diff --git a/pkgs/by-name/li/libmamba/package.nix b/pkgs/by-name/li/libmamba/package.nix
index bd063f6cee84..3b7e461d60b4 100644
--- a/pkgs/by-name/li/libmamba/package.nix
+++ b/pkgs/by-name/li/libmamba/package.nix
@@ -1,33 +1,34 @@
 {
-  fetchFromGitHub,
-  lib,
-  stdenv,
-  cmake,
-  fmt,
-  spdlog,
-  tl-expected,
-  nlohmann_json,
-  yaml-cpp,
-  simdjson,
-  reproc,
-  libsolv,
-  curl,
-  libarchive,
-  zstd,
-  nix-update-script,
   bzip2,
+  cmake,
+  curl,
+  fetchFromGitHub,
+  fmt,
+  lib,
+  libarchive,
+  libsolv,
+  msgpack-c,
+  nix-update-script,
+  nlohmann_json,
   python3,
+  reproc,
+  simdjson,
+  spdlog,
+  stdenv,
+  tl-expected,
+  yaml-cpp,
+  zstd,
 }:
 
 stdenv.mkDerivation (finalAttrs: {
   pname = "libmamba";
-  version = "2.4.0";
+  version = "2.6.2";
 
   src = fetchFromGitHub {
     owner = "mamba-org";
     repo = "mamba";
     tag = finalAttrs.version;
-    hash = "sha256-ojcAS5NYAhklACrBkmSHRPNiVLjUR/umll0vhoFnFBs=";
+    hash = "sha256-qvUo2OD+vh5oXF/ckz9vJyiQ9wpEbTrC+C4oYXOGFAU=";
   };
 
   nativeBuildInputs = [
@@ -36,25 +37,30 @@ stdenv.mkDerivation (finalAttrs: {
   ];
 
   buildInputs = [
+    bzip2
+    curl
     fmt
+    libarchive
+    libsolv
+    msgpack-c
+    nlohmann_json
+    reproc
+    simdjson
     spdlog
     tl-expected
-    nlohmann_json
     yaml-cpp
-    simdjson
-    reproc
-    libsolv
-    curl
-    libarchive
     zstd
-    bzip2
   ];
 
   cmakeFlags = [
     (lib.cmakeBool "BUILD_LIBMAMBA" true)
+    (lib.cmakeBool "BUILD_LIBMAMBA_SPDLOG" true)
     (lib.cmakeBool "BUILD_SHARED" true)
   ];
 
+  __structuredAttrs = true;
+  strictDeps = true;
+
   passthru.updateScript = nix-update-script { };
 
   meta = {
diff --git a/pkgs/by-name/ma/mamba-cpp/package.nix b/pkgs/by-name/ma/mamba-cpp/package.nix
index 344a9e9d3eef..d362aa0941da 100644
--- a/pkgs/by-name/ma/mamba-cpp/package.nix
+++ b/pkgs/by-name/ma/mamba-cpp/package.nix
@@ -1,36 +1,46 @@
 {
-  lib,
-  stdenv,
   bzip2,
-  cmake,
   cli11,
-  yaml-cpp,
+  cmake,
+  lib,
+  libmamba,
+  makeWrapper,
+  msgpack-c,
   nlohmann_json,
-  zstd,
+  python3,
   reproc,
   spdlog,
+  stdenv,
   tl-expected,
-  libmamba,
-  python3,
   versionCheckHook,
+  yaml-cpp,
+  zstd,
+  # runtime options
+  defaultEnvPath ? "~/.mamba/envs",
+  defaultPkgPath ? "~/.mamba/pkgs",
+  defaultRootPath ? "~/.mamba",
 }:
 stdenv.mkDerivation {
   pname = "mamba-cpp";
   inherit (libmamba) version src;
 
-  nativeBuildInputs = [ cmake ];
+  nativeBuildInputs = [
+    cmake
+    makeWrapper
+  ];
 
   buildInputs = [
+    bzip2
+    cli11
+    libmamba
+    msgpack-c
+    nlohmann_json
     python3
     reproc
     spdlog
-    nlohmann_json
     tl-expected
-    zstd
-    bzip2
-    cli11
     yaml-cpp
-    libmamba
+    zstd
   ];
 
   cmakeFlags = [
@@ -41,6 +51,16 @@ stdenv.mkDerivation {
 
   nativeInstallCheckInputs = [ versionCheckHook ];
 
