diff --git a/example-cl-mimicry.yaml b/example-cl-mimicry.yaml
index d852800a9..385bdd51a 100644
--- a/example-cl-mimicry.yaml
+++ b/example-cl-mimicry.yaml
@@ -116,6 +116,34 @@ outputs:
 #   # Configuration for events without sharding keys (Group D events)
 #   noShardingKeyEvents:
 #     enabled: true # Process all events without sharding keys
+#
+# randomSampling:
+#   # Random sampling configuration - provides a "second chance" for events
+#   # that were NOT captured by deterministic sharding.
+#   #
+#   # Pattern Format:
+#   # - For GroupC events (IWANT, IDONTWANT - no topic): Use exact event type
+#   #   e.g., "LIBP2P_TRACE_RPC_META_CONTROL_IWANT"
+#   # - For GroupA/B events (with topic): Use "EVENT_TYPE*:topic_pattern"
+#   #   e.g., "LIBP2P_TRACE_RPC_META_CONTROL_IHAVE*:.*attestation.*"
+#   # - For topic-only patterns: Use regex pattern
+#   #   e.g., ".*beacon_block.*"
+#   #
+#   # Note: Random sampling only applies to events REJECTED by deterministic
+#   # sharding. Events already accepted are NOT sampled again (no duplicates).
+#   patterns:
+#     # 2% random sample of IWANT events
+#     "LIBP2P_TRACE_RPC_META_CONTROL_IWANT":
+#       chance: "2%"
+#
+#     # 2% random sample of IHAVE attestation events
+#     "LIBP2P_TRACE_RPC_META_CONTROL_IHAVE*:.*attestation.*":
+#       chance: "2%"
+#
+#     # 0.5% catch-all for any other rejected events
+#     ".*":
+#       chance: "0.5%"
+#
 # events:
 #   recvRpcEnabled: false
 #   sendRpcEnabled: false
diff --git a/pkg/clmimicry/config.go b/pkg/clmimicry/config.go
index 0f2d47cd6..73fd81635 100644
--- a/pkg/clmimicry/config.go
+++ b/pkg/clmimicry/config.go
@@ -37,6 +37,10 @@ type Config struct {
 
 	// Sharding is the configuration for event sharding
 	Sharding ShardingConfig `yaml:"sharding"`
+
+	// RandomSampling is the configuration for random sampling (second chance for events
+	// that were not captured by deterministic sharding)
+	RandomSampling RandomSamplingConfig `yaml:"randomSampling"`
 }
 
 func (c *Config) Validate() error {
@@ -62,6 +66,10 @@ func (c *Config) Validate() error {
 		return fmt.Errorf("invalid sharding config: %w", err)
 	}
 
+	if err := c.validateRandomSampling(); err != nil {
+		return fmt.Errorf("invalid random sampling config: %w", err)
+	}
+
 	return nil
 }
 
