diff --git a/CHANGELOG.md b/CHANGELOG.md
index 89eb568b7..b2cfd255b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed Ask model selections reverting to a stale default after the model configuration changed during a browser session. [#1710](https://github.com/sourcebot-dev/sourcebot/pull/1710)
 - Upgraded `next` to `^16.3.8`. [#1709](https://github.com/sourcebot-dev/sourcebot/pull/1709)
 - Upgraded `seroval` to `^1.6.8`, `proxy-addr` to `^2.0.8`, `shell-quote` to `^1.12.0`, and `@grpc/grpc-js` to `^1.14.6`. [#1713](https://github.com/sourcebot-dev/sourcebot/pull/1713)
+- Upgraded `simple-git` to `^4.0.2`. [#1715](https://github.com/sourcebot-dev/sourcebot/pull/1715)
 - Upgraded `katex` to `^0.18.2` and `postcss-selector-parser` to `^7.1.6`. [#1717](https://github.com/sourcebot-dev/sourcebot/pull/1717)
 - Upgraded `engine.io` to `^6.6.11`, `source-map-js` to `^1.2.2`, `smol-toml` to `^1.9.0`, `fast-copy` to `^3.1.0`, and `dompurify` to `^3.4.16`. [#1714](https://github.com/sourcebot-dev/sourcebot/pull/1714)
 - Upgraded `golang.org/x/crypto` to `v0.56.0` and OpenTelemetry-Go exporters and SDK to `v1.45.0` in Zoekt. [#1716](https://github.com/sourcebot-dev/sourcebot/pull/1716)
diff --git a/packages/backend/package.json b/packages/backend/package.json
index e190cd797..3049f3dfd 100644
--- a/packages/backend/package.json
+++ b/packages/backend/package.json
@@ -33,6 +33,7 @@
         "@sentry/cli": "^2.42.2",
         "@sentry/node": "^10.71.0",
         "@sentry/profiling-node": "^10.71.0",
+        "@simple-git/argv-parser": "^2.0.1",
         "@sourcebot/db": "workspace:*",
         "@sourcebot/schemas": "workspace:*",
         "@sourcebot/shared": "workspace:*",
@@ -57,7 +58,7 @@
         "posthog-node": "^5.51.2",
         "prom-client": "^15.1.3",
         "redlock": "5.0.0-beta.2",
-        "simple-git": "^3.36.0",
+        "simple-git": "^4.0.2",
         "zod": "^3.25.76"
     }
 }
diff --git a/packages/backend/src/git.ts b/packages/backend/src/git.ts
index 8d2615358..6aaf3ea38 100644
--- a/packages/backend/src/git.ts
+++ b/packages/backend/src/git.ts
@@ -48,6 +48,28 @@ const createGitClientForPath = (
     }
 
