diff --git a/src/obikindex/src/lib.rs b/src/obikindex/src/lib.rs
index d6a0908..65df6c0 100644
--- a/src/obikindex/src/lib.rs
+++ b/src/obikindex/src/lib.rs
@@ -5,6 +5,7 @@ mod distance;
 mod dump;
 mod index;
 mod merge;
+mod rebuild;
 
 pub use error::{OKIError, OKIResult};
 pub use distance::{DistanceMetric, DistanceOutput};
diff --git a/src/obikindex/src/rebuild.rs b/src/obikindex/src/rebuild.rs
new file mode 100644
index 0000000..b360030
--- /dev/null
+++ b/src/obikindex/src/rebuild.rs
@@ -0,0 +1,116 @@
+use std::fs;
+use std::io;
+use std::path::Path;
+use std::time::Duration;
+
+use indicatif::{ProgressBar, ProgressStyle};
+use obikpartitionner::{KmerFilter, KmerPartition, MergeMode};
+use obisys::{Reporter, Stage};
+use rayon::prelude::*;
+use tracing::info;
+
+use crate::error::{OKIError, OKIResult};
+use crate::index::KmerIndex;
+use crate::meta::IndexMeta;
+use crate::state::{IndexState, SENTINEL_INDEXED};
+
+impl KmerIndex {
+    /// Rebuild `src` into a new compact single-layer index at `output`.
+    ///
+    /// Only k-mers whose per-genome row passes every filter in `filters` are
+    /// written. If `filters` is empty every k-mer is kept (pure compaction).
+    ///
+    /// `mode` controls whether the output stores counts or presence/absence.
+    /// A count source may be rebuilt in presence mode; a presence source
+    /// cannot be rebuilt in count mode.
+    pub fn rebuild<P: AsRef<Path>>(
+        output: P,
+        src: &KmerIndex,
+        filters: &[Box<dyn KmerFilter>],
+        mode: MergeMode,
+        force: bool,
+        rep: &mut Reporter,
+    ) -> OKIResult<Self> {
+        let output = output.as_ref();
+
+        if src.state() != IndexState::Indexed {
+            return Err(OKIError::NotIndexed(src.root_path.clone()));
+        }
+
+        if mode == MergeMode::Count && !src.meta.config.with_counts {
+            return Err(OKIError::InvalidInput(
+                "cannot rebuild in count mode from a presence-only source index".into(),
+            ));
+        }
+
+        if output.exists() {
+            if force {
+                fs::remove_dir_all(output)?;
+            } else {
+                return Err(OKIError::Io(io::Error::new(
+                    io::ErrorKind::AlreadyExists,
+                    format!("{}: output directory already exists", output.display()),
+                )));
+            }
+        }
+
+        // ── Create output directory + metadata ────────────────────────────────
+        fs::create_dir_all(output)?;
+        let mut meta = IndexMeta::new(src.meta.config.clone());
+        meta.config.with_counts = mode == MergeMode::Count;
+        meta.genomes = src.meta.genomes.clone();
+        meta.write(output)?;
+
+        let n_genomes = src.meta.genomes.len();
+        let n_partitions = src.partition.n_partitions();
+
+        // ── Create an empty destination KmerPartition ─────────────────────────
+        // Create the partitions/ subdirectory so KmerPartition::open_with_config works.
+        fs::create_dir_all(output.join(obikpartitionner::PARTITIONS_SUBDIR))?;
+        let dst_partition = KmerPartition::open_with_config(
+            output,
+            meta.config.kmer_size,
+            meta.config.minimizer_size,
+            meta.config.n_bits,
+        )?;
+
+        info!(
+            "rebuild: {} partition(s), {} genome(s), mode={:?}",
+            n_partitions, n_genomes, mode,
+        );
+
+        let t = Stage::start("rebuild");
+        let pb = ProgressBar::new(n_partitions as u64).with_style(
+            ProgressStyle::with_template("rebuild — [{bar:20}] {pos}/{len} | {msg}")
+                .unwrap()
+                .progress_chars("=> "),
+        );
+        pb.enable_steady_tick(Duration::from_millis(100));
+
+        let src_partition = &src.partition;
+
+        let errors: Vec<obiskio::SKError> = (0..n_partitions)
+            .into_par_iter()
+            .filter_map(|i| {
+                let result = dst_partition
+                    .rebuild_partition(src_partition, i, filters, mode, n_genomes)
+                    .err();
+                pb.inc(1);
+                result
+            })
+            .collect();
+
+        pb.finish_and_clear();
+
+        if let Some(e) = errors.into_iter().next() {
+            return Err(OKIError::Partition(e));
+        }
+
+        rep.push(t.stop());
+
+        // Write SENTINEL_INDEXED — output is ready to use.
