diff --git a/Cargo.lock b/Cargo.lock
index 1b4a6f10fc5..95ca7dc8c42 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2635,6 +2635,28 @@ dependencies = [
  "whoami",
 ]
 
+[[package]]
+name = "jj-core"
+version = "0.44.0"
+dependencies = [
+ "assert_matches",
+ "bstr",
+ "criterion",
+ "either",
+ "eyre",
+ "futures 0.3.33",
+ "globset",
+ "hashbrown 0.17.1",
+ "indexmap",
+ "insta",
+ "itertools 0.15.0",
+ "maplit",
+ "pollster",
+ "regex",
+ "smallvec",
+ "thiserror 2.0.19",
+]
+
 [[package]]
 name = "jj-lib"
 version = "0.44.0"
@@ -2645,7 +2667,6 @@ dependencies = [
  "bstr",
  "chrono",
  "clru",
- "criterion",
  "digest 0.10.7",
  "dunce",
  "either",
@@ -2655,12 +2676,12 @@ dependencies = [
  "gix",
  "gix-ignore",
  "globset",
- "hashbrown 0.17.1",
  "indexmap",
  "indoc",
  "insta",
  "interim",
  "itertools 0.15.0",
+ "jj-core",
  "jj-lib-proc-macros",
  "maplit",
  "memchr",
diff --git a/Cargo.toml b/Cargo.toml
index ad90a9fba29..1641b3e79dc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,14 @@ cargo-features = []
 
 [workspace]
 resolver = "3"
-members = ["cli", "lib", "lib/gen-protos", "lib/proc-macros", "lib/testutils"]
+members = [
+    "cli",
+    "core",
+    "lib",
+    "lib/gen-protos",
+    "lib/proc-macros",
+    "lib/testutils",
+]
 
 [workspace.package]
 version = "0.44.0"
@@ -139,6 +146,7 @@ winreg = "0.56"
 
 # put all inter-workspace libraries, i.e. those that use 'path = ...' here in
 # their own (alphabetically sorted) block
+jj-core = { path = "core", version = "0.44.0" }
 jj-lib = { path = "lib", version = "0.44.0", default-features = false }
 jj-lib-proc-macros = { path = "lib/proc-macros", version = "0.44.0" }
 testutils = { path = "lib/testutils" }
diff --git a/core/Cargo.toml b/core/Cargo.toml
new file mode 100644
index 00000000000..c70da7b8c97
--- /dev/null
+++ b/core/Cargo.toml
@@ -0,0 +1,39 @@
+[package]
+name = "jj-core"
+version.workspace = true
+license.workspace = true
+rust-version.workspace = true
+edition.workspace = true
+readme.workspace = true
+homepage.workspace = true
+repository.workspace = true
+documentation.workspace = true
+categories.workspace = true
+keywords.workspace = true
+
+[[bench]]
+name = "diff_bench"
+harness = false
+
+[dependencies]
+bstr = { workspace = true }
+either = { workspace = true }
+futures = { workspace = true }
+globset = { workspace = true }
+hashbrown = { workspace = true }
+indexmap = { workspace = true }
+itertools = { workspace = true }
+regex = { workspace = true }
+smallvec = { workspace = true }
+thiserror = { workspace = true }
+
+[dev-dependencies]
+assert_matches = { workspace = true }
+criterion = { workspace = true }
+eyre = { workspace = true }
+insta = { workspace = true }
+maplit = { workspace = true }
+pollster = { workspace = true }
+
+[lints]
+workspace = true
diff --git a/lib/benches/diff_bench.rs b/core/benches/diff_bench.rs
similarity index 99%
rename from lib/benches/diff_bench.rs
rename to core/benches/diff_bench.rs
index c1c8bf4b4ed..0a104331cc1 100644
--- a/lib/benches/diff_bench.rs
+++ b/core/benches/diff_bench.rs
@@ -2,7 +2,7 @@ use criterion::BenchmarkId;
 use criterion::Criterion;
 use criterion::criterion_group;
 use criterion::criterion_main;
-use jj_lib::diff;
+use jj_core::diff;
 