     const parentPath = resolve(dirname(path));
+    const gitEnvironment: NodeJS.ProcessEnv = {
+        ...process.env,
+        ...environment,
+        /**
+         * @note on some inside-baseball on why this is necessary: The specific
+         * issue we saw was that a `git clone` would fail without throwing, and
+         * then a subsequent `git config` command would run, but since the clone
+         * failed, it wouldn't be running in a git directory. Git would then walk
+         * up the directory tree until it either found a git directory (in the case
+         * of the development env) or it would hit a GIT_DISCOVERY_ACROSS_FILESYSTEM
+         * error when trying to cross a filesystem boundary (in the prod case).
+         * GIT_CEILING_DIRECTORIES ensures that this walk will be limited to the
+         * parent directory.
+         */
+        GIT_CEILING_DIRECTORIES: parentPath,
+        /**
+         * Disable git credential prompts. This ensures that git operations will fail
+         * immediately if credentials are not available, rather than prompting for input.
+         */
+        GIT_TERMINAL_PROMPT: '0',
+    };
+
     const git = simpleGit({
         progress: onProgress,
         abort: signal,
@@ -55,28 +77,17 @@ const createGitClientForPath = (
             ...unsafe,
             ...additionalUnsafe,
         },
+        /**
+         * simple-git throws when an explicitly supplied git-related env var
+         * (e.g., GIT_CEILING_DIRECTORIES, GIT_ASKPASS) is not in this allowlist.
+         * We construct this environment ourselves, so every key is permitted.
+         * Values that enable unsafe behaviour are still gated by `unsafe` above.
+         *
+         * @see https://github.com/steveukx/git-js/releases/tag/simple-git%404.0.0
+         */
+        allowEnvironment: Object.keys(gitEnvironment),
     })
-        .env({
-            ...process.env,
-            ...environment,
-            /**
-             * @note on some inside-baseball on why this is necessary: The specific
-             * issue we saw was that a `git clone` would fail without throwing, and
-             * then a subsequent `git config` command would run, but since the clone
-             * failed, it wouldn't be running in a git directory. Git would then walk
-             * up the directory tree until it either found a git directory (in the case
-             * of the development env) or it would hit a GIT_DISCOVERY_ACROSS_FILESYSTEM
-             * error when trying to cross a filesystem boundary (in the prod case).
-             * GIT_CEILING_DIRECTORIES ensures that this walk will be limited to the
-             * parent directory.
-             */
-            GIT_CEILING_DIRECTORIES: parentPath,
-            /**
-             * Disable git credential prompts. This ensures that git operations will fail
-             * immediately if credentials are not available, rather than prompting for input.
-             */
-            GIT_TERMINAL_PROMPT: '0',
-        })
+        .env(gitEnvironment)
         .cwd({
             path,
         });
diff --git a/packages/web/package.json b/packages/web/package.json
index 3f926f5fe..b6c85bd7d 100644
--- a/packages/web/package.json
+++ b/packages/web/package.json
@@ -193,7 +193,7 @@
     "scroll-into-view-if-needed": "^3.1.0",
     "server-only": "^0.0.1",
     "sharp": "^0.35.3",
-    "simple-git": "^3.36.0",
+    "simple-git": "^4.0.2",
     "slate": "^0.117.0",
     "slate-dom": "^0.116.0",
     "slate-history": "^0.113.1",
diff --git a/packages/web/src/features/git/getFileBlameApi.ts b/packages/web/src/features/git/getFileBlameApi.ts
index d4b3c81c7..f922bd3f6 100644
--- a/packages/web/src/features/git/getFileBlameApi.ts
+++ b/packages/web/src/features/git/getFileBlameApi.ts
@@ -3,7 +3,7 @@ import { ServiceError, notFound, fileNotFound, invalidGitRef, unresolvedGitRef,
 import { withOptionalAuth } from '@/middleware/withAuth';
 import { getRepoPath } from '@sourcebot/shared';
 import { headers } from 'next/headers';
-import simpleGit from 'simple-git';
+import { simpleGit } from 'simple-git';
 import type z from 'zod';
 import { isGitRefValid, isPathValid } from './utils';
 import { fileBlameRequestSchema, fileBlameResponseSchema } from './schemas';
diff --git a/packages/web/src/features/git/getFileSourceApi.test.ts b/packages/web/src/features/git/getFileSourceApi.test.ts
index 9f08200be..0553fa394 100644
--- a/packages/web/src/features/git/getFileSourceApi.test.ts
+++ b/packages/web/src/features/git/getFileSourceApi.test.ts
@@ -1,12 +1,10 @@
 import { describe, it, expect, vi, beforeEach, type Mock } from 'vitest';
 
 // Hoist the mock function so it can be referenced in both the vi.mock factory
-// and the test body. The SUT imports simpleGit as a default export; the factory
-// maps both default and named exports to the same fn so both resolve identically.
+// and the test body.
 const mockSimpleGit = vi.hoisted(() => vi.fn());
 