+        fs::File::create(output.join(SENTINEL_INDEXED))?;
+
+        KmerIndex::open(output)
+    }
+}
diff --git a/src/obikmer/src/cmd/mod.rs b/src/obikmer/src/cmd/mod.rs
index ed66c65..ac4057e 100644
--- a/src/obikmer/src/cmd/mod.rs
+++ b/src/obikmer/src/cmd/mod.rs
@@ -2,5 +2,6 @@ pub mod distance;
 pub mod dump;
 pub mod index;
 pub mod merge;
+pub mod rebuild;
 pub mod superkmer;
 pub mod unitig;
diff --git a/src/obikmer/src/cmd/rebuild.rs b/src/obikmer/src/cmd/rebuild.rs
new file mode 100644
index 0000000..f172811
--- /dev/null
+++ b/src/obikmer/src/cmd/rebuild.rs
@@ -0,0 +1,111 @@
+use std::path::PathBuf;
+
+use clap::Args;
+use obikindex::{KmerIndex, MergeMode};
+use obikpartitionner::filter::{
+    KmerFilter, MaxGenomeCount, MaxGenomeFraction, MaxTotalCount,
+    MinGenomeCount, MinGenomeFraction, MinTotalCount,
+};
+use obisys::Reporter;
+use obikseq::{set_k, set_m};
+use tracing::info;
+
+#[derive(Args)]
+pub struct RebuildArgs {
+    /// Source index directory
+    pub source: PathBuf,
+
+    /// Output index directory
+    #[arg(short, long)]
+    pub output: PathBuf,
+
+    /// Minimum fraction of genomes containing the k-mer [0.0–1.0]
+    #[arg(long)]
+    pub min_quorum_frac: Option<f64>,
+
+    /// Maximum fraction of genomes containing the k-mer [0.0–1.0]
+    #[arg(long)]
+    pub max_quorum_frac: Option<f64>,
+
+    /// Minimum number of genomes containing the k-mer
+    #[arg(long)]
+    pub min_quorum_count: Option<usize>,
+
+    /// Maximum number of genomes containing the k-mer
+    #[arg(long)]
+    pub max_quorum_count: Option<usize>,
+
+    /// Minimum total count across all genomes (count index only)
+    #[arg(long)]
+    pub min_total_count: Option<u32>,
+
+    /// Maximum total count across all genomes (count index only)
+    #[arg(long)]
+    pub max_total_count: Option<u32>,
+
+    /// Per-genome count threshold for presence in quorum filters (default 0)
+    #[arg(long, default_value = "0")]
+    pub presence_threshold: u32,
+
+    /// Output as presence/absence instead of counts
+    #[arg(long)]
+    pub presence: bool,
+
+    /// Overwrite existing output directory
+    #[arg(short, long)]
+    pub force: bool,
+}
+
+pub fn run(args: RebuildArgs) {
+    let src = KmerIndex::open(&args.source).unwrap_or_else(|e| {
+        eprintln!("error opening source index: {e}");
+        std::process::exit(1);
+    });
+
+    set_k(src.kmer_size());
+    set_m(src.minimizer_size());
+
+    let n_genomes = src.meta().genomes.len();
+    let mode = if args.presence || !src.meta().config.with_counts {
+        MergeMode::Presence
+    } else {
+        MergeMode::Count
+    };
+
+    info!(
+        "rebuild: {} genome(s), mode={:?}, source={}",
+        n_genomes, mode, args.source.display()
+    );
+
+    let pt = args.presence_threshold;
+    let mut filters: Vec<Box<dyn KmerFilter>> = Vec::new();
+
+    if let Some(v) = args.min_quorum_frac {
+        filters.push(Box::new(MinGenomeFraction { frac: v, threshold: pt }));
+    }
+    if let Some(v) = args.max_quorum_frac {
+        filters.push(Box::new(MaxGenomeFraction { frac: v, threshold: pt }));
+    }
+    if let Some(v) = args.min_quorum_count {
+        filters.push(Box::new(MinGenomeCount { count: v, threshold: pt }));
