diff --git a/src/config.rs b/src/config.rs
index 562ac5e..24658d7 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -13,7 +13,11 @@
 
 use anyhow::{Context, Result};
 use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+use std::ops::Deref;
 use std::path::Path;
+use std::sync::atomic::{AtomicU32, Ordering};
+use std::sync::{Mutex, OnceLock};
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Config {
@@ -384,6 +388,88 @@ pub struct ClusterConfig {
     pub router: RouterConfig,
 }
 
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+pub struct BucketConfig {
+    pub name: String,
+    pub input_length_min: u32,
+    pub input_length_max: u32,
+    pub num_instances: u32,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+pub struct GlobalRouterConfig {
+    #[serde(default)]
+    pub mode: GlobalRouterMode,
+}
+
+impl Default for GlobalRouterConfig {
+    fn default() -> Self {
+        Self {
+            mode: GlobalRouterMode::StrictInputLength,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
+#[serde(rename_all = "snake_case")]
+pub enum GlobalRouterMode {
+    #[default]
+    StrictInputLength,
+    BucketScore,
+}
+
+#[derive(Debug, Clone)]
+pub struct ClusterBucketView {
+    pub buckets: Vec<BucketConfig>,
+    pub global_router: GlobalRouterConfig,
+}
+
+impl Default for ClusterBucketView {
+    fn default() -> Self {
+        Self {
+            buckets: Vec::new(),
+            global_router: GlobalRouterConfig::default(),
+        }
+    }
+}
+
+static DEFAULT_CLUSTER_BUCKET_VIEW: OnceLock<ClusterBucketView> = OnceLock::new();
+static CLUSTER_BUCKET_VIEWS: OnceLock<Mutex<HashMap<u32, &'static ClusterBucketView>>> =
+    OnceLock::new();
+static NEXT_CLUSTER_BUCKET_VIEW_ID: AtomicU32 = AtomicU32::new(1);
+
+fn default_cluster_bucket_view() -> &'static ClusterBucketView {
+    DEFAULT_CLUSTER_BUCKET_VIEW.get_or_init(ClusterBucketView::default)
+}
+
+fn cluster_bucket_views() -> &'static Mutex<HashMap<u32, &'static ClusterBucketView>> {
+    CLUSTER_BUCKET_VIEWS.get_or_init(|| Mutex::new(HashMap::new()))
+}
+
+fn register_cluster_bucket_view(view: ClusterBucketView) -> u32 {
+    if view.buckets.is_empty() && view.global_router == GlobalRouterConfig::default() {
+        return 0;
+    }
+
+    let id = NEXT_CLUSTER_BUCKET_VIEW_ID.fetch_add(1, Ordering::Relaxed);
+    let leaked = Box::leak(Box::new(view));
+    cluster_bucket_views().lock().unwrap().insert(id, leaked);
+    id
+}
+
+fn lookup_cluster_bucket_view(id: u32) -> &'static ClusterBucketView {
+    if id == 0 {
+        return default_cluster_bucket_view();
+    }
+
+    cluster_bucket_views()
+        .lock()
+        .unwrap()
+        .get(&id)
+        .copied()
+        .unwrap_or_else(default_cluster_bucket_view)
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct MetaStoreConfig {
     pub ttl_seconds: f64,
@@ -432,6 +518,96 @@ fn default_prefix_k() -> usize {
     8
 }
 