@@ -116,6 +124,27 @@ func (c *Config) validateSharding() error {
 	return nil
 }
 
+// validateRandomSampling validates the random sampling configuration
+func (c *Config) validateRandomSampling() error {
+	// If random sampling is not configured, that's fine - it's optional
+	if c.RandomSampling.Patterns == nil {
+		c.RandomSampling.Patterns = make(map[string]*RandomSamplingPatternConfig)
+
+		return nil
+	}
+
+	// Compile and validate patterns
+	if err := c.RandomSampling.compilePatterns(); err != nil {
+		return fmt.Errorf("failed to compile random sampling patterns: %w", err)
+	}
+
+	if err := c.RandomSampling.validate(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 // ApplyOverrides applies any overrides to the config.
 func (c *Config) ApplyOverrides(o *Override, log logrus.FieldLogger) error {
 	if o == nil {
diff --git a/pkg/clmimicry/event_libp2p_test.go b/pkg/clmimicry/event_libp2p_test.go
index 04480a915..cb75dbd68 100644
--- a/pkg/clmimicry/event_libp2p_test.go
+++ b/pkg/clmimicry/event_libp2p_test.go
@@ -2784,7 +2784,8 @@ func createTestMimicry(t *testing.T, config *Config, sink output.Sink) *testMimi
 	if config.Sharding.Topics != nil || config.Sharding.NoShardingKeyEvents != nil {
 		// Use sharding from config
 		var err error
-		sharder, err = NewUnifiedSharder(&config.Sharding, true)
+
+		sharder, err = NewUnifiedSharder(&config.Sharding, nil, true)
 		if err != nil {
 			t.Fatalf("Failed to create sharder: %v", err)
 		}
diff --git a/pkg/clmimicry/gossipsub_data_column_sidecar_test.go b/pkg/clmimicry/gossipsub_data_column_sidecar_test.go
index 1c900446c..00b3c79c4 100644
--- a/pkg/clmimicry/gossipsub_data_column_sidecar_test.go
+++ b/pkg/clmimicry/gossipsub_data_column_sidecar_test.go
@@ -312,7 +312,8 @@ func createTestMimicryWithWallclock(t *testing.T, config *Config, sink output.Si
 	var sharder *UnifiedSharder
 	if config.Sharding.Topics != nil || config.Sharding.NoShardingKeyEvents != nil {
 		var err error
-		sharder, err = NewUnifiedSharder(&config.Sharding, true)
+
+		sharder, err = NewUnifiedSharder(&config.Sharding, nil, true)
 		if err != nil {
 			t.Fatalf("Failed to create sharder: %v", err)
 		}
diff --git a/pkg/clmimicry/random_sampling.go b/pkg/clmimicry/random_sampling.go
new file mode 100644
index 000000000..a7ce61955
--- /dev/null
+++ b/pkg/clmimicry/random_sampling.go
@@ -0,0 +1,272 @@
+package clmimicry
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"github.com/ethpandaops/xatu/pkg/proto/xatu"
+)
+
+// RandomSamplingConfig represents random sampling configuration for events
+// that were not captured by deterministic sharding.
+type RandomSamplingConfig struct {
+	// Patterns maps event/topic patterns to their sampling chances.
+	// Key format: "EVENT_TYPE*:topic_pattern" or "EVENT_TYPE" (for GroupC events without topics)
+	Patterns map[string]*RandomSamplingPatternConfig `yaml:"patterns"`
+
+	// compiledPatterns holds compiled regex patterns for performance
+	compiledPatterns map[string]*CompiledRandomPattern
+}
+
+// RandomSamplingPatternConfig defines chance-based sampling for a pattern.
+type RandomSamplingPatternConfig struct {
+	// Chance is the probability as a percentage string (e.g., "2%", "0.5%")
+	Chance string `yaml:"chance"`
+
+	// parsedChance is the parsed float64 value (0.0 to 1.0)
+	parsedChance float64
+}
+
+// CompiledRandomPattern holds a compiled pattern with its config.
+type CompiledRandomPattern struct {
+	// Pattern is the compiled regex for topic matching (nil for GroupC patterns)
+	Pattern *regexp.Regexp
+
+	// Config is the associated sampling configuration
+	Config *RandomSamplingPatternConfig
+
+	// EventTypeConstraint specifies which event types this pattern applies to.
+	// Empty string means it applies to all events.
+	// Can be an exact event name (e.g., "LIBP2P_TRACE_RPC_META_CONTROL_IWANT")
+	// or a wildcard pattern (e.g., "LIBP2P_TRACE_RPC_META_*")
+	EventTypeConstraint string
+
+	// IsGroupCPattern is true if this is an event-type-only pattern (no topic regex)
+	IsGroupCPattern bool
+}
+
+// parseChancePercentage parses strings like "2%", "0.5%", "100%" to a float64 in range 0.0-1.0.
+func parseChancePercentage(chance string) (float64, error) {
+	chance = strings.TrimSpace(chance)
+
+	if !strings.HasSuffix(chance, "%") {
+		return 0, fmt.Errorf("chance must end with '%%', got '%s'", chance)
+	}
+
+	valueStr := strings.TrimSuffix(chance, "%")
+
+	value, err := strconv.ParseFloat(valueStr, 64)
+	if err != nil {
+		return 0, fmt.Errorf("invalid percentage value '%s': %w", valueStr, err)
+	}
+
+	if value < 0 || value > 100 {
+		return 0, fmt.Errorf("percentage must be between 0 and 100, got %.2f", value)
+	}
+
+	return value / 100.0, nil
+}
+
+// isValidEventTypeName checks if a string looks like an event type name.
+// Event types start with uppercase letters and contain underscores.
+func isValidEventTypeName(s string) bool {
+	if s == "" {
+		return false
+	}
+
+	// Must start with uppercase letter
+	if s[0] < 'A' || s[0] > 'Z' {
+		return false
+	}
+
+	// Must contain underscore
+	return strings.Contains(s, "_")
+}
+
+// compilePatterns compiles all regex patterns in the configuration.
+func (c *RandomSamplingConfig) compilePatterns() error {
+	if c.Patterns == nil {
+		c.Patterns = make(map[string]*RandomSamplingPatternConfig)
+
+		return nil
+	}
+
+	c.compiledPatterns = make(map[string]*CompiledRandomPattern, len(c.Patterns))
+
+	for pattern, config := range c.Patterns {
+		// Parse the chance percentage
+		parsedChance, err := parseChancePercentage(config.Chance)
+		if err != nil {
+			return fmt.Errorf("invalid chance '%s' for pattern '%s': %w",
+				config.Chance, pattern, err)
+		}
+
+		config.parsedChance = parsedChance
+
