count: Int) -> OomKillObservation {
+  if oom_kill_count > 0 {
+    OomKillConfirmed { source: CgroupMemoryEvents }
+  } else {
+    NoOomKillObserved
+  }
+}
+
+fn oom_kill_from_oomd_journal(oomd_kill_record_count: Int) -> OomKillObservation {
+  if oomd_kill_record_count > 0 {
+    OomKillConfirmed { source: SystemdOomdJournal }
+  } else {
+    NoOomKillObserved
+  }
+}
+
+fn observe_oom_kill(cgroup: OomKillObservation, oomd: OomKillObservation) -> OomKillObservation {
+  match cgroup {
+    OomKillConfirmed { source: _ } => cgroup
+    NoOomKillObserved => oomd
+  }
+}
+
+fn oom_is_confirmed(o: OomKillObservation) -> Bool {
+  match o {
+    OomKillConfirmed { source: _ } => true
+    NoOomKillObserved => false
+  }
+}
+
+fn host_boot_id_reset(boot_id_before: String, boot_id_after: String) -> Bool {
+  boot_id_before != boot_id_after
+}
+
+fn clustering_signal_from_boot_id(boot_id_before: String, boot_id_after: String) -> ClusteringEvidence {
+  if host_boot_id_reset(boot_id_before: boot_id_before, boot_id_after: boot_id_after) {
+    Clustered { signal: HostBootIdReset }
+  } else {
+    NotClustered
+  }
+}
+
+fn clustering_is_present(c: ClusteringEvidence) -> Bool {
+  match c {
+    Clustered { signal: _ } => true
+    NotClustered => false
+  }
+}
+
+fn reclassify_floor_failure(c: FloorFailureClass, oom: OomKillObservation, clustering: ClusteringEvidence) -> FloorFailureClass {
+  match c {
+    Infra { signature: _ } => c
+    Structural { reason: _ } =>
+      if oom_is_confirmed(o: oom) && clustering_is_present(c: clustering) {
+        Infra { signature: ClusteredOutOfMemoryKill }
+      } else {
+        c
+      }
+  }
+}
+
+fn reclassify_floor_outcome(o: FloorOutcome, oom: OomKillObservation, clustering: ClusteringEvidence) -> FloorOutcome {
+  match o {
+    NoFailure => o
+    FloorFailed { class: c } => FloorFailed { class: reclassify_floor_failure(c: c, oom: oom, clustering: clustering) }
+  }
+}
diff --git a/dsl/test/claim/ci_oom_reclassify_witness_test.dag b/dsl/test/claim/ci_oom_reclassify_witness_test.dag
new file mode 100644
index 00000000000..ef957eb985c
--- /dev/null
+++ b/dsl/test/claim/ci_oom_reclassify_witness_test.dag
@@ -0,0 +1,125 @@
+module test.claim.ci_oom_reclassify_witness
+
+import std.process { ProcessExit, ExitFailure }
+import gunbc.ci_failure_class {
+  FloorOutcome, NoFailure, FloorFailed,
+  FloorFailureClass, Infra, Structural,
+  ClusteredOutOfMemoryKill,
+  classify_floor_exit, floor_outcome_blocks_merge
+}
+import gunbc.ci_oom_reclassify {
+  OomKillSource, CgroupMemoryEvents, SystemdOomdJournal,
+  OomKillObservation, OomKillConfirmed, NoOomKillObserved,
+  ClusteringSignal, SimultaneousMultiJobDeath, HostBootIdReset,
+  ClusteringEvidence, Clustered, NotClustered,
+  oom_kill_from_cgroup_counter, oom_kill_from_oomd_journal,
+  observe_oom_kill, oom_is_confirmed,
+  host_boot_id_reset, clustering_signal_from_boot_id, clustering_is_present,
+  reclassify_floor_failure, reclassify_floor_outcome
+}
+
+fn bare_137_outcome() -> FloorOutcome {
+  classify_floor_exit(e: ExitFailure { code: 137, reason: "Process completed with exit code 137." })
+}
+
+fn outcome_is_infra(o: FloorOutcome) -> Bool {
+  match o {
+    NoFailure => false
+    FloorFailed { class: c } => match c {
+      Infra { signature: _ } => true
+      Structural { reason: _ } => false
+    }
+  }
+}
+
+fn outcome_is_structural(o: FloorOutcome) -> Bool {
+  match o {
+    NoFailure => false
+    FloorFailed { class: c } => match c {
+      Infra { signature: _ } => false
+      Structural { reason: _ } => true
+    }
+  }
+}
+
+fn confirmed_cgroup_oom() -> OomKillObservation {
+  observe_oom_kill(cgroup: oom_kill_from_cgroup_counter(oom_kill_count: 1), oomd: oom_kill_from_oomd_journal(oomd_kill_record_count: 0))
