diff --git a/docmd/implementation/filtering.md b/docmd/implementation/filtering.md
index 795d8fd..4dfab31 100644
--- a/docmd/implementation/filtering.md
+++ b/docmd/implementation/filtering.md
@@ -1,12 +1,12 @@
 # Kmer filtering and ingroup/outgroup predicates
 
-The `rebuild`, `dump`, and `unitig` commands share the same filtering system,
+The `filter`, `dump`, and `unitig` commands share the same filtering system,
 implemented as a shared `FilterArgs` clap argument group embedded in each command
 via `#[command(flatten)]`. Filters select k-mers based on per-genome quorum
 counts, optionally restricted to **ingroup** and **outgroup** genome sets derived
 from genome metadata. All rules described here apply identically to all three commands.
 
-`rebuild` additionally accepts `--min-total-count` / `--max-total-count` filters
+`filter` additionally accepts `--min-total-count` / `--max-total-count` filters
 that operate on the sum of counts across all genomes.
 
 ## Predicate syntax
@@ -93,8 +93,8 @@ For each genome:
 | `--max-outgroup-count N` | outgroup | k-mer present in at most N outgroup genomes |
 | `--min-outgroup-frac F` | outgroup | k-mer present in at least fraction F of outgroup genomes |
 | `--max-outgroup-frac F` | outgroup | k-mer present in at most fraction F of outgroup genomes |
-| `--min-total-count N` | all genomes | sum of per-genome counts ≥ N (`rebuild` only) |
-| `--max-total-count N` | all genomes | sum of per-genome counts ≤ N (`rebuild` only) |
+| `--min-total-count N` | all genomes | sum of per-genome counts ≥ N (`filter` only) |
+| `--max-total-count N` | all genomes | sum of per-genome counts ≤ N (`filter` only) |
 | `--presence-threshold N` | all | per-genome count > N to be considered "present" (default 0) |
 
 **Conditional defaults** — the defaults for `--min-frac` and `--max-outgroup-count` depend on two conditions:
@@ -169,7 +169,7 @@ Keep k-mers specific to *Betula nana* — present in at least 2 *B. nana* genome
 and absent from every other genome in the index:
 
 ```sh
-obikmer rebuild src --output dst \
+obikmer filter src --output dst \
   --ingroup  "species=Betula_nana" \
   --outgroup "*" \
   --min-count 2 \
@@ -180,7 +180,7 @@ Keep k-mers found in at least 2 *Betula nana* genomes and absent from all
 other *Betula*:
 
 ```sh
-obikmer rebuild src --output dst \
+obikmer filter src --output dst \
   --ingroup  "species=Betula_nana" \
   --outgroup "genus=Betula" \
   --min-count 2 \
@@ -191,7 +191,7 @@ Use taxonomic paths — keep k-mers present in ≥ 50 % of the *Betula* clade
 and in fewer than 10 % of everything outside *Betulaceae*:
 
 ```sh
-obikmer rebuild src --output dst \
+obikmer filter src --output dst \
   --ingroup  "taxon~/Betulaceae/Betula" \
   --outgroup "taxon!~/Betulaceae" \
   --min-frac 0.5 \
@@ -201,7 +201,7 @@ obikmer rebuild src --output dst \
 Multiple outgroup predicates (OR): exclude k-mers present in *Alnus* or *Carpinus*:
 
 ```sh
-obikmer rebuild src --output dst \
+obikmer filter src --output dst \
   --ingroup  "genus=Betula" \
   --outgroup "genus=Alnus" \
   --outgroup "genus=Carpinus" \
@@ -244,7 +244,7 @@ obikmer dump myindex --head 20 --ingroup "species=Betula_nana" --min-count 1
 ### `distance --presence-threshold N`
 
 When computing Jaccard distance on a **count index**, a k-mer is considered present in a genome if its count is ≥ N (default 1).
-This option is independent of the `--presence-threshold` used in `rebuild`/`query` filtering.
+This option is independent of the `--presence-threshold` used in filtering.
 
 ```sh
 # Jaccard treating kmers with count ≥ 2 as present
@@ -262,11 +262,11 @@ This parameter has no effect on presence/absence indexes (where values are alrea
   lookup and counter.
 
 - **`obikmer::cmd::predicate::FilterArgs`** — shared `clap` argument group
-  embedded via `#[command(flatten)]` in `RebuildArgs`, `DumpArgs`, and
+  embedded via `#[command(flatten)]` in `FilterArgs`, `DumpArgs`, and
   `UnitigArgs`. `FilterArgs::build_filters()` returns a ready-to-use filter
   list.
 
 - **`obikpartitionner::KmerPartition::iter_partition_kmers`** — accepts
   `filters: &[Box<dyn KmerFilter>]` and applies them per-kmer before invoking
-  the callback. `rebuild`, `dump`, and `unitig` all go through this single
+  the callback. `filter`, `dump`, and `unitig` all go through this single
   entry point.
diff --git a/docmd/implementation/select.md b/docmd/implementation/select.md
index 8fbb022..d78a3fd 100644
--- a/docmd/implementation/select.md
+++ b/docmd/implementation/select.md
@@ -56,8 +56,8 @@ first, then renames atomically, so an interrupted run leaves the index intact.
 --group <name>:<pred>
 ```
 