+		// Check if this is a GroupC event-type-only pattern (no colon separator).
+		// GroupC patterns don't have a colon (e.g., "LIBP2P_TRACE_RPC_META_CONTROL_IWANT")
+		if !strings.Contains(pattern, ":") && isValidEventTypeName(pattern) {
+			c.compiledPatterns[pattern] = &CompiledRandomPattern{
+				Pattern:             nil, // No regex needed for event-type-only match
+				Config:              config,
+				EventTypeConstraint: pattern,
+				IsGroupCPattern:     true,
+			}
+
+			continue
+		}
+
+		// Parse EVENT_TYPE:topic_pattern format (same as existing sharding)
+		var (
+			eventTypeConstraint string
+			topicPattern        string
+		)
+
+		if colonIdx := strings.Index(pattern, ":"); colonIdx != -1 {
+			potentialEventType := pattern[:colonIdx]
+			// Check if it looks like an event type (starts with uppercase letter and contains underscore)
+			if potentialEventType != "" &&
+				potentialEventType[0] >= 'A' && potentialEventType[0] <= 'Z' &&
+				strings.Contains(potentialEventType, "_") {
+				// Extract event type constraint and topic pattern
+				eventTypeConstraint = potentialEventType
+				topicPattern = pattern[colonIdx+1:]
+			} else {
+				// Colon is part of the regex pattern, not an event type separator
+				eventTypeConstraint = ""
+				topicPattern = pattern
+			}
+		} else {
+			// No event type prefix, pattern applies to all events
+			eventTypeConstraint = ""
+			topicPattern = pattern
+		}
+
+		// Compile the topic pattern as regex
+		compiled, err := regexp.Compile(topicPattern)
+		if err != nil {
+			return fmt.Errorf("invalid regex pattern '%s': %w", topicPattern, err)
+		}
+
+		c.compiledPatterns[pattern] = &CompiledRandomPattern{
+			Pattern:             compiled,
+			Config:              config,
+			EventTypeConstraint: eventTypeConstraint,
+			IsGroupCPattern:     false,
+		}
+	}
+
+	return nil
+}
+
+// validate validates the random sampling configuration.
+func (c *RandomSamplingConfig) validate() error {
+	for pattern, config := range c.Patterns {
+		if config.Chance == "" {
+			return fmt.Errorf("chance is required for pattern '%s'", pattern)
+		}
+
+		if config.parsedChance < 0 || config.parsedChance > 1.0 {
+			return fmt.Errorf("invalid parsed chance %.4f for pattern '%s'",
+				config.parsedChance, pattern)
+		}
+	}
+
+	return nil
+}
+
+// findMatchingPattern finds the matching random sampling pattern for a given topic and event type.
+// Returns nil if no pattern matches.
+func (c *RandomSamplingConfig) findMatchingPattern(
+	topic string,
+	eventType xatu.Event_Name,
+) *RandomSamplingPatternConfig {
+	if len(c.compiledPatterns) == 0 {
+		return nil
+	}
+
+	eventTypeName := eventType.String()
+
+	// For GroupC events (no topic), check event-type-only patterns first
+	if topic == "" {
+		// Try exact match on event type name
+		if compiled, exists := c.compiledPatterns[eventTypeName]; exists && compiled.IsGroupCPattern {
+			return compiled.Config
+		}
+
+		// Check wildcard event type patterns for GroupC
+		for _, compiled := range c.compiledPatterns {
+			if !compiled.IsGroupCPattern {
+				continue
+			}
+
+			// Check wildcard match (e.g., "LIBP2P_TRACE_RPC_META_*")
+			if strings.HasSuffix(compiled.EventTypeConstraint, "*") {
+				prefix := strings.TrimSuffix(compiled.EventTypeConstraint, "*")
+				if strings.HasPrefix(eventTypeName, prefix) {
+					return compiled.Config
+				}
+			}
+		}
+	}
+
+	// Find the best matching pattern (select highest chance when multiple match)
+	var bestMatch *RandomSamplingPatternConfig
+
+	var bestChance float64
+
+	for _, compiled := range c.compiledPatterns {
+		if compiled.IsGroupCPattern {
+			continue // Already handled above for GroupC
+		}
+
+		// Check topic pattern match
+		if compiled.Pattern != nil && !compiled.Pattern.MatchString(topic) {
+			continue
+		}
+
+		// Check event type constraint
+		if compiled.EventTypeConstraint != "" {
+			// Check for wildcard match (e.g., "LIBP2P_TRACE_RPC_META_*")
+			if strings.HasSuffix(compiled.EventTypeConstraint, "*") {
+				prefix := strings.TrimSuffix(compiled.EventTypeConstraint, "*")
+				if !strings.HasPrefix(eventTypeName, prefix) {
+					continue
+				}
+			} else if eventTypeName != compiled.EventTypeConstraint {
+				// Exact match required
+				continue
+			}
+		}
+
+		// Select pattern with highest chance (consistent with existing sharding behavior)
+		if bestMatch == nil || compiled.Config.parsedChance > bestChance {
+			bestMatch = compiled.Config
+			bestChance = compiled.Config.parsedChance
+		}
+	}
+
+	return bestMatch
+}
+
+// GetParsedChance returns the parsed chance value (0.0 to 1.0).
+func (c *RandomSamplingPatternConfig) GetParsedChance() float64 {
+	return c.parsedChance
+}
+
+// LogSummary returns a human-readable summary of the random sampling configuration.
+func (c *RandomSamplingConfig) LogSummary() string {
+	if len(c.Patterns) == 0 {
+		return "Random sampling disabled (no patterns configured)"
+	}
+
+	summary := fmt.Sprintf("Random sampling enabled with %d patterns:", len(c.Patterns))
+
+	for pattern, config := range c.Patterns {
+		summary += fmt.Sprintf("\n  - Pattern '%s': %s chance", pattern, config.Chance)
+	}
+
+	return summary
+}
diff --git a/pkg/clmimicry/random_sampling_test.go b/pkg/clmimicry/random_sampling_test.go
new file mode 100644
index 000000000..953adb385
--- /dev/null
+++ b/pkg/clmimicry/random_sampling_test.go
@@ -0,0 +1,679 @@
+package clmimicry
+
+import (
+	"testing"
+
+	"github.com/ethpandaops/xatu/pkg/proto/xatu"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+const testMsgIDBase = "test-msg-id"
+
+func TestParseChancePercentage(t *testing.T) {
+	tests := []struct {
+		name      string
+		input     string
+		expected  float64
+		wantError bool
+	}{
+		{
+			name:      "2 percent",