+  postInstall = ''
+    wrapProgram $out/bin/mamba \
+      --set-default CONDA_ENVS_PATH '${defaultEnvPath}' \
+      --set-default CONDA_PKGS_DIRS '${defaultPkgPath}' \
+      --set-default MAMBA_ROOT_PREFIX '${defaultRootPath}'
+  '';
+
+  __structuredAttrs = true;
+  strictDeps = true;
+
   meta = {
     description = "Reimplementation of the conda package manager";
     homepage = "https://github.com/mamba-org/mamba";
diff --git a/pkgs/development/python-modules/conda-libmamba-solver/default.nix b/pkgs/development/python-modules/conda-libmamba-solver/default.nix
index 7220bb94f1aa..8e73b16b3c35 100644
--- a/pkgs/development/python-modules/conda-libmamba-solver/default.nix
+++ b/pkgs/development/python-modules/conda-libmamba-solver/default.nix
@@ -1,26 +1,25 @@
 {
-  lib,
+  boltons,
   buildPythonPackage,
   fetchFromGitHub,
   hatchling,
   hatch-vcs,
-  boltons,
+  lib,
   libmambapy,
   msgpack,
   requests,
   zstandard,
 }:
-buildPythonPackage rec {
+buildPythonPackage (finalAttrs: {
   pname = "conda-libmamba-solver";
-  version = "25.11.0";
+  version = "26.4.2";
   pyproject = true;
 
   src = fetchFromGitHub {
-    inherit pname version;
     owner = "conda";
     repo = "conda-libmamba-solver";
-    tag = version;
-    hash = "sha256-t4mwQ9nsduicT1sL1TQLbuCoS4r7K/GaXyBFOO+3/m8=";
+    tag = finalAttrs.version;
+    hash = "sha256-8+BIUQp2tg50P0UDjzBvywg8/mDelDYMtp/ejEcMH20=";
   };
 
   build-system = [
@@ -47,4 +46,4 @@ buildPythonPackage rec {
     license = lib.licenses.bsd3;
     maintainers = [ lib.maintainers.ericthemagician ];
   };
-}
+})
diff --git a/pkgs/development/python-modules/conda/default.nix b/pkgs/development/python-modules/conda/default.nix
index dce5a4cf2458..0173ce5552e5 100644
--- a/pkgs/development/python-modules/conda/default.nix
+++ b/pkgs/development/python-modules/conda/default.nix
@@ -28,7 +28,7 @@
 buildPythonPackage rec {
   __structuredAttrs = true;
   pname = "conda";
-  version = "26.1.0";
+  version = "26.5.0";
   pyproject = true;
 
   src = fetchFromGitHub {
@@ -36,7 +36,7 @@ buildPythonPackage rec {
     owner = "conda";
     repo = "conda";
     tag = version;
-    hash = "sha256-u3xxaSNfPocAjzvzEhKNijsa2lR4xiMSpWHP4MTnBzQ=";
+    hash = "sha256-x6p9CaityAO8NYiKLGUbu3Lk5C/mVmMmdqP4OpfSkNs=";
   };
 
   build-system = [
@@ -44,6 +44,8 @@ buildPythonPackage rec {
     hatch-vcs
   ];
 
+  pythonRelaxDeps = [ "ruamel-yaml" ];
+
   dependencies = [
     archspec
     conda-libmamba-solver
diff --git a/pkgs/development/python-modules/libmambapy/default.nix b/pkgs/development/python-modules/libmambapy/default.nix
index 84eada8537bb..907fb0ae5116 100644
--- a/pkgs/development/python-modules/libmambapy/default.nix
+++ b/pkgs/development/python-modules/libmambapy/default.nix
@@ -1,22 +1,23 @@
 {
-  lib,
-  python,
-  buildPythonPackage,
+  bzip2,
   cmake,
-  ninja,
-  libmamba,
-  pybind11,
-  scikit-build-core,
+  curl,
+  buildPythonPackage,
   fmt,
+  lib,
+  libmamba,
+  libsolv,
+  msgpack-c,
+  ninja,
+  nlohmann_json,
+  pybind11,
+  python,
+  reproc,
+  scikit-build-core,
   spdlog,
   tl-expected,
-  nlohmann_json,
   yaml-cpp,
-  reproc,
-  libsolv,
-  curl,
   zstd,
-  bzip2,
 }:
 
 buildPythonPackage rec {
@@ -38,16 +39,17 @@ buildPythonPackage rec {
 
   buildInputs = [
     (libmamba.override { python3 = python; })
-    curl
-    zstd
     bzip2
-    spdlog
+    curl
     fmt
-    tl-expected
-    nlohmann_json
-    yaml-cpp
-    reproc
     libsolv
+    msgpack-c
+    nlohmann_json
+    reproc
+    spdlog
+    tl-expected
+    yaml-cpp
+    zstd
   ];
 
   pythonImportsCheck = [