+    }
+    if let Some(v) = args.max_quorum_count {
+        filters.push(Box::new(MaxGenomeCount { count: v, threshold: pt }));
+    }
+    if let Some(v) = args.min_total_count {
+        filters.push(Box::new(MinTotalCount { total: v }));
+    }
+    if let Some(v) = args.max_total_count {
+        filters.push(Box::new(MaxTotalCount { total: v }));
+    }
+
+    let mut rep = Reporter::new();
+    KmerIndex::rebuild(&args.output, &src, &filters, mode, args.force, &mut rep)
+        .unwrap_or_else(|e| {
+            eprintln!("error rebuilding index: {e}");
+            std::process::exit(1);
+        });
+
+    rep.print();
+    info!("rebuilt index → {}", args.output.display());
+}
diff --git a/src/obikmer/src/main.rs b/src/obikmer/src/main.rs
index c88428b..bae4cdf 100644
--- a/src/obikmer/src/main.rs
+++ b/src/obikmer/src/main.rs
@@ -20,6 +20,8 @@ enum Commands {
     Index(cmd::index::IndexArgs),
     /// Merge multiple built indexes into one
     Merge(cmd::merge::MergeArgs),
+    /// Filter and compact an existing index into a new single-layer index
+    Rebuild(cmd::rebuild::RebuildArgs),
     /// Dump all indexed kmers as CSV (kmer + per-genome counts or presence)
     Dump(cmd::dump::DumpArgs),
     /// Compute pairwise distance matrix between genomes; optionally build NJ/UPGMA trees
@@ -51,6 +53,7 @@ fn main() {
         Commands::Index(args)     => cmd::index::run(args),
         Commands::Merge(args)     => cmd::merge::run(args),
         Commands::Dump(args)      => cmd::dump::run(args),
+        Commands::Rebuild(args)   => cmd::rebuild::run(args),
         Commands::Distance(args)  => cmd::distance::run(args),
         Commands::Unitig(args)    => cmd::unitig::run(args),
     }
diff --git a/src/obikpartitionner/src/filter.rs b/src/obikpartitionner/src/filter.rs
new file mode 100644
index 0000000..f35a3e8
--- /dev/null
+++ b/src/obikpartitionner/src/filter.rs
@@ -0,0 +1,87 @@
+/// Trait for kmer row filters used in the rebuild command.
+///
+/// `row` contains raw per-genome counts (or 0/1 for presence/absence data).
+/// `n_genomes` equals `row.len()`.
+pub trait KmerFilter: Send + Sync {
+    fn passes(&self, row: &[u32], n_genomes: usize) -> bool;
+}
+
+// ── Quorum filters ─────────────────────────────────────────────────────────────
+
+fn present_count(row: &[u32], threshold: u32) -> usize {
+    row.iter().filter(|&&v| v > threshold).count()
+}
+
+/// At least `frac` fraction of genomes contain this kmer (count > `threshold`).
+pub struct MinGenomeFraction {
+    pub frac: f64,
+    pub threshold: u32,
+}
+
+impl KmerFilter for MinGenomeFraction {
+    fn passes(&self, row: &[u32], n_genomes: usize) -> bool {
+        let p = present_count(row, self.threshold);
+        p as f64 / n_genomes as f64 >= self.frac
+    }
+}
+
+/// At most `frac` fraction of genomes contain this kmer (count > `threshold`).
+pub struct MaxGenomeFraction {
+    pub frac: f64,
+    pub threshold: u32,
+}
+
+impl KmerFilter for MaxGenomeFraction {
+    fn passes(&self, row: &[u32], n_genomes: usize) -> bool {
+        let p = present_count(row, self.threshold);
+        p as f64 / n_genomes as f64 <= self.frac
+    }
+}
+
+/// At least `count` genomes contain this kmer (count > `threshold`).