+			input:     "2%",
+			expected:  0.02,
+			wantError: false,
+		},
+		{
+			name:      "0.5 percent",
+			input:     "0.5%",
+			expected:  0.005,
+			wantError: false,
+		},
+		{
+			name:      "100 percent",
+			input:     "100%",
+			expected:  1.0,
+			wantError: false,
+		},
+		{
+			name:      "0 percent",
+			input:     "0%",
+			expected:  0.0,
+			wantError: false,
+		},
+		{
+			name:      "50 percent",
+			input:     "50%",
+			expected:  0.5,
+			wantError: false,
+		},
+		{
+			name:      "2.5 percent",
+			input:     "2.5%",
+			expected:  0.025,
+			wantError: false,
+		},
+		{
+			name:      "with spaces",
+			input:     "  10%  ",
+			expected:  0.1,
+			wantError: false,
+		},
+		{
+			name:      "missing percent sign",
+			input:     "2",
+			expected:  0,
+			wantError: true,
+		},
+		{
+			name:      "invalid value",
+			input:     "invalid%",
+			expected:  0,
+			wantError: true,
+		},
+		{
+			name:      "over 100 percent",
+			input:     "101%",
+			expected:  0,
+			wantError: true,
+		},
+		{
+			name:      "negative percent",
+			input:     "-5%",
+			expected:  0,
+			wantError: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := parseChancePercentage(tt.input)
+			if tt.wantError {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+				assert.InDelta(t, tt.expected, result, 0.0001)
+			}
+		})
+	}
+}
+
+func TestIsValidEventTypeName(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected bool
+	}{
+		{
+			name:     "valid event type",
+			input:    "LIBP2P_TRACE_RPC_META_CONTROL_IWANT",
+			expected: true,
+		},
+		{
+			name:     "valid with wildcard",
+			input:    "LIBP2P_TRACE_*",
+			expected: true,
+		},
+		{
+			name:     "empty string",
+			input:    "",
+			expected: false,
+		},
+		{
+			name:     "lowercase",
+			input:    "libp2p_trace",
+			expected: false,
+		},
+		{
+			name:     "no underscore",
+			input:    "LIBP2PTRACE",
+			expected: false,
+		},
+		{
+			name:     "regex pattern",
+			input:    ".*beacon.*",
+			expected: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := isValidEventTypeName(tt.input)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+func TestRandomSamplingConfigCompilePatterns(t *testing.T) {
+	tests := []struct {
+		name      string
+		config    RandomSamplingConfig
+		wantError bool
+	}{
+		{
+			name: "valid GroupC pattern",
+			config: RandomSamplingConfig{
+				Patterns: map[string]*RandomSamplingPatternConfig{
+					"LIBP2P_TRACE_RPC_META_CONTROL_IWANT": {Chance: "2%"},
+				},
+			},
+			wantError: false,
+		},
+		{
+			name: "valid GroupA/B pattern with topic",
+			config: RandomSamplingConfig{
+				Patterns: map[string]*RandomSamplingPatternConfig{
+					"LIBP2P_TRACE_RPC_META_CONTROL_IHAVE*:.*attestation.*": {Chance: "5%"},
+				},
+			},
+			wantError: false,
+		},
+		{
+			name: "valid topic-only pattern",
+			config: RandomSamplingConfig{
+				Patterns: map[string]*RandomSamplingPatternConfig{
+					".*beacon_block.*": {Chance: "10%"},
+				},
+			},
+			wantError: false,
+		},
+		{
+			name: "multiple patterns",
+			config: RandomSamplingConfig{
+				Patterns: map[string]*RandomSamplingPatternConfig{
+					"LIBP2P_TRACE_RPC_META_CONTROL_IWANT":                  {Chance: "2%"},
+					"LIBP2P_TRACE_RPC_META_CONTROL_IHAVE*:.*attestation.*": {Chance: "5%"},
+					".*": {Chance: "0.5%"},
+				},
+			},
+			wantError: false,
+		},
+		{
+			name: "invalid chance format",
+			config: RandomSamplingConfig{
+				Patterns: map[string]*RandomSamplingPatternConfig{
+					"LIBP2P_TRACE_RPC_META_CONTROL_IWANT": {Chance: "invalid"},
+				},
+			},
+			wantError: true,
+		},
+		{
+			name: "invalid regex pattern",
+			config: RandomSamplingConfig{
+				Patterns: map[string]*RandomSamplingPatternConfig{
+					"LIBP2P_TRACE_*:[invalid(": {Chance: "2%"},
+				},
+			},
+			wantError: true,
+		},
+		{
+			name:      "nil patterns",
+			config:    RandomSamplingConfig{},
+			wantError: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := tt.config.compilePatterns()
+			if tt.wantError {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+}
+
+func TestRandomSamplingFindMatchingPattern(t *testing.T) {
+	config := RandomSamplingConfig{
+		Patterns: map[string]*RandomSamplingPatternConfig{
+			"LIBP2P_TRACE_RPC_META_CONTROL_IWANT":                  {Chance: "2%"},
+			"LIBP2P_TRACE_RPC_META_CONTROL_IHAVE*:.*attestation.*": {Chance: "5%"},
+			".*beacon_block.*":                                     {Chance: "10%"},
+		},
+	}
+
+	err := config.compilePatterns()
+	require.NoError(t, err)
+
+	tests := []struct {
+		name           string
+		topic          string
+		eventType      xatu.Event_Name
+		expectMatch    bool
+		expectedChance float64
+	}{
+		{
+			name:           "GroupC IWANT match - no topic",
+			topic:          "",
+			eventType:      xatu.Event_LIBP2P_TRACE_RPC_META_CONTROL_IWANT,
+			expectMatch:    true,
+			expectedChance: 0.02,
+		},
+		{
+			name:           "GroupA IHAVE match with attestation topic",
+			topic:          "/eth2/mainnet/beacon_attestation/1/ssz_snappy",
+			eventType:      xatu.Event_LIBP2P_TRACE_RPC_META_CONTROL_IHAVE,
+			expectMatch:    true,
+			expectedChance: 0.05,
+		},
+		{
+			name:           "Topic pattern match for beacon block",
+			topic:          "/eth2/mainnet/beacon_block/ssz_snappy",
+			eventType:      xatu.Event_LIBP2P_TRACE_GOSSIPSUB_BEACON_BLOCK,
+			expectMatch:    true,
+			expectedChance: 0.10,
+		},
+		{
+			name:        "No match for unrelated event type and topic",
+			topic:       "/eth2/mainnet/sync_committee/1/ssz_snappy",
+			eventType:   xatu.Event_LIBP2P_TRACE_GOSSIPSUB_BEACON_ATTESTATION,
+			expectMatch: false,
+		},
+		{
+			name:        "GroupC IDONTWANT - no match",
+			topic:       "",
