diff --git a/.changeset/floppy-brooms-cheat.md b/.changeset/floppy-brooms-cheat.md
new file mode 100644
index 00000000000..735516dd1fb
--- /dev/null
+++ b/.changeset/floppy-brooms-cheat.md
@@ -0,0 +1,5 @@
+---
+"hardhat": patch
+---
+
+Fix package manager detection
diff --git a/v-next/hardhat/src/internal/cli/init/init.ts b/v-next/hardhat/src/internal/cli/init/init.ts
index d8a10549737..0b2f092ef76 100644
--- a/v-next/hardhat/src/internal/cli/init/init.ts
+++ b/v-next/hardhat/src/internal/cli/init/init.ts
@@ -327,7 +327,7 @@ export async function validatePackageJson(
     await writeJsonFile(absolutePathToPackageJson, packageJson);
   }
 
-  const packageManager = await getPackageManager(workspace);
+  const packageManager = getPackageManager();
 
   // We know this works with npm, pnpm, but not with yarn. If, so we use
   // pnpm or npm exclusively.
@@ -491,7 +491,7 @@ export async function installProjectDependencies(
     pathToWorkspacePackageJson,
   );
 
-  const packageManager = await getPackageManager(workspace);
+  const packageManager = getPackageManager();
 
   // Find the template dev dependencies that are not already installed
   const templateDependencies = template.packageJson.devDependencies ?? {};
diff --git a/v-next/hardhat/src/internal/cli/init/package-manager.ts b/v-next/hardhat/src/internal/cli/init/package-manager.ts
index b0ee61696da..75c7c6702aa 100644
--- a/v-next/hardhat/src/internal/cli/init/package-manager.ts
+++ b/v-next/hardhat/src/internal/cli/init/package-manager.ts
@@ -1,35 +1,98 @@
 import { execSync } from "node:child_process";
-import path from "node:path";
 
-import { exists } from "@nomicfoundation/hardhat-utils/fs";
 import semver from "semver";
 
-type PackageManager = "npm" | "yarn" | "pnpm";
+type PackageManager = "npm" | "yarn" | "pnpm" | "bun" | "deno";
 
 /**
- * getPackageManager returns the name of the package manager used in the workspace.
- * It determines this by checking the presence of package manager specific lock files.
+ * getPackageManager returns the name of the package manager used to run Hardhat
  *
- * @param workspace The path to the workspace where the package manager should be checked.
- * @returns The name of the package manager used in the workspace.
+ * This logic is based on the env variable `npm_config_user_agent`, which is set
+ * by all major package manager, both when running a package that has been
+ * installed, and when it hasn't.
+ *
+ * Here's how to reproduce it, with the value of the env var:
+ *
+ * npm:
+ *
+ *   uninstalled: npx -y print-environment
+ *     "npm/11.6.1 node/v24.10.0 linux arm64 workspaces/false"
+ *
+ *   installed: npm init -y && npm i print-environment && npx print-environment
+ *     "npm/11.6.1 node/v24.10.0 linux arm64 workspaces/false"
+ *
+ *
+ * pnpm:
+ *
+ *   uninstalled: pnpm dlx print-environment
+ *     "pnpm/10.18.3 npm/? node/v24.10.0 linux arm64"
+ *
+ *   installed: pnpm init && pnpm add print-environment && pnpm print-environment
+ *     "pnpm/10.18.3 npm/? node/v24.10.0 linux arm64"
+ *
+ *
+ * yarn classic:
+ *   uninstalled: unsupported
+ *
+ *   installed: yarn init -y && yarn add print-environment && yarn print-environment
+ *     "yarn/1.22.22 npm/? node/v24.10.0 linux arm64"
+ *
+ * yarn berry:
+ *
+ *   uninstalled: yarn set version berry && yarn dlx print-environment
+ *     "yarn/4.10.3 npm/? node/v24.10.0 linux arm64"
+ *
+ *   installed: yarn set version berry && yarn add print-environment && yarn print-environment
+ *     "yarn/4.10.3 npm/? node/v24.10.0 linux arm64"
+ *
+ * bun:
+ *
+ *   uninstalled: bunx print-environment
+ *     "bun/1.3.1 npm/? node/v24.3.0 linux arm64"
+ *
+ *   installed: bun init -y && bun add print-environment && bun print-environment
+ *     "bun/1.3.1 npm/? node/v24.3.0 linux arm64"
+ *
+ * deno:
+ *
+ *   uninstalled: deno run -A npm:print-environment
+ *     "deno/2.5.6 npm/? deno/2.5.6 linux aarch64"
+ *
+ *   installed: deno init && deno add npm:print-environment && deno --allow-env print-environment
+ *     "deno/2.5.6 npm/? deno/2.5.6 linux aarch64"
+ *
+ * @returns The name of the package manager used to run hardhat.
  */
-export async function getPackageManager(
-  workspace: string,
-): Promise<PackageManager> {
-  const pathToYarnLock = path.join(workspace, "yarn.lock");
-  const pathToPnpmLock = path.join(workspace, "pnpm-lock.yaml");
+export function getPackageManager(): PackageManager {
+  const DEFAULT = "npm";
 