+pub struct MinGenomeCount {
+    pub count: usize,
+    pub threshold: u32,
+}
+
+impl KmerFilter for MinGenomeCount {
+    fn passes(&self, row: &[u32], _n_genomes: usize) -> bool {
+        present_count(row, self.threshold) >= self.count
+    }
+}
+
+/// At most `count` genomes contain this kmer (count > `threshold`).
+pub struct MaxGenomeCount {
+    pub count: usize,
+    pub threshold: u32,
+}
+
+impl KmerFilter for MaxGenomeCount {
+    fn passes(&self, row: &[u32], _n_genomes: usize) -> bool {
+        present_count(row, self.threshold) <= self.count
+    }
+}
+
+// ── Total-count filters (count indexes only) ───────────────────────────────────
+
+/// Sum of counts across all genomes >= `total`.
+pub struct MinTotalCount {
+    pub total: u32,
+}
+
+impl KmerFilter for MinTotalCount {
+    fn passes(&self, row: &[u32], _n_genomes: usize) -> bool {
+        row.iter().sum::<u32>() >= self.total
+    }
+}
+
+/// Sum of counts across all genomes <= `total`.
+pub struct MaxTotalCount {
+    pub total: u32,
+}
+
+impl KmerFilter for MaxTotalCount {
+    fn passes(&self, row: &[u32], _n_genomes: usize) -> bool {
+        row.iter().sum::<u32>() <= self.total
+    }
+}
diff --git a/src/obikpartitionner/src/lib.rs b/src/obikpartitionner/src/lib.rs
index 4b03fce..48d72c1 100644
--- a/src/obikpartitionner/src/lib.rs
+++ b/src/obikpartitionner/src/lib.rs
@@ -1,9 +1,12 @@
+pub mod filter;
 mod distance;
 mod dump_layer;
 mod index_layer;
 mod kmer_sort;
 mod merge_layer;
 mod partition;
+mod rebuild_layer;
 
+pub use filter::KmerFilter;
 pub use merge_layer::MergeMode;
 pub use partition::{KmerPartition, KmerSpectrum, PARTITIONS_SUBDIR};
diff --git a/src/obikpartitionner/src/merge_layer.rs b/src/obikpartitionner/src/merge_layer.rs
index c933966..21785d0 100644
--- a/src/obikpartitionner/src/merge_layer.rs
+++ b/src/obikpartitionner/src/merge_layer.rs
@@ -44,7 +44,7 @@ impl ColBuilder {
 
 // ── SrcLayerData — opened source matrix for pass-2 lookup ─────────────────────
 
-enum SrcLayerData {
+pub(crate) enum SrcLayerData {
     /// Pure set-membership layer (no data matrix): every kmer is present in all genomes.
     SetMembership,
     Presence(MphfLayer, PersistentBitMatrix),
@@ -52,7 +52,7 @@ enum SrcLayerData {
 }
 
 impl SrcLayerData {
-    fn open(layer_dir: &Path, mode: MergeMode) -> SKResult<Self> {
+    pub(crate) fn open(layer_dir: &Path, mode: MergeMode) -> SKResult<Self> {
         let presence_dir = layer_dir.join("presence");
         let counts_dir   = layer_dir.join("counts");
         match mode {
@@ -83,7 +83,7 @@ impl SrcLayerData {
     }
 
     /// Return one value per source genome for `kmer`.