-Defines a named group of genomes using the same predicate syntax as
-`filter`/`rebuild`. Repeatable; a genome can belong to several groups.
+Defines a named group of genomes using the same predicate syntax as `filter`.
+Repeatable; a genome can belong to several groups.
 
 ```sh
 --group "pub:species=Betula_pubescens"
diff --git a/docmd/index.md b/docmd/index.md
index e2d96ca..9f6d650 100644
--- a/docmd/index.md
+++ b/docmd/index.md
@@ -9,7 +9,7 @@
 | `superkmer` | Extract super-kmers from a sequence file and write to stdout |
 | `index`     | Build a complete genome index (scatter → dereplicate → count → layered MPHF) |
 | `merge`     | Merge multiple built indexes into one |
-| `rebuild` / `filter` | Filter and compact an existing index into a new single-layer index; supports the shared [kmer filtering](implementation/filtering.md) system (`filter` is an alias for `rebuild`) |
+| `filter` | Apply row-level selection (σ) to an index: retain only k-mers matching the ingroup/outgroup predicates. Output is a new single-layer index — compaction is a consequence, not the goal. Supports the shared [kmer filtering](implementation/filtering.md) system |
 | `query`     | Query an index with sequences and annotate matches |
 | `dump`      | Dump all indexed k-mers as CSV (kmer + per-genome counts or presence); supports the shared [kmer filtering](implementation/filtering.md) system; `--head N` limits output to the first N k-mers |
 | `annotate`  | Add or update genome metadata from a CSV file; or dump metadata as CSV |
diff --git a/src/obikmer/src/cmd/rebuild.rs b/src/obikmer/src/cmd/filter.rs
similarity index 84%
rename from src/obikmer/src/cmd/rebuild.rs
rename to src/obikmer/src/cmd/filter.rs
index 594d5f4..993f80a 100644
--- a/src/obikmer/src/cmd/rebuild.rs
+++ b/src/obikmer/src/cmd/filter.rs
@@ -6,10 +6,10 @@ use obikpartitionner::filter::{MaxTotalCount, MinTotalCount};
 use obisys::Reporter;
 use tracing::info;
 
-use super::predicate::FilterArgs;
+use super::predicate::FilterArgs as KmerFilterArgs;
 
 #[derive(Args)]
-pub struct RebuildArgs {
+pub struct FilterArgs {
     /// Source index directory
     pub source: PathBuf,
 
@@ -18,7 +18,7 @@ pub struct RebuildArgs {
     pub output: PathBuf,
 
     #[command(flatten)]
-    pub filter: FilterArgs,
+    pub filter: KmerFilterArgs,
 
     /// Minimum total count across all genomes (count index only)
     #[arg(long)]
@@ -37,7 +37,7 @@ pub struct RebuildArgs {
     pub force: bool,
 }
 
-pub fn run(args: RebuildArgs) {
+pub fn run(args: FilterArgs) {
     let src = KmerIndex::open(&args.source).unwrap_or_else(|e| {
         eprintln!("error opening source index: {e}");
         std::process::exit(1);
@@ -50,7 +50,7 @@ pub fn run(args: RebuildArgs) {
     };
 
     info!(
-        "rebuild: {} genome(s), mode={:?}, source={}",
+        "filter: {} genome(s), mode={:?}, source={}",
         &src.meta().genomes.len(), mode, args.source.display()
     );
 
@@ -66,10 +66,10 @@ pub fn run(args: RebuildArgs) {
     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}");
+            eprintln!("error filtering index: {e}");
             std::process::exit(1);
         });
 
     rep.print();
-    info!("rebuilt index → {}", args.output.display());
+    info!("filtered index → {}", args.output.display());
 }
diff --git a/src/obikmer/src/cmd/mod.rs b/src/obikmer/src/cmd/mod.rs
index 1c1c0a6..eba674b 100644
--- a/src/obikmer/src/cmd/mod.rs
+++ b/src/obikmer/src/cmd/mod.rs
@@ -1,4 +1,5 @@
 pub mod annotate;
+pub mod filter;
 pub mod pack;
 pub(crate) mod predicate;
 pub mod select;
@@ -9,7 +10,6 @@ pub mod estimate;
 pub mod index;
 pub mod merge;
 pub mod query;
-pub mod rebuild;
 pub mod reindex;
 pub mod superkmer;
 pub mod unitig;
diff --git a/src/obikmer/src/main.rs b/src/obikmer/src/main.rs
index 224dd92..fdcf69c 100644
--- a/src/obikmer/src/main.rs
+++ b/src/obikmer/src/main.rs
@@ -20,10 +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),
-    /// Alias for rebuild
-    Filter(cmd::rebuild::RebuildArgs),
+    /// Apply row-level selection (σ) to an index: retain only k-mers matching the predicates
+    Filter(cmd::filter::FilterArgs),
     /// Project and/or aggregate genome columns into a new or in-place index
     Select(cmd::select::SelectArgs),
     /// Query an index with sequences and annotate matches
@@ -69,8 +67,7 @@ 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::Filter(args)    => cmd::rebuild::run(args),
+        Commands::Filter(args)    => cmd::filter::run(args),
         Commands::Select(args)    => cmd::select::run(args),
         Commands::Query(args)     => cmd::query::run(args),
         Commands::Annotate(args)  => cmd::annotate::run(args),