+}
+
+fn confirmed_oomd_oom() -> OomKillObservation {
+  observe_oom_kill(cgroup: oom_kill_from_cgroup_counter(oom_kill_count: 0), oomd: oom_kill_from_oomd_journal(oomd_kill_record_count: 1))
+}
+
+fn no_oom() -> OomKillObservation {
+  observe_oom_kill(cgroup: oom_kill_from_cgroup_counter(oom_kill_count: 0), oomd: oom_kill_from_oomd_journal(oomd_kill_record_count: 0))
+}
+
+fn clustered_simultaneous() -> ClusteringEvidence {
+  Clustered { signal: SimultaneousMultiJobDeath { job_count: 3 } }
+}
+
+fn witness_clustered_oom_promotes_137_to_infra_nonblocking() -> Bool {
+  let before = bare_137_outcome()
+  let after = reclassify_floor_outcome(o: before, oom: confirmed_cgroup_oom(), clustering: clustered_simultaneous())
+  outcome_is_structural(o: before)
+    && floor_outcome_blocks_merge(o: before)
+    && outcome_is_infra(o: after)
+    && (floor_outcome_blocks_merge(o: after) == false)
+}
+
+fn witness_boot_id_reset_clustering_also_promotes() -> Bool {
+  let before = bare_137_outcome()
+  let clu = clustering_signal_from_boot_id(boot_id_before: "boot-uuid-A", boot_id_after: "boot-uuid-B")
+  let after = reclassify_floor_outcome(o: before, oom: confirmed_oomd_oom(), clustering: clu)
+  clustering_is_present(c: clu)
+    && outcome_is_infra(o: after)
+    && (floor_outcome_blocks_merge(o: after) == false)
+}
+
+fn witness_lone_137_no_clustering_stays_structural_blocks() -> Bool {
+  let before = bare_137_outcome()
+  let after = reclassify_floor_outcome(o: before, oom: confirmed_cgroup_oom(), clustering: NotClustered)
+  outcome_is_structural(o: after)
+    && floor_outcome_blocks_merge(o: after)
+}
+
+fn witness_no_confirmed_oom_stays_structural_blocks() -> Bool {
+  let before = bare_137_outcome()
+  let after = reclassify_floor_outcome(o: before, oom: no_oom(), clustering: clustered_simultaneous())
+  (oom_is_confirmed(o: no_oom()) == false)
+    && outcome_is_structural(o: after)
+    && floor_outcome_blocks_merge(o: after)
+}
+
+fn witness_dispatch_two_handlers_one_fact() -> Bool {
+  oom_is_confirmed(o: confirmed_cgroup_oom())
+    && oom_is_confirmed(o: confirmed_oomd_oom())
+    && (oom_is_confirmed(o: no_oom()) == false)
+}
+
+fn witness_boot_id_oracle_discriminates() -> Bool {
+  host_boot_id_reset(boot_id_before: "boot-uuid-A", boot_id_after: "boot-uuid-B")
+    && (host_boot_id_reset(boot_id_before: "boot-uuid-A", boot_id_after: "boot-uuid-A") == false)
+}
+
+fn witness_reclassify_never_demotes_or_touches_non_137() -> Bool {
+  let no_failure = reclassify_floor_outcome(o: NoFailure, oom: confirmed_cgroup_oom(), clustering: clustered_simultaneous())
+  let already_infra = FloorFailed { class: Infra { signature: ClusteredOutOfMemoryKill } }
+  let still_infra = reclassify_floor_outcome(o: already_infra, oom: no_oom(), clustering: NotClustered)
+  let real_compile_error = FloorFailed { class: Structural { reason: "error[E0599]: no method named frobnicate" } }
+  let unchanged = reclassify_floor_outcome(o: real_compile_error, oom: no_oom(), clustering: clustered_simultaneous())
+  (match no_failure { NoFailure => true  FloorFailed { class: _ } => false })
+    && outcome_is_infra(o: still_infra)
+    && outcome_is_structural(o: unchanged)
+    && floor_outcome_blocks_merge(o: unchanged)
+}
+
+test fn ci_oom_reclassify_witnesses() -> Bool {
+  witness_clustered_oom_promotes_137_to_infra_nonblocking()
+    && witness_boot_id_reset_clustering_also_promotes()
+    && witness_lone_137_no_clustering_stays_structural_blocks()
+    && witness_no_confirmed_oom_stays_structural_blocks()
+    && witness_dispatch_two_handlers_one_fact()
+    && witness_boot_id_oracle_discriminates()
+    && witness_reclassify_never_demotes_or_touches_non_137()
+}