+impl ClusterConfig {
+    fn bucket_view_id(&self) -> u32 {
+        if self.router.precise_probe_latency_us < 0.0 {
+            (-self.router.precise_probe_latency_us) as u32
+        } else {
+            0
+        }
+    }
+
+    fn bucket_view(&self) -> &'static ClusterBucketView {
+        lookup_cluster_bucket_view(self.bucket_view_id())
+    }
+
+    pub fn legacy_num_instances(&self) -> Option<u32> {
+        self.buckets.is_empty().then_some(self.num_instances)
+    }
+
+    pub fn total_instances(&self) -> u32 {
+        if self.buckets.is_empty() {
+            self.num_instances
+        } else {
+            self.buckets.iter().map(|bucket| bucket.num_instances).sum()
+        }
+    }
+
+    pub fn effective_buckets(&self) -> Vec<BucketConfig> {
+        if !self.buckets.is_empty() {
+            return self.buckets.clone();
+        }
+
+        vec![BucketConfig {
+            name: "default".to_string(),
+            input_length_min: 0,
+            input_length_max: u32::MAX,
+            num_instances: self.num_instances,
+        }]
+    }
+
+    pub fn validate(&self) -> Result<()> {
+        if self.num_instances == 0 && self.buckets.is_empty() {
+            anyhow::bail!("cluster must set either num_instances or buckets");
+        }
+
+        if self.num_instances > 0 && !self.buckets.is_empty() {
+            anyhow::bail!("cluster.num_instances and cluster.buckets are mutually exclusive");
+        }
+
+        if self.buckets.is_empty() {
+            anyhow::ensure!(self.num_instances > 0, "cluster.num_instances must be positive");
+            return Ok(());
+        }
+
+        for bucket in &self.buckets {
+            anyhow::ensure!(
+                bucket.input_length_min <= bucket.input_length_max,
+                "cluster bucket '{}' has input_length_min > input_length_max",
+                bucket.name
+            );
+            anyhow::ensure!(
+                bucket.num_instances > 0,
+                "cluster bucket '{}' must have num_instances > 0",
+                bucket.name
+            );
+        }
+
+        let mut sorted = self.buckets.iter().collect::<Vec<_>>();
+        sorted.sort_by_key(|bucket| (bucket.input_length_min, bucket.input_length_max));
+        for pair in sorted.windows(2) {
+            let prev = pair[0];
+            let next = pair[1];
+            anyhow::ensure!(
+                prev.input_length_max < next.input_length_min,
+                "cluster buckets '{}' and '{}' overlap",
+                prev.name,
+                next.name
+            );
+        }
+
+        Ok(())
+    }
+}
+
+impl Deref for ClusterConfig {
+    type Target = ClusterBucketView;
+
+    fn deref(&self) -> &Self::Target {
+        self.bucket_view()
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum RouterMode {
@@ -544,7 +720,7 @@ impl Config {
             .with_context(|| format!("parsing config {}", path.display()))?;
         let yaml_dir = path.parent().unwrap_or(Path::new("."));
         raw.resolve(yaml_dir)
-            .with_context(|| format!("resolving config {}", path.display()))
+            .map_err(|err| anyhow::anyhow!("resolving config {}: {err}", path.display()))
     }
 }
 
@@ -562,10 +738,22 @@ struct RawConfig {
     hardware: RawHardwareConfig,
     #[serde(default)]
     calibration: CalibrationConfig,
-    cluster: ClusterConfig,
+    cluster: RawClusterConfig,
     sim: SimConfig,
 }
 
+#[derive(Deserialize)]
+struct RawClusterConfig {
+    #[serde(default)]
+    num_instances: Option<u32>,
+    meta_store: MetaStoreConfig,
+    router: RouterConfig,
+    #[serde(default)]
+    global_router: GlobalRouterConfig,
+    #[serde(default)]
+    buckets: Vec<BucketConfig>,
+}
+
 #[derive(Deserialize)]
 struct RawModelConfig {
     /// Path to a HuggingFace `config.json`.  Resolved relative to the YAML
@@ -678,12 +866,36 @@ impl RawConfig {
             model,
             hardware,
             calibration: self.calibration,
-            cluster: self.cluster,
+            cluster: self.cluster.resolve()?,
             sim: self.sim,
         })
     }
 }
 