 vi.mock('simple-git', () => ({
-    default: mockSimpleGit,
     simpleGit: mockSimpleGit,
 }));
 vi.mock('@sourcebot/shared', () => ({
diff --git a/packages/web/src/features/git/getFileSourceApi.ts b/packages/web/src/features/git/getFileSourceApi.ts
index 56eedc8ae..ef057362b 100644
--- a/packages/web/src/features/git/getFileSourceApi.ts
+++ b/packages/web/src/features/git/getFileSourceApi.ts
@@ -9,7 +9,7 @@ import { withOptionalAuth } from '@/middleware/withAuth';
 import { env, getRepoPath } from '@sourcebot/shared';
 import { Org, PrismaClient } from '@sourcebot/db';
 import { headers } from 'next/headers';
-import simpleGit from 'simple-git';
+import { simpleGit } from 'simple-git';
 import type z from 'zod';
 import { isGitRefValid, isPathValid } from './utils';
 import { fileSourceRequestSchema, fileSourceResponseSchema } from './schemas';
diff --git a/packages/web/src/features/git/getFilesApi.ts b/packages/web/src/features/git/getFilesApi.ts
index 87aac0e78..ac218d445 100644
--- a/packages/web/src/features/git/getFilesApi.ts
+++ b/packages/web/src/features/git/getFilesApi.ts
@@ -3,7 +3,7 @@ import { FileTreeItem } from "./types";
 import { notFound, ServiceError, unexpectedError } from '@/lib/serviceError';
 import { withOptionalAuth } from "@/middleware/withAuth";
 import { getRepoPath } from '@sourcebot/shared';
-import simpleGit from 'simple-git';
+import { simpleGit } from 'simple-git';
 import type z from 'zod';
 import { getFilesRequestSchema, getFilesResponseSchema } from './schemas';
 import { logger } from './logger';
diff --git a/packages/web/src/features/git/getFolderContentsApi.ts b/packages/web/src/features/git/getFolderContentsApi.ts
index 71b08440b..e2d1180ca 100644
--- a/packages/web/src/features/git/getFolderContentsApi.ts
+++ b/packages/web/src/features/git/getFolderContentsApi.ts
@@ -3,7 +3,7 @@ import { FileTreeItem } from "./types";
 import { notFound, unexpectedError } from '@/lib/serviceError';
 import { withOptionalAuth } from "@/middleware/withAuth";
 import { getRepoPath } from '@sourcebot/shared';
-import simpleGit from 'simple-git';
+import { simpleGit } from 'simple-git';
 import z from 'zod';
 import { compareFileTreeItems, isPathValid, normalizePath } from './utils';
 import { logger } from './logger';
diff --git a/packages/web/src/features/git/getTreeApi.ts b/packages/web/src/features/git/getTreeApi.ts
index fecbb958d..22bcb2e45 100644
--- a/packages/web/src/features/git/getTreeApi.ts
+++ b/packages/web/src/features/git/getTreeApi.ts
@@ -4,7 +4,7 @@ import { invalidGitRef, notFound, ServiceError, unexpectedError } from '@/lib/se
 import { withOptionalAuth } from "@/middleware/withAuth";
 import { getRepoPath } from '@sourcebot/shared';
 import { headers } from 'next/headers';
-import simpleGit from 'simple-git';
+import { simpleGit } from 'simple-git';
 import type z from 'zod';
 import { getTreeRequestSchema, getTreeResponseSchema } from './schemas';
 import { buildFileTree, isGitRefValid, isPathValid, normalizePath } from './utils';
diff --git a/yarn.lock b/yarn.lock
index 28ed17d9e..048361f9a 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -8269,19 +8269,19 @@ __metadata:
   languageName: node
   linkType: hard
 
-"@simple-git/args-pathspec@npm:^1.0.3":
-  version: 1.0.3
-  resolution: "@simple-git/args-pathspec@npm:1.0.3"
-  checksum: 10c0/91bfc99daa956df28e4efd683cd799f60c6d169fce6adf71a9efa80a6b5938fed4b03e55fa929cfd51aed64f3ada5c1e4edad45a3872dbd94d11924b3258b5bc
+"@simple-git/args-pathspec@npm:1.0.4, @simple-git/args-pathspec@npm:^1.0.4":
+  version: 1.0.4
+  resolution: "@simple-git/args-pathspec@npm:1.0.4"
+  checksum: 10c0/f62c09daf6a17734b2a13a186421bf0fdbdbd48782d1ca6d751027b2a9f515f11505da672489609f95335a0541d2fcf6d6fd6c2754919245109e92335e437b1b
   languageName: node
   linkType: hard
 