+			eventType:   xatu.Event_LIBP2P_TRACE_RPC_META_CONTROL_IDONTWANT,
+			expectMatch: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := config.findMatchingPattern(tt.topic, tt.eventType)
+			if tt.expectMatch {
+				require.NotNil(t, result)
+				assert.InDelta(t, tt.expectedChance, result.parsedChance, 0.0001)
+			} else {
+				assert.Nil(t, result)
+			}
+		})
+	}
+}
+
+func TestRandomSamplingNoDuplicates(t *testing.T) {
+	// Test that when deterministic sharding accepts an event,
+	// random sampling is NOT invoked (no duplicates)
+	shardingConfig := &ShardingConfig{
+		Topics: map[string]*TopicShardingConfig{
+			".*": {
+				TotalShards:  1,
+				ActiveShards: []uint64{0}, // 100% deterministic sampling
+			},
+		},
+	}
+
+	err := shardingConfig.compilePatterns()
+	require.NoError(t, err)
+
+	randomConfig := &RandomSamplingConfig{
+		Patterns: map[string]*RandomSamplingPatternConfig{
+			".*": {Chance: "100%"}, // 100% random sampling
+		},
+	}
+
+	err = randomConfig.compilePatterns()
+	require.NoError(t, err)
+
+	sharder, err := NewUnifiedSharder(shardingConfig, randomConfig, true)
+	require.NoError(t, err)
+
+	// Should be accepted by deterministic sharding
+	// The reason should NOT contain "random"
+	shouldProcess, reason := sharder.ShouldProcess(
+		xatu.Event_LIBP2P_TRACE_GOSSIPSUB_BEACON_BLOCK,
+		"test-msg-id",
+		"/eth2/mainnet/beacon_block/ssz_snappy",
+	)
+
+	assert.True(t, shouldProcess)
+	assert.NotContains(t, reason, "random")
+	assert.Contains(t, reason, "group_a")
+}
+
+func TestRandomSamplingSecondChance(t *testing.T) {
+	// Test that when deterministic sharding rejects an event,
+	// random sampling is tried
+	//
+	// We configure deterministic sharding to only accept shard 511,
+	// and use a message ID that we know hashes to a different shard.
+	shardingConfig := &ShardingConfig{
+		Topics: map[string]*TopicShardingConfig{
+			".*": {
+				TotalShards:  512,
+				ActiveShards: []uint64{511}, // Only shard 511 is active
+			},
+		},
+	}
+
+	err := shardingConfig.compilePatterns()
+	require.NoError(t, err)
+
+	randomConfig := &RandomSamplingConfig{
+		Patterns: map[string]*RandomSamplingPatternConfig{
+			".*": {Chance: "100%"}, // 100% random sampling
+		},
+	}
+
+	err = randomConfig.compilePatterns()
+	require.NoError(t, err)
+
+	sharder, err := NewUnifiedSharder(shardingConfig, randomConfig, true)
+	require.NoError(t, err)
+
+	// Find a message ID that doesn't hash to shard 511
+	testMsgID := testMsgIDBase
+	for GetShard(testMsgID, 512) == 511 {
+		testMsgID = testMsgID + "x"
+	}
+
+	// Deterministic should reject (msgID doesn't hash to shard 511)
+	// Random sampling at 100% should accept
+	shouldProcess, reason := sharder.ShouldProcess(
+		xatu.Event_LIBP2P_TRACE_GOSSIPSUB_BEACON_BLOCK,
+		testMsgID,
+		"/eth2/mainnet/beacon_block/ssz_snappy",
+	)
+
+	assert.True(t, shouldProcess)
+	assert.Contains(t, reason, "random_sampled")
+}
+
+func TestRandomSamplingGroupC(t *testing.T) {
+	// Test GroupC events (IWANT) work with random sampling
+	shardingConfig := &ShardingConfig{
+		Topics: map[string]*TopicShardingConfig{
+			"LIBP2P_TRACE_RPC_META_CONTROL_IWANT": {
+				TotalShards:  512,
+				ActiveShards: []uint64{511}, // Only shard 511 is active
+			},
+		},
+	}
+
+	err := shardingConfig.compilePatterns()
+	require.NoError(t, err)
+
+	randomConfig := &RandomSamplingConfig{
+		Patterns: map[string]*RandomSamplingPatternConfig{
+			"LIBP2P_TRACE_RPC_META_CONTROL_IWANT": {Chance: "100%"},
+		},
+	}
+
+	err = randomConfig.compilePatterns()
+	require.NoError(t, err)
+
+	sharder, err := NewUnifiedSharder(shardingConfig, randomConfig, true)
+	require.NoError(t, err)
+
+	// Find a message ID that doesn't hash to shard 511
+	testMsgID := testMsgIDBase
+	for GetShard(testMsgID, 512) == 511 {
+		testMsgID = testMsgID + "x"
+	}
+
+	// GroupC event with no topic - should be accepted by random sampling
+	shouldProcess, reason := sharder.ShouldProcess(
+		xatu.Event_LIBP2P_TRACE_RPC_META_CONTROL_IWANT,
+		testMsgID,
+		"", // GroupC events have no topic
+	)
+
+	assert.True(t, shouldProcess)
+	assert.Contains(t, reason, "random_sampled")
+}
+
+func TestRandomSamplingDisabled(t *testing.T) {
+	// Test that when random sampling config is nil, it doesn't affect deterministic
+	shardingConfig := &ShardingConfig{
+		Topics: map[string]*TopicShardingConfig{
+			".*": {
+				TotalShards:  1,
+				ActiveShards: []uint64{0}, // 100% deterministic
+			},
+		},
+	}
+
+	err := shardingConfig.compilePatterns()
+	require.NoError(t, err)
+
+	// No random sampling config
+	sharder, err := NewUnifiedSharder(shardingConfig, nil, true)
+	require.NoError(t, err)
+
+	assert.False(t, sharder.randomSamplingEnabled)
+
+	shouldProcess, reason := sharder.ShouldProcess(
+		xatu.Event_LIBP2P_TRACE_GOSSIPSUB_BEACON_BLOCK,
+		"test-msg-id",
+		"/eth2/mainnet/beacon_block/ssz_snappy",
+	)
+
+	assert.True(t, shouldProcess)
+	assert.NotContains(t, reason, "random")
+}
+
+func TestRandomSamplingDistribution(t *testing.T) {
+	// Statistical test to verify approximate random sampling rate
+	shardingConfig := &ShardingConfig{
+		Topics: map[string]*TopicShardingConfig{
+			".*": {
+				TotalShards:  512,
+				ActiveShards: []uint64{511}, // Only shard 511 is active
+			},
+		},
+	}
+
+	err := shardingConfig.compilePatterns()
+	require.NoError(t, err)
+
+	randomConfig := &RandomSamplingConfig{
+		Patterns: map[string]*RandomSamplingPatternConfig{
+			".*": {Chance: "10%"}, // 10% random sampling
+		},
+	}
+
+	err = randomConfig.compilePatterns()
+	require.NoError(t, err)
+
+	sharder, err := NewUnifiedSharder(shardingConfig, randomConfig, true)
+	require.NoError(t, err)
+
+	// Find a message ID that doesn't hash to shard 511
+	testMsgID := testMsgIDBase
+	for GetShard(testMsgID, 512) == 511 {