-  const invokedFromPnpm = (process.env.npm_config_user_agent ?? "").includes(
-    "pnpm",
-  );
+  const userAgent = process.env.npm_config_user_agent;
 
-  if (await exists(pathToYarnLock)) {
-    return "yarn";
+  if (userAgent === undefined) {
+    return DEFAULT;
   }
-  if ((await exists(pathToPnpmLock)) || invokedFromPnpm) {
-    return "pnpm";
+
+  const firstSlashIndex = userAgent.indexOf("/");
+  if (firstSlashIndex === -1) {
+    return DEFAULT;
+  }
+
+  const packageManager = userAgent.substring(0, firstSlashIndex);
+
+  switch (packageManager) {
+    case "npm":
+      return "npm";
+    case "yarn":
+      return "yarn";
+    case "pnpm":
+      return "pnpm";
+    case "bun":
+      return "bun";
+    case "deno":
+      return "deno";
+    default:
+      return DEFAULT;
   }
-  return "npm";
 }
 
 /**
@@ -49,11 +112,21 @@ export function getDevDependenciesInstallationCommand(
     npm: ["npm", "install", "--save-dev"],
     yarn: ["yarn", "add", "--dev"],
     pnpm: ["pnpm", "add", "--save-dev"],
+    deno: ["deno", "add"],
+    bun: ["bun", "add", "--dev"],
   };
   const command = packageManagerToCommand[packageManager];
   // We quote all the dependency identifiers so that they can be run on a shell
   // without semver symbols interfering with the command
-  command.push(...dependencies.map((d) => `"${d}"`));
+  command.push(
+    ...dependencies.map((d) => {
+      if (packageManager === "deno") {
+        return `"npm:${d}"`;
+      }
+
+      return `"${d}"`;
+    }),
+  );
   return command;
 }
 
@@ -118,6 +191,15 @@ export async function installsPeerDependenciesByDefault(
         }
       }
       return false;
+    case "bun":
+      // Bun has installed peer dependencies for over 2 years, so that's fine
+      // https://github.com/oven-sh/bun/releases/tag/bun-v1.0.5
+      // This can be disabled, and there's no easy way to check that, so we
+      // assume true for now
+      return true;
+    case "deno":
+      // Deno doesn't autoinstall peers
+      return false;
   }
 }
 
diff --git a/v-next/hardhat/test/internal/cli/init/package-manager.ts b/v-next/hardhat/test/internal/cli/init/package-manager.ts
index eb24a9bca1a..89bebb8f0ca 100644
--- a/v-next/hardhat/test/internal/cli/init/package-manager.ts
+++ b/v-next/hardhat/test/internal/cli/init/package-manager.ts
@@ -1,9 +1,6 @@
 import assert from "node:assert/strict";
 import { afterEach, beforeEach, describe, it } from "node:test";
 
-import { useTmpDir } from "@nomicfoundation/hardhat-test-utils";
-import { writeUtf8File } from "@nomicfoundation/hardhat-utils/fs";
-
 import {
   getDevDependenciesInstallationCommand,
   getPackageManager,
@@ -11,40 +8,52 @@ import {
 } from "../../../../src/internal/cli/init/package-manager.js";
 
 describe("getPackageManager", () => {
-  useTmpDir("getPackageManager");
-
   let originalUserAgent: string | undefined;
   beforeEach(() => {
     originalUserAgent = process.env.npm_config_user_agent;
-    process.env.npm_config_user_agent = "npm"; // assume we are running npm by default
   });
 
   afterEach(() => {
     process.env.npm_config_user_agent = originalUserAgent;
   });
 