-"@simple-git/argv-parser@npm:^1.1.0":
-  version: 1.1.1
-  resolution: "@simple-git/argv-parser@npm:1.1.1"
+"@simple-git/argv-parser@npm:2.0.1, @simple-git/argv-parser@npm:^2.0.1":
+  version: 2.0.1
+  resolution: "@simple-git/argv-parser@npm:2.0.1"
   dependencies:
-    "@simple-git/args-pathspec": "npm:^1.0.3"
-  checksum: 10c0/2c21166f1bb7c4373e7b4e52bd0c7f333e58ea0ff5ac0b6c2d305835f4a2bcad1ef4bcce3cff63312ac55655ea7be3aba4c7c0c41e3ebcb8bee343f65bb92f5e
+    "@simple-git/args-pathspec": "npm:^1.0.4"
+  checksum: 10c0/7d2cd9852139ca3b524dcd91f6a887fa505cfb68c8813d7b849005566147365bb1e34f5450411c494fbd714a80c123058e65dc2ffc0b41d059e30bdc98e12223
   languageName: node
   linkType: hard
 
@@ -8846,6 +8846,7 @@ __metadata:
     "@sentry/cli": "npm:^2.42.2"
     "@sentry/node": "npm:^10.71.0"
     "@sentry/profiling-node": "npm:^10.71.0"
+    "@simple-git/argv-parser": "npm:^2.0.1"
     "@sourcebot/db": "workspace:*"
     "@sourcebot/schemas": "workspace:*"
     "@sourcebot/shared": "workspace:*"
@@ -8875,7 +8876,7 @@ __metadata:
     posthog-node: "npm:^5.51.2"
     prom-client: "npm:^15.1.3"
     redlock: "npm:5.0.0-beta.2"
-    simple-git: "npm:^3.36.0"
+    simple-git: "npm:^4.0.2"
     tsc-watch: "npm:^6.2.0"
     tsx: "npm:^4.21.0"
     typescript: "npm:^5.6.2"
@@ -9179,7 +9180,7 @@ __metadata:
     scroll-into-view-if-needed: "npm:^3.1.0"
     server-only: "npm:^0.0.1"
     sharp: "npm:^0.35.3"
-    simple-git: "npm:^3.36.0"
+    simple-git: "npm:^4.0.2"
     slate: "npm:^0.117.0"
     slate-dom: "npm:^0.116.0"
     slate-history: "npm:^0.113.1"
@@ -21493,16 +21494,16 @@ __metadata:
   languageName: node
   linkType: hard
 
-"simple-git@npm:^3.36.0":
-  version: 3.36.0
-  resolution: "simple-git@npm:3.36.0"
+"simple-git@npm:^4.0.2":
+  version: 4.0.2
+  resolution: "simple-git@npm:4.0.2"
   dependencies:
     "@kwsites/file-exists": "npm:^1.1.1"
     "@kwsites/promise-deferred": "npm:^1.1.1"
-    "@simple-git/args-pathspec": "npm:^1.0.3"
-    "@simple-git/argv-parser": "npm:^1.1.0"
+    "@simple-git/args-pathspec": "npm:1.0.4"
+    "@simple-git/argv-parser": "npm:2.0.1"
     debug: "npm:^4.4.0"
-  checksum: 10c0/4c22e57107535168f354e5abbbf6e618a7b39d76491ca225c70588520fbe86891f3b9a5c4f8a3fc0137e669aad2f0e11f6c6e677bfec07169cd18f29bf23cb77
+  checksum: 10c0/d028927258fa286d9d8e462f29ec6a37a32398acd7e53cef7fc81e70636c149d7359a542d1a4f8490b342d40d98e341c35c718734aec448fc24fdee88566e981
   languageName: node
   linkType: hard