+		testMsgID = testMsgID + "x"
+	}
+
+	// Run many trials
+	const trials = 10000
+
+	accepted := 0
+
+	for i := 0; i < trials; i++ {
+		shouldProcess, _ := sharder.ShouldProcess(
+			xatu.Event_LIBP2P_TRACE_GOSSIPSUB_BEACON_BLOCK,
+			testMsgID, // Same msgID that deterministic always rejects
+			"/eth2/mainnet/beacon_block/ssz_snappy",
+		)
+		if shouldProcess {
+			accepted++
+		}
+	}
+
+	// With 10% sampling, we expect ~1000 accepted out of 10000
+	// Allow for statistical variance (8% to 12%)
+	acceptedRate := float64(accepted) / float64(trials)
+	assert.InDelta(t, 0.10, acceptedRate, 0.02, "Expected ~10%% acceptance rate, got %.2f%%", acceptedRate*100)
+}
+
+func TestRandomSamplingWildcardEventType(t *testing.T) {
+	// Test that wildcard event type patterns match multiple event types
+	config := RandomSamplingConfig{
+		Patterns: map[string]*RandomSamplingPatternConfig{
+			"LIBP2P_TRACE_RPC_META_*:.*attestation.*": {Chance: "100%"},
+		},
+	}
+
+	err := config.compilePatterns()
+	require.NoError(t, err)
+
+	topic := "/eth2/mainnet/beacon_attestation/1/ssz_snappy"
+
+	// Should match IHAVE
+	result := config.findMatchingPattern(topic, xatu.Event_LIBP2P_TRACE_RPC_META_CONTROL_IHAVE)
+	require.NotNil(t, result, "IHAVE should match wildcard pattern")
+
+	// Should match IWANT (even though it's GroupC, the wildcard should still match the event type)
+	result = config.findMatchingPattern(topic, xatu.Event_LIBP2P_TRACE_RPC_META_CONTROL_IWANT)
+	require.NotNil(t, result, "IWANT should match wildcard pattern")
+
+	// Should NOT match GOSSIPSUB events
+	result = config.findMatchingPattern(topic, xatu.Event_LIBP2P_TRACE_GOSSIPSUB_BEACON_ATTESTATION)
+	assert.Nil(t, result, "GOSSIPSUB should not match RPC_META wildcard")
+}
+
+func TestRandomSamplingZeroPercent(t *testing.T) {
+	// Test that 0% chance never accepts
+	shardingConfig := &ShardingConfig{
+		Topics: map[string]*TopicShardingConfig{
+			".*": {
+				TotalShards:  512,
+				ActiveShards: []uint64{511}, // Only shard 511 is active
+			},
+		},
+	}
+
+	err := shardingConfig.compilePatterns()
+	require.NoError(t, err)
+
+	randomConfig := &RandomSamplingConfig{
+		Patterns: map[string]*RandomSamplingPatternConfig{
+			".*": {Chance: "0%"}, // 0% should never accept
+		},
+	}
+
+	err = randomConfig.compilePatterns()
+	require.NoError(t, err)
+
+	sharder, err := NewUnifiedSharder(shardingConfig, randomConfig, true)
+	require.NoError(t, err)
+
+	// Find a message ID that doesn't hash to shard 511
+	testMsgID := testMsgIDBase
+	for GetShard(testMsgID, 512) == 511 {
+		testMsgID = testMsgID + "x"
+	}
+
+	// Run many trials - none should be accepted
+	for i := 0; i < 1000; i++ {
+		shouldProcess, _ := sharder.ShouldProcess(
+			xatu.Event_LIBP2P_TRACE_GOSSIPSUB_BEACON_BLOCK,
+			testMsgID,
+			"/eth2/mainnet/beacon_block/ssz_snappy",
+		)
+		assert.False(t, shouldProcess, "0%% chance should never accept")
+	}
+}
+
+func TestRandomSamplingGroupB(t *testing.T) {
+	// Test that topic-only patterns work for random sampling
+	shardingConfig := &ShardingConfig{
+		Topics: map[string]*TopicShardingConfig{
+			".*": {
+				TotalShards:  512,
+				ActiveShards: []uint64{511}, // Only shard 511 is active
+			},
+		},
+	}
+
+	err := shardingConfig.compilePatterns()
+	require.NoError(t, err)
+
+	randomConfig := &RandomSamplingConfig{
+		Patterns: map[string]*RandomSamplingPatternConfig{
+			".*beacon_block.*": {Chance: "100%"}, // Topic-only pattern
+		},
+	}
+
+	err = randomConfig.compilePatterns()
+	require.NoError(t, err)
+
+	sharder, err := NewUnifiedSharder(shardingConfig, randomConfig, true)
+	require.NoError(t, err)
+
+	// Find a message ID that doesn't hash to shard 511
+	testMsgID := testMsgIDBase
+	for GetShard(testMsgID, 512) == 511 {
+		testMsgID = testMsgID + "x"
+	}
+
+	// Topic-only pattern should match based on topic
+	shouldProcess, reason := sharder.ShouldProcess(
+		xatu.Event_LIBP2P_TRACE_GOSSIPSUB_BEACON_BLOCK,
+		testMsgID,
+		"/eth2/mainnet/beacon_block/ssz_snappy",
+	)
+
+	assert.True(t, shouldProcess)
+	assert.Contains(t, reason, "random_sampled")
+}
+
+func TestRandomSamplingEmptyPatterns(t *testing.T) {
+	// Test that empty patterns map (not nil) disables random sampling
+	randomConfig := &RandomSamplingConfig{
+		Patterns: map[string]*RandomSamplingPatternConfig{}, // Empty, not nil
+	}
+
+	err := randomConfig.compilePatterns()
+	require.NoError(t, err)
+
+	shardingConfig := &ShardingConfig{
+		Topics: map[string]*TopicShardingConfig{
+			".*": {
+				TotalShards:  512,
+				ActiveShards: []uint64{511},
+			},
+		},
+	}
+
+	err = shardingConfig.compilePatterns()
+	require.NoError(t, err)
+
+	sharder, err := NewUnifiedSharder(shardingConfig, randomConfig, true)
+	require.NoError(t, err)
+
+	assert.False(t, sharder.randomSamplingEnabled, "Empty patterns should disable random sampling")
+}
+
+func TestRandomSamplingLogSummary(t *testing.T) {
+	tests := []struct {
+		name     string
+		config   RandomSamplingConfig
+		contains []string
+	}{
+		{
+			name:     "empty config",
+			config:   RandomSamplingConfig{},
+			contains: []string{"disabled"},
+		},
+		{
+			name: "with patterns",
+			config: RandomSamplingConfig{
+				Patterns: map[string]*RandomSamplingPatternConfig{
+					"LIBP2P_TRACE_RPC_META_CONTROL_IWANT": {Chance: "2%"},
+				},
+			},
+			contains: []string{"enabled", "1 patterns", "2%"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			summary := tt.config.LogSummary()
+			for _, substr := range tt.contains {
+				assert.Contains(t, summary, substr)
+			}
+		})
+	}
+}
diff --git a/pkg/clmimicry/sharding.go b/pkg/clmimicry/sharding.go
index d0532493f..b38cac030 100644
--- a/pkg/clmimicry/sharding.go
+++ b/pkg/clmimicry/sharding.go
@@ -2,6 +2,7 @@ package clmimicry
 
