diff --git a/harnesses/axelar-gmp-latency/cmd/script/chains.go b/harnesses/axelar-gmp-latency/cmd/script/chains.go
index 2c83c54f..2b62f176 100644
--- a/harnesses/axelar-gmp-latency/cmd/script/chains.go
+++ b/harnesses/axelar-gmp-latency/cmd/script/chains.go
@@ -14,6 +14,27 @@ import "strings"
 //   - Cosmos chains (osmosis, injective, sei, celestia, kava) are
 //     Axelar-exclusive coverage vs Wormhole/LayerZero/CCIP/Hyperlane
 //
+// axelarTrackedChains is the set of OCB canonical slugs we record metrics for.
+// Only messages where BOTH source AND destination are in this set are
+// observed, capping cardinality at len²×buckets.
+// Derived from the bench YAML provider slugs.
+var axelarTrackedChains = map[string]bool{
+	"ethereum":  true,
+	"polygon":   true,
+	"base":      true,
+	"moonbeam":  true,
+	"osmosis":   true,
+	"arbitrum":  true,
+	"avalanche": true,
+	"bnb":       true,
+	"celo":      true,
+	"injective": true,
+	"linea":     true,
+	"mantle":    true,
+	"optimism":  true,
+	"scroll":    true,
+}
+
 // Unknown names fall through to `chain-<lowered>` so we never drop data.
 var axelarChainSlug = map[string]string{
 	// EVM L1s
diff --git a/harnesses/axelar-gmp-latency/cmd/script/main.go b/harnesses/axelar-gmp-latency/cmd/script/main.go
index a3652e99..55ff6b41 100644
--- a/harnesses/axelar-gmp-latency/cmd/script/main.go
+++ b/harnesses/axelar-gmp-latency/cmd/script/main.go
@@ -173,8 +173,10 @@ func poll(ctx context.Context, client *http.Client, seen *lruSet) error {
 		totalMs := float64(m.TimeSpent.Total) * 1000
 		if totalMs > 0 && totalMs <= maxLatencyMs {
 			dst := canonicalizeAxelarChain(m.Call.ReturnValues.DestinationChain)
-			axelarE2ELatencyMs.WithLabelValues(src, dst).Observe(totalMs)
-			axelarSeenTotal.WithLabelValues(src, dst).Inc()
+			if axelarTrackedChains[src] && axelarTrackedChains[dst] {
+				axelarE2ELatencyMs.WithLabelValues(src, dst).Observe(totalMs)
+				axelarSeenTotal.WithLabelValues(src, dst).Inc()
+			}
 		}
 
 		seen.add(m.ID)
diff --git a/harnesses/chainlink-ccip-latency/cmd/script/chains.go b/harnesses/chainlink-ccip-latency/cmd/script/chains.go
index e551d3c4..bb3a17fe 100644
--- a/harnesses/chainlink-ccip-latency/cmd/script/chains.go
+++ b/harnesses/chainlink-ccip-latency/cmd/script/chains.go
@@ -12,6 +12,32 @@ package main
 // makes the mapping legible and the audit trail obvious when CCIP
 // adds a new chain we didn't anticipate.
 //
+// ccipTrackedChains is the set of OCB canonical slugs we record metrics for.
+// Only messages where BOTH source AND destination are in this set are
+// observed, capping cardinality at len²×buckets.
+// Derived from the bench YAML provider slugs.
+var ccipTrackedChains = map[string]bool{
+	"ethereum":   true,
+	"bnb":        true,
+	"polygon":    true,
+	"avalanche":  true,
+	"arbitrum":   true,
+	"base":       true,
+	"robinhood":  true,
+	"berachain":  true,
+	"celo":       true,
+	"ink":        true,
+	"linea":      true,
+	"mantle":     true,
+	"monad":      true,
+	"moonbeam":   true,
+	"optimism":   true,
+	"scroll":     true,
+	"solana":     true,
+	"unichain":   true,
+	"world-chain": true,
+}
+
 // Only mainnet entries are mapped; testnet rows are dropped in main.go
 // via the `environment != "mainnet"` guard so we never emit test-chain
 // latency.
diff --git a/harnesses/chainlink-ccip-latency/cmd/script/main.go b/harnesses/chainlink-ccip-latency/cmd/script/main.go
index 19b6e3c8..c4a0cece 100644
--- a/harnesses/chainlink-ccip-latency/cmd/script/main.go
+++ b/harnesses/chainlink-ccip-latency/cmd/script/main.go
@@ -189,6 +189,10 @@ func poll(ctx context.Context, client *http.Client, seen *lruSet) error {
 			seen.add(m.MessageID)
 			continue
 		}
+		if !ccipTrackedChains[srcSlug] || !ccipTrackedChains[dstSlug] {
+			seen.add(m.MessageID)
+			continue
+		}
 		ccipLatencyMs.WithLabelValues(srcSlug, dstSlug).Observe(deltaMs)
 		ccipSeenTotal.WithLabelValues(srcSlug, dstSlug).Inc()
 		seen.add(m.MessageID)
diff --git a/harnesses/layerzero-message-latency/cmd/script/chains.go b/harnesses/layerzero-message-latency/cmd/script/chains.go
index 2c888741..ded44292 100644
--- a/harnesses/layerzero-message-latency/cmd/script/chains.go
+++ b/harnesses/layerzero-message-latency/cmd/script/chains.go
@@ -10,6 +10,35 @@ package main
 //   - LayerZero exposes a bunch of exotic chains (orderly, flare, ape,
 //     robinhood, hyperliquid) that map to our slugs where they exist.
 //
+// lzTrackedChains is the set of OCB canonical slugs we record metrics for.
+// Only messages where BOTH source AND destination are in this set are
+// observed. This caps cardinality at len²×buckets instead of the full
+// N×N cross-product of all chains LayerZero supports.
+// Derived from the bench YAML provider slugs — add here when adding a
+// new chain to the bench.
+var lzTrackedChains = map[string]bool{
+	"ethereum":  true,
+	"solana":    true,
+	"bnb":       true,
+	"arbitrum":  true,
+	"base":      true,
+	"optimism":  true,
+	"polygon":   true,
+	"avalanche": true,
+	"robinhood": true,
+	"monad":     true,
+	"berachain": true,
+	"celo":      true,
+	"injective": true,
+	"ink":       true,
+	"linea":     true,
+	"mantle":    true,
+	"moonbeam":  true,
+	"scroll":    true,
+	"sui":       true,
+	"unichain":  true,
+}
+
 // Unknown names fall through to a synthetic `chain-<lowered>` slug in
 // main.go so we never drop data silently.
 var lzChainSlug = map[string]string{
diff --git a/harnesses/layerzero-message-latency/cmd/script/main.go b/harnesses/layerzero-message-latency/cmd/script/main.go
index 5f7a4f6d..3ccfc0d0 100644
--- a/harnesses/layerzero-message-latency/cmd/script/main.go
+++ b/harnesses/layerzero-message-latency/cmd/script/main.go
@@ -206,6 +206,10 @@ func poll(ctx context.Context, client *http.Client, seen *lruSet) error {
 				continue
 			}
 			dstSlug := chainSlug(m.Pathway.Receiver.Chain)
+			if !lzTrackedChains[srcSlug] || !lzTrackedChains[dstSlug] {
+				seen.add(m.GUID)
+				continue
+			}
 			lzLatencyMs.WithLabelValues(srcSlug, dstSlug).Observe(deltaMs)
 			lzSeenTotal.WithLabelValues(srcSlug, dstSlug).Inc()
 			seen.add(m.GUID)