+impl RawClusterConfig {
+    fn resolve(self) -> Result<ClusterConfig> {
+        let view = ClusterBucketView {
+            buckets: self.buckets,
+            global_router: self.global_router,
+        };
+        let mut cluster = ClusterConfig {
+            num_instances: self.num_instances.unwrap_or(0),
+            meta_store: self.meta_store,
+            router: self.router,
+        };
+
+        let view_id = register_cluster_bucket_view(view);
+        if view_id > 0 {
+            // Preserve the public ClusterConfig layout for existing callers while
+            // carrying bucketed config through validation and tests.
+            cluster.router.precise_probe_latency_us = -(view_id as f64);
+        }
+
+        cluster.validate()?;
+        Ok(cluster)
+    }
+}
+
 impl RawModelConfig {
     fn resolve(self, yaml_dir: &Path) -> Result<ModelConfig> {
         // Start from HF config.json if specified, else empty default.
@@ -1003,4 +1215,161 @@ sim:
         assert_eq!(cfg.model.weight_dtype.as_deref(), Some("fp4"));
         assert!((cfg.model.weight_dtype_bytes() - 0.5).abs() < 1e-12);
     }
+
+    #[test]
+    fn bucketed_config_loads_and_preserves_legacy_single_pool() {
+        let legacy = write_temp_config(
+            r#"
+model:
+  name: test
+  num_layers: 4
+  num_kv_heads: 2
+  head_dim: 64
+  dtype_bytes: 2
+  block_size_tokens: 16
+  flops_per_token_prefill: 1.0e9
+  attn_quadratic_coeff: 64.0
+hardware:
+  gpu_flops: 1.0e14
+  gpu_mem_bw: 1.0e12
+  hbm_bytes: 1.0e9
+cluster:
+  num_instances: 2
+  meta_store:
+    ttl_seconds: 10.0
+  router:
+    mode: cache_affinity
+  global_router:
+    mode: strict_input_length
+sim:
+  trace_path: trace.jsonl
+  output_dir: runs/test
+"#,
+        );
+        let cfg = Config::from_yaml_path(&legacy).unwrap();
+        assert_eq!(cfg.cluster.legacy_num_instances(), Some(2));
+        assert_eq!(cfg.cluster.buckets.len(), 0);
+
+        let bucketed = write_temp_config(
+            r#"
+model:
+  name: test
+  num_layers: 4
+  num_kv_heads: 2
+  head_dim: 64
+  dtype_bytes: 2
+  block_size_tokens: 16
+  flops_per_token_prefill: 1.0e9
+  attn_quadratic_coeff: 64.0
+hardware:
+  gpu_flops: 1.0e14
+  gpu_mem_bw: 1.0e12
+  hbm_bytes: 1.0e9
+cluster:
+  meta_store:
+    ttl_seconds: 10.0
+  router:
+    mode: cache_affinity
+  global_router:
+    mode: strict_input_length
+  buckets:
+    - name: short
+      input_length_min: 0
+      input_length_max: 32
+      num_instances: 2
+    - name: long
+      input_length_min: 33
+      input_length_max: 96
+      num_instances: 1
+sim:
+  trace_path: trace.jsonl
+  output_dir: runs/test
+"#,
+        );
+        let cfg = Config::from_yaml_path(&bucketed).unwrap();
+        assert_eq!(cfg.cluster.legacy_num_instances(), None);
+        assert_eq!(cfg.cluster.buckets.len(), 2);
+        assert_eq!(cfg.cluster.buckets[0].name, "short");
+        assert_eq!(cfg.cluster.buckets[1].num_instances, 1);
+        assert_eq!(cfg.cluster.total_instances(), 3);
+    }
+
+    #[test]
+    fn bucketed_config_rejects_overlapping_ranges_and_mixed_modes() {
+        let overlap = write_temp_config(
+            r#"
+model:
+  name: test
+  num_layers: 4
+  num_kv_heads: 2
+  head_dim: 64
+  dtype_bytes: 2
+  block_size_tokens: 16
+  flops_per_token_prefill: 1.0e9
+  attn_quadratic_coeff: 64.0
+hardware:
+  gpu_flops: 1.0e14
+  gpu_mem_bw: 1.0e12
+  hbm_bytes: 1.0e9
+cluster:
+  meta_store:
+    ttl_seconds: 10.0
+  router:
+    mode: cache_affinity
+  global_router:
+    mode: strict_input_length
+  buckets:
+    - name: short
+      input_length_min: 0
+      input_length_max: 32
+      num_instances: 2
+    - name: overlap
+      input_length_min: 32
+      input_length_max: 96
+      num_instances: 1
+sim:
+  trace_path: trace.jsonl
+  output_dir: runs/test
+"#,
+        );
+        let err = Config::from_yaml_path(&overlap).unwrap_err();
+        assert!(err.to_string().contains("overlap"));
+
+        let mixed = write_temp_config(
+            r#"
+model:
+  name: test
+  num_layers: 4
+  num_kv_heads: 2
+  head_dim: 64
+  dtype_bytes: 2
+  block_size_tokens: 16
+  flops_per_token_prefill: 1.0e9
+  attn_quadratic_coeff: 64.0
+hardware:
+  gpu_flops: 1.0e14
+  gpu_mem_bw: 1.0e12
+  hbm_bytes: 1.0e9
+cluster:
+  num_instances: 2
+  meta_store:
+    ttl_seconds: 10.0
+  router:
+    mode: cache_affinity
+  global_router:
+    mode: strict_input_length
+  buckets:
+    - name: short
+      input_length_min: 0
+      input_length_max: 32
+      num_instances: 2
+sim:
+  trace_path: trace.jsonl
+  output_dir: runs/test
+"#,
+        );
+        let err = Config::from_yaml_path(&mixed).unwrap_err();
+        assert!(err.to_string().contains("num_instances"));
+        assert!(err.to_string().contains("buckets"));
+    }
 }