-    fn lookup(&self, kmer: CanonicalKmer, n_genomes: usize) -> Vec<u32> {
+    pub(crate) fn lookup(&self, kmer: CanonicalKmer, n_genomes: usize) -> Vec<u32> {
         match self {
             SrcLayerData::SetMembership => vec![1u32; n_genomes],
             SrcLayerData::Presence(mphf, mat) => {
diff --git a/src/obikpartitionner/src/rebuild_layer.rs b/src/obikpartitionner/src/rebuild_layer.rs
new file mode 100644
index 0000000..fa581f9
--- /dev/null
+++ b/src/obikpartitionner/src/rebuild_layer.rs
@@ -0,0 +1,205 @@
+use std::fs;
+use std::io;
+use std::path::{Path, PathBuf};
+
+use obicompactvec::{PersistentBitMatrixBuilder,
+                    PersistentBitVecBuilder,
+                    PersistentCompactIntMatrixBuilder,
+                    PersistentCompactIntVecBuilder};
+use obidebruinj::GraphDeBruijn;
+use obiskio::{SKError, SKResult, UnitigFileReader};
+use obilayeredmap::{Layer, MphfLayer, OLMError};
+use obilayeredmap::meta::PartitionMeta;
+
+use crate::filter::KmerFilter;
+use crate::merge_layer::{MergeMode, SrcLayerData};
+use crate::partition::KmerPartition;
+
+const INDEX_SUBDIR: &str = "index";
+
+fn olm_to_sk(e: OLMError) -> SKError {
+    match e {
+        OLMError::Io(e) => SKError::Io(e),
+        other => SKError::InvalidData { context: "rebuild", detail: other.to_string() },
+    }
+}
+
+fn col_path_bit(dir: &Path, col: usize) -> PathBuf {
+    dir.join(format!("col_{col:06}.pbiv"))
+}
+
+fn col_path_int(dir: &Path, col: usize) -> PathBuf {
+    dir.join(format!("col_{col:06}.pciv"))
+}
+
+fn write_matrix_meta(dir: &Path, n: usize, n_cols: usize) -> io::Result<()> {
+    fs::write(dir.join("meta.json"), format!("{{\"n\":{n},\"n_cols\":{n_cols}}}\n"))
+}
+
+// ── ColBuilder ────────────────────────────────────────────────────────────────
+
+enum ColBuilder {
+    Bit(PersistentBitVecBuilder),
+    Int(PersistentCompactIntVecBuilder),
+}
+
+impl ColBuilder {
+    fn set_val(&mut self, slot: usize, value: u32) {
+        match self {
+            ColBuilder::Bit(b) => b.set(slot, value > 0),
+            ColBuilder::Int(b) => b.set(slot, value),
+        }
+    }
+
+    fn close(self) -> SKResult<()> {
+        match self {
+            ColBuilder::Bit(b)  => b.close().map_err(SKError::Io),
+            ColBuilder::Int(b)  => b.close().map_err(SKError::Io),
+        }
+    }
+}
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+fn load_meta(dir: &Path) -> SKResult<PartitionMeta> {
+    match PartitionMeta::load(dir) {
+        Ok(m) => Ok(m),
+        Err(e) if matches!(e, OLMError::Io(ref io_e) if io_e.kind() == std::io::ErrorKind::NotFound) => {
+            let mut n = 0usize;
+            while dir.join(format!("layer_{n}")).exists() { n += 1; }
+            let m = PartitionMeta { n_layers: n };
+            m.save(dir).map_err(olm_to_sk)?;
+            Ok(m)
+        }
+        Err(e) => Err(olm_to_sk(e)),
+    }
+}
+
+fn passes_all(filters: &[Box<dyn KmerFilter>], row: &[u32], n_genomes: usize) -> bool {
+    filters.iter().all(|f| f.passes(row, n_genomes))
+}
+
+// ── KmerPartition::rebuild_partition ─────────────────────────────────────────
+
+impl KmerPartition {
+    /// Rebuild partition `i` from `src` into `self` (an empty destination partition).
+    ///
+    /// Only k-mers whose per-genome row passes all `filters` are written.
+    /// The output is a single-layer index — regardless of how many layers the
+    /// source has.
+    ///
+    /// `n_genomes` is the number of genome columns in the source (and destination).