-  it("should return pnpm if pnpm-lock.yaml exists", async () => {
-    await writeUtf8File("pnpm-lock.yaml", "");
-    assert.equal(await getPackageManager(process.cwd()), "pnpm");
-  });
+  const fixtureValues = [
+    {
+      agentString: "npm/11.6.1 node/v24.10.0 linux arm64 workspaces/false",
+      expected: "npm",
+    },
+    {
+      agentString: "pnpm/10.18.3 npm/? node/v24.10.0 linux arm64",
+      expected: "pnpm",
+    },
+    {
+      agentString: "yarn/1.22.22 npm/? node/v24.10.0 linux arm64",
+      expected: "yarn",
+    },
+    {
+      agentString: "yarn/4.10.3 npm/? node/v24.10.0 linux arm64",
+      expected: "yarn",
+    },
+    {
+      agentString: "bun/1.3.1 npm/? node/v24.3.0 linux arm64",
+      expected: "bun",
+    },
+    {
+      agentString: "deno/2.5.6 npm/? deno/2.5.6 linux aarch64",
+      expected: "deno",
+    },
+  ];
 
-  it("should return pnpm if invoked from pnpx", async () => {
-    assert.equal(await getPackageManager(process.cwd()), "npm");
-    process.env.npm_config_user_agent =
-      "pnpm/10.4.1 npm/? node/v23.2.0 linux x64";
-    assert.equal(await getPackageManager(process.cwd()), "pnpm");
-  });
+  it("Should work for all the fixture values", () => {
+    for (const fixture of fixtureValues) {
+      process.env.npm_config_user_agent = fixture.agentString;
 
-  it("should return npm if package-lock.json exists", async () => {
-    await writeUtf8File("package-lock.json", "");
-    assert.equal(await getPackageManager(process.cwd()), "npm");
-  });
-  it("should return yarn if yarn.lock exists", async () => {
-    await writeUtf8File("yarn.lock", "");
-    assert.equal(await getPackageManager(process.cwd()), "yarn");
-  });
-  it("should return npm if no lock file exists", async () => {
-    assert.equal(await getPackageManager(process.cwd()), "npm");
+      assert.equal(
+        getPackageManager(),
+        fixture.expected,
+        "Incorrect package manager for " + fixture.expected,
+      );
+    }
   });
 });
 
@@ -150,6 +159,26 @@ describe("installsPeerDependenciesByDefault", () => {
       assert.equal(actual, false);
     });
   });
+
+  describe("for bun", () => {
+    it("should always return true", async () => {
+      const actual = await installsPeerDependenciesByDefault(
+        process.cwd(),
+        "bun",
+      );
+      assert.equal(actual, true);
+    });
+  });
+
+  describe("for deno", () => {
+    it("should always return false", async () => {
+      const actual = await installsPeerDependenciesByDefault(
+        process.cwd(),
+        "deno",
+      );
+      assert.equal(actual, false);
+    });
+  });
 });
 
 describe("getDevDependenciesInstallationCommand", () => {
@@ -157,12 +186,24 @@ describe("getDevDependenciesInstallationCommand", () => {
     const command = getDevDependenciesInstallationCommand("pnpm", ["a", "b"]);
     assert.equal(command.join(" "), 'pnpm add --save-dev "a" "b"');
   });
+
   it("should return the correct command for npm", async () => {
     const command = getDevDependenciesInstallationCommand("npm", ["a", "b"]);
     assert.equal(command.join(" "), 'npm install --save-dev "a" "b"');
   });
+
   it("should return the correct command for yarn", async () => {
     const command = getDevDependenciesInstallationCommand("yarn", ["a", "b"]);
     assert.equal(command.join(" "), 'yarn add --dev "a" "b"');
   });
+
+  it("should return the correct command for bun", async () => {
+    const command = getDevDependenciesInstallationCommand("bun", ["a", "b"]);
+    assert.equal(command.join(" "), 'bun add --dev "a" "b"');
+  });
+
+  it("should return the correct command for deno", async () => {
+    const command = getDevDependenciesInstallationCommand("deno", ["a", "b"]);
+    assert.equal(command.join(" "), 'deno add "npm:a" "npm:b"');
+  });
 });