 import (
 	"fmt"
+	"math/rand/v2"
 	"regexp"
 	"sort"
 	"strconv"
@@ -18,9 +19,11 @@ const (
 
 // UnifiedSharder provides a single sharding decision point for all events
 type UnifiedSharder struct {
-	config           *ShardingConfig
-	eventCategorizer *EventCategorizer
-	enabled          bool
+	config                *ShardingConfig
+	randomSamplingConfig  *RandomSamplingConfig
+	eventCategorizer      *EventCategorizer
+	enabled               bool
+	randomSamplingEnabled bool
 }
 
 // ShardingConfig represents the sharding configuration
@@ -61,7 +64,11 @@ type CompiledPattern struct {
 }
 
 // NewUnifiedSharder creates a new unified sharder
-func NewUnifiedSharder(config *ShardingConfig, enabled bool) (*UnifiedSharder, error) {
+func NewUnifiedSharder(
+	config *ShardingConfig,
+	randomConfig *RandomSamplingConfig,
+	enabled bool,
+) (*UnifiedSharder, error) {
 	if config == nil {
 		config = &ShardingConfig{
 			Topics: make(map[string]*TopicShardingConfig),
@@ -81,14 +88,21 @@ func NewUnifiedSharder(config *ShardingConfig, enabled bool) (*UnifiedSharder, e
 		return nil, fmt.Errorf("invalid sharding config: %w", err)
 	}
 
+	// Check if random sampling is enabled
+	randomSamplingEnabled := randomConfig != nil && len(randomConfig.Patterns) > 0
+
 	return &UnifiedSharder{
-		config:           config,
-		eventCategorizer: NewEventCategorizer(),
-		enabled:          enabled,
+		config:                config,
+		randomSamplingConfig:  randomConfig,
+		eventCategorizer:      NewEventCategorizer(),
+		enabled:               enabled,
+		randomSamplingEnabled: randomSamplingEnabled,
 	}, nil
 }
 
-// ShouldProcess determines if an event should be processed based on sharding rules
+// ShouldProcess determines if an event should be processed based on sharding rules.
+// It first tries deterministic sharding, and if that rejects the event, it tries
+// random sampling as a "second chance" mechanism.
 //
 //nolint:gocritic // named returns unnecessary.
 func (s *UnifiedSharder) ShouldProcess(eventType xatu.Event_Name, msgID, topic string) (bool, string) {
@@ -96,6 +110,33 @@ func (s *UnifiedSharder) ShouldProcess(eventType xatu.Event_Name, msgID, topic s
 		return true, "sharding_disabled"
 	}
 