 fn unchanged_lines(count: usize) -> (String, String) {
     let mut lines = vec![];
diff --git a/lib/src/dag_walk.rs b/core/src/dag_walk.rs
similarity index 100%
rename from lib/src/dag_walk.rs
rename to core/src/dag_walk.rs
diff --git a/lib/src/dag_walk_async.rs b/core/src/dag_walk_async.rs
similarity index 100%
rename from lib/src/dag_walk_async.rs
rename to core/src/dag_walk_async.rs
diff --git a/lib/src/diff.rs b/core/src/diff.rs
similarity index 100%
rename from lib/src/diff.rs
rename to core/src/diff.rs
diff --git a/lib/src/hex_util.rs b/core/src/hex_util.rs
similarity index 100%
rename from lib/src/hex_util.rs
rename to core/src/hex_util.rs
diff --git a/core/src/lib.rs b/core/src/lib.rs
new file mode 100644
index 00000000000..ade500f8555
--- /dev/null
+++ b/core/src/lib.rs
@@ -0,0 +1,32 @@
+// Copyright 2026 The Jujutsu Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! The core library powering the Jujutsu Version Control System. It contains
+//! all "base" types such as `Commit` and the `Backend` trait.
+
+#![warn(missing_docs)]
+#![forbid(unsafe_code)]
+#![deny(unused_must_use)]
+
+pub mod dag_walk;
+pub mod dag_walk_async;
+pub mod diff;
+pub mod hex_util;
+pub mod str_util;
+
+#[cfg(test)]
+mod tests {
+    // Copied from `testutils::TestResult` to remove dependency cycle.
+    pub type TestResult<T = ()> = eyre::Result<T>;
+}
diff --git a/lib/src/str_util.rs b/core/src/str_util.rs
similarity index 100%
rename from lib/src/str_util.rs
rename to core/src/str_util.rs
diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index 152fc1700c5..ed2b49765f1 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -14,7 +14,6 @@ readme = { workspace = true }
 
 include = [
     "/LICENSE",
-    "/benches/",
     "/src/",
     "/tests/",
     "!*.pending-snap",
@@ -25,10 +24,6 @@ include = [
 [[test]]
 name = "runner"
 
-[[bench]]
-name = "diff_bench"
-harness = false
-
 [dependencies]
 async-trait = { workspace = true }
 blake2 = { workspace = true }
@@ -43,10 +38,10 @@ futures = { workspace = true }
 gix = { workspace = true, optional = true }
 gix-ignore = { workspace = true }
 globset = { workspace = true }
-hashbrown = { workspace = true }
 indexmap = { workspace = true }
 interim = { workspace = true }
 itertools = { workspace = true }
+jj-core = { workspace = true }
 jj-lib-proc-macros = { workspace = true }
 maplit = { workspace = true }
 memchr = { workspace = true }
@@ -79,7 +74,6 @@ winreg = { workspace = true }
 
 [dev-dependencies]
 assert_matches = { workspace = true }
-criterion = { workspace = true }
 eyre = { workspace = true }
 indoc = { workspace = true }
 insta = { workspace = true }
diff --git a/lib/src/lib.rs b/lib/src/lib.rs
index 5ed1381c8f0..34fd1479501 100644
--- a/lib/src/lib.rs
+++ b/lib/src/lib.rs
@@ -40,12 +40,12 @@ pub mod conflict_labels;
 pub mod conflicts;
 pub mod converge;
 pub mod copies;
-pub mod dag_walk;
-pub mod dag_walk_async;
+pub use jj_core::dag_walk;
+pub use jj_core::dag_walk_async;
 pub mod default_backend_factories;
 pub mod default_index;
 pub mod default_submodule_store;
-pub mod diff;
+pub use jj_core::diff;
 pub mod diff_presentation;
 pub mod dsl_util;
 pub(crate) mod eol;
@@ -68,7 +68,7 @@ pub mod gitignore;
 pub mod gpg_signing;
 pub mod graph;
 pub mod graph_dominators;
-pub mod hex_util;
+pub use jj_core::hex_util;
 pub mod id_prefix;
 pub mod index;
 pub mod iter_util;
@@ -107,7 +107,7 @@ pub mod simple_op_store;
 pub mod ssh_signing;
 pub mod stacked_table;
 pub mod store;
-pub mod str_util;
+pub use jj_core::str_util;
 pub mod submodule_store;
 #[cfg(feature = "testing")]
 pub mod test_signing_backend;