+    pub fn rebuild_partition(
+        &self,
+        src: &KmerPartition,
+        i: usize,
+        filters: &[Box<dyn KmerFilter>],
+        mode: MergeMode,
+        n_genomes: usize,
+    ) -> SKResult<()> {
+        let src_index_dir = src.part_dir(i).join(INDEX_SUBDIR);
+        if !src_index_dir.exists() {
+            return Ok(());
+        }
+
+        let src_meta = load_meta(&src_index_dir)?;
+        if src_meta.n_layers == 0 {
+            return Ok(());
+        }
+
+        // ── Pass 1: collect filtered kmers into de Bruijn graph ───────────────
+        let mut g = GraphDeBruijn::new();
+
+        for l in 0..src_meta.n_layers {
+            let src_layer_dir = src_index_dir.join(format!("layer_{l}"));
+            let unitigs_path = src_layer_dir.join("unitigs.bin");
+            if !unitigs_path.exists() { continue; }
+
+            let reader = UnitigFileReader::open(&unitigs_path)?;
+            let src_data = SrcLayerData::open(&src_layer_dir, mode)?;
+
+            for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
+                let row = src_data.lookup(kmer, n_genomes);
+                if passes_all(filters, &row, n_genomes) {
+                    g.push(kmer);
+                }
+            }
+        }
+
+        if g.len() == 0 {
+            return Ok(());
+        }
+
+        let n_new = g.len();
+        g.compute_degrees();
+
+        // ── Build MPHF in dst layer_0 ─────────────────────────────────────────
+        let dst_index_dir = self.part_dir(i).join(INDEX_SUBDIR);
+        let dst_layer_dir = dst_index_dir.join("layer_0");
+        fs::create_dir_all(&dst_layer_dir)?;
+
+        let mut uw = Layer::<()>::unitig_writer(&dst_layer_dir).map_err(olm_to_sk)?;
+        for unitig in g.iter_unitig() {
+            uw.write(&unitig)?;
+        }
+        uw.close()?;
+        drop(g);
+
+        Layer::<()>::build(&dst_layer_dir).map_err(olm_to_sk)?;
+        let dst_mphf = MphfLayer::open(&dst_layer_dir).map_err(olm_to_sk)?;
+
+        // ── Prepare matrix builders (one column per genome) ───────────────────
+        let data_dir = match mode {
+            MergeMode::Presence => dst_layer_dir.join("presence"),
+            MergeMode::Count    => dst_layer_dir.join("counts"),
+        };
+        fs::create_dir_all(&data_dir)?;
+
+        let mut builders: Vec<ColBuilder> = match mode {
+            MergeMode::Presence => {
+                PersistentBitMatrixBuilder::new(n_new, &data_dir)
+                    .map_err(SKError::Io)?.close().map_err(SKError::Io)?;
+                (0..n_genomes).map(|g| -> SKResult<ColBuilder> {
+                    let b = PersistentBitVecBuilder::new(n_new, &col_path_bit(&data_dir, g))?;
+                    Ok(ColBuilder::Bit(b))
+                }).collect::<SKResult<_>>()?
+            }
+            MergeMode::Count => {
+                PersistentCompactIntMatrixBuilder::new(n_new, &data_dir)
+                    .map_err(SKError::Io)?.close().map_err(SKError::Io)?;
+                (0..n_genomes).map(|g| -> SKResult<ColBuilder> {
+                    let b = PersistentCompactIntVecBuilder::new(n_new, &col_path_int(&data_dir, g))?;
+                    Ok(ColBuilder::Int(b))
+                }).collect::<SKResult<_>>()?
+            }
+        };
+
+        // ── Pass 2: fill builders ─────────────────────────────────────────────
+        for l in 0..src_meta.n_layers {
+            let src_layer_dir = src_index_dir.join(format!("layer_{l}"));
+            let unitigs_path = src_layer_dir.join("unitigs.bin");
+            if !unitigs_path.exists() { continue; }
+
+            let reader = UnitigFileReader::open(&unitigs_path)?;
+            let src_data = SrcLayerData::open(&src_layer_dir, mode)?;
+
+            for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
+                let row = src_data.lookup(kmer, n_genomes);
+                if !passes_all(filters, &row, n_genomes) { continue; }
+                if let Some(slot) = dst_mphf.find(kmer) {
+                    for (col, &value) in row.iter().enumerate() {
+                        builders[col].set_val(slot, value);
+                    }
+                }
+            }
+        }
+
+        // ── Close builders, write metadata ────────────────────────────────────
+        for b in builders { b.close()?; }
+        write_matrix_meta(&data_dir, n_new, n_genomes).map_err(SKError::Io)?;
+
+        PartitionMeta { n_layers: 1 }.save(&dst_index_dir).map_err(olm_to_sk)?;
+
+        Ok(())
+    }
+}