+	// Try deterministic sharding first
+	deterministicResult, deterministicReason := s.deterministicProcess(eventType, msgID, topic)
+
+	// If deterministic sharding accepted, return immediately (no duplicates)
+	if deterministicResult {
+		return true, deterministicReason
+	}
+
+	// Try random sampling as "second chance" if deterministic rejected
+	if s.randomSamplingEnabled {
+		randomResult, randomReason := s.randomSamplingProcess(eventType, topic)
+		if randomResult {
+			return true, randomReason
+		}
+	}
+
+	// Neither deterministic nor random sampling accepted
+	return false, deterministicReason
+}
+
+// deterministicProcess contains the deterministic sharding logic based on SipHash.
+//
+//nolint:gocritic // named returns unnecessary.
+func (s *UnifiedSharder) deterministicProcess(
+	eventType xatu.Event_Name,
+	msgID, topic string,
+) (bool, string) {
 	eventInfo, exists := s.eventCategorizer.GetEventInfo(eventType)
 	if !exists {
 		// Unknown event type - default to process
@@ -173,6 +214,33 @@ func (s *UnifiedSharder) ShouldProcess(eventType xatu.Event_Name, msgID, topic s
 	}
 }
 
+// randomSamplingProcess checks if random sampling should accept this event.
+// Returns true if the event should be processed based on random chance.
+//
+//nolint:gocritic // named returns unnecessary.
+func (s *UnifiedSharder) randomSamplingProcess(
+	eventType xatu.Event_Name,
+	topic string,
+) (bool, string) {
+	if s.randomSamplingConfig == nil {
+		return false, "random_sampling_not_configured"
+	}
+
+	// Find matching random sampling pattern
+	config := s.randomSamplingConfig.findMatchingPattern(topic, eventType)
+	if config == nil {
+		return false, "random_no_pattern_match"
+	}
+
+	// Roll the dice - rand.Float64() is thread-safe in math/rand/v2
+	//nolint:gosec // G404: crypto strength not needed for sampling
+	if rand.Float64() < config.parsedChance {
+		return true, fmt.Sprintf("random_sampled_%.2f_pct", config.parsedChance*100)
+	}
+
+	return false, fmt.Sprintf("random_not_sampled_%.2f_pct", config.parsedChance*100)
+}
+
 // ShouldProcessBatch determines which events in a batch should be processed
 // This is used for RPC meta events where we have multiple events to evaluate
 func (s *UnifiedSharder) ShouldProcessBatch(eventType xatu.Event_Name, events []ShardableEvent) []bool {
diff --git a/pkg/clmimicry/sharding_test.go b/pkg/clmimicry/sharding_test.go
index 2ceb4f238..0f7fccd7b 100644
--- a/pkg/clmimicry/sharding_test.go
+++ b/pkg/clmimicry/sharding_test.go
@@ -40,7 +40,7 @@ func TestConfigurableTotalShards(t *testing.T) {
 	assert.InDelta(t, 0.0039, config.Topics["large_shards"].GetSamplingRate(), 0.001)
 
 	// Test that sharding works with different totalShards
-	_, err = NewUnifiedSharder(config, true)
+	_, err = NewUnifiedSharder(config, nil, true)
 	require.NoError(t, err)
 
 	// Test that the same key produces different shards with different totalShards
@@ -251,7 +251,7 @@ func TestUnifiedSharder(t *testing.T) {
 			require.NoError(t, err)
 
 			// Create sharder
-			sharder, err := NewUnifiedSharder(tt.config, tt.name != "Sharding disabled")
+			sharder, err := NewUnifiedSharder(tt.config, nil, tt.name != "Sharding disabled")
 			require.NoError(t, err)
 
 			// Test sharding decision
@@ -284,7 +284,7 @@ func TestShardDistribution(t *testing.T) {
 	err := config.compilePatterns()
 	require.NoError(t, err)
 
-	sharder, err := NewUnifiedSharder(config, true)
+	sharder, err := NewUnifiedSharder(config, nil, true)
 	require.NoError(t, err)
 
 	// Test shard distribution using chi-squared test
@@ -533,7 +533,7 @@ func TestBatchProcessing(t *testing.T) {
 	err := config.compilePatterns()
 	require.NoError(t, err)
 
-	sharder, err := NewUnifiedSharder(config, true)
+	sharder, err := NewUnifiedSharder(config, nil, true)
 	require.NoError(t, err)
 
 	// Create batch of events
@@ -688,7 +688,7 @@ func TestEventTypeAwareSharding(t *testing.T) {
 		},
 	}
 
-	sharder, err := NewUnifiedSharder(config, true)
+	sharder, err := NewUnifiedSharder(config, nil, true)
 	require.NoError(t, err)
 
 	topic := "/eth2/12345678/beacon_attestation_1/ssz_snappy"
@@ -809,7 +809,7 @@ func TestBackwardCompatibility(t *testing.T) {
 		},
 	}
 
-	sharder, err := NewUnifiedSharder(config, true)
+	sharder, err := NewUnifiedSharder(config, nil, true)
 	require.NoError(t, err)
 
 	// Test that patterns without event constraints match all event types
@@ -844,7 +844,7 @@ func TestGroupCEventTypeOnlyPatterns(t *testing.T) {
 			},
 		}
 
-		sharder, err := NewUnifiedSharder(config, true)
+		sharder, err := NewUnifiedSharder(config, nil, true)
 		require.NoError(t, err)
 
 		// Test with multiple message IDs to verify 100% sampling
@@ -886,7 +886,7 @@ func TestGroupCEventTypeOnlyPatterns(t *testing.T) {
 			},
 		}
 
-		iwantSharder, err := NewUnifiedSharder(iwantConfig, true)
+		iwantSharder, err := NewUnifiedSharder(iwantConfig, nil, true)
 		require.NoError(t, err)
 
 		iwantProcessed := 0