diff --git a/.circleci/config.yml b/.circleci/config.yml
index 9063ba1d4a6..790cd6c7010 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -88,6 +88,36 @@ commands:
             rm -f /tmp/uv-install.sh
             echo 'export PATH="$HOME/.local/bin:$PATH"' >> "$BASH_ENV"
             export PATH="$HOME/.local/bin:$PATH"
+  install_rust:
+    description: "Install pinned rustup (1.28.2) and Rust toolchain (1.97.1) with checksum verification. Adds ~/.cargo/bin to PATH. Run this before any `uv sync` or `uv build` of the workspace: the root package builds litellm-rust through maturin, and on an image without cargo maturin fetches an unpinned rustup and a floating toolchain by itself."
+    steps:
+      - run:
+          name: Install Rust (rustup 1.28.2, toolchain 1.97.1)
+          command: |
+            case "$(uname -m)" in
+              x86_64)
+                RUSTUP_TRIPLE=x86_64-unknown-linux-gnu
+                RUSTUP_SHA256=20a06e644b0d9bd2fbdbfd52d42540bdde820ea7df86e92e533c073da0cdd43c
+                ;;
+              aarch64)
+                RUSTUP_TRIPLE=aarch64-unknown-linux-gnu
+                RUSTUP_SHA256=e3853c5a252fca15252d07cb23a1bdd9377a8c6f3efa01531109281ae47f841c
+                ;;
+              *)
+                echo "install_rust: unsupported architecture $(uname -m)" >&2
+                exit 1
+                ;;
+            esac
+            curl -sSLf -o /tmp/rustup-init \
+              "https://static.rust-lang.org/rustup/archive/1.28.2/${RUSTUP_TRIPLE}/rustup-init"
+            echo "${RUSTUP_SHA256}  /tmp/rustup-init" | sha256sum -c -
+            chmod +x /tmp/rustup-init
+            /tmp/rustup-init -y --no-modify-path --profile minimal --default-toolchain 1.97.1
+            rm -f /tmp/rustup-init
+            echo 'export PATH="$HOME/.cargo/bin:$PATH"' >> "$BASH_ENV"
+            export PATH="$HOME/.cargo/bin:$PATH"
+            rustc --version
+            cargo --version
   start_postgres:
     description: "Start a postgres-db container on port 5432 and wait until it accepts connections."
     parameters:
@@ -198,6 +228,7 @@ commands:
       - checkout
       - setup_google_dns
       - install_uv
+      - install_rust
       - restore_cache:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
@@ -312,6 +343,7 @@ jobs:
       - checkout
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Build the wheel
           environment:
@@ -344,6 +376,7 @@ jobs:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -417,6 +450,7 @@ jobs:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -491,6 +525,7 @@ jobs:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -542,6 +577,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -608,6 +644,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -648,6 +685,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -689,6 +727,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -722,6 +761,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - restore_cache:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
@@ -772,6 +812,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - restore_cache:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
@@ -823,6 +864,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -856,6 +898,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - restore_cache:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
@@ -902,6 +945,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -948,6 +992,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -990,6 +1035,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1036,6 +1082,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1083,6 +1130,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - restore_cache:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
@@ -1123,6 +1171,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1168,6 +1217,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1212,6 +1262,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1244,6 +1295,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1287,6 +1339,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1331,6 +1384,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1375,6 +1429,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1406,6 +1461,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1452,6 +1508,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1497,6 +1554,7 @@ jobs:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1547,6 +1605,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1571,6 +1630,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1597,6 +1657,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1698,6 +1759,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1793,6 +1855,7 @@ jobs:
           at: ~/project
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1881,6 +1944,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -1964,6 +2028,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -2096,6 +2161,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -2182,6 +2248,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -2278,6 +2345,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -2356,6 +2424,7 @@ jobs:
       - setup_google_dns
       # Remove Docker CLI installation since it's already available in machine executor
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -2437,6 +2506,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -2576,6 +2646,7 @@ jobs:
       - skip_if_unrelated_changes
       - setup_google_dns
       - install_uv
+      - install_rust
       - run:
           name: Install Dependencies
           command: |
@@ -2766,6 +2837,7 @@ jobs:
           category: client
       - setup_google_dns
       - install_uv
+      - install_rust
       - restore_cache:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
@@ -2908,6 +2980,7 @@ jobs:
           category: client
       - setup_google_dns
       - install_uv
+      - install_rust
       - restore_cache:
           keys:
             - v1-uv-cache-{{ checksum "uv.lock" }}
diff --git a/tests/test_litellm/test_circleci_rust_toolchain.py b/tests/test_litellm/test_circleci_rust_toolchain.py
new file mode 100644
index 00000000000..c35ced51e16
--- /dev/null
+++ b/tests/test_litellm/test_circleci_rust_toolchain.py
@@ -0,0 +1,148 @@
+"""Static guardrails for how CircleCI provisions Rust.
+
+The root package builds `litellm-rust` through maturin, so any job that runs
+`uv sync` or `uv build` compiles the bridge. The `cimg/python` images ship no
+Rust toolchain, and when cargo is missing maturin's `puccinialin` helper
+quietly provisions one itself: it fetches `rustup-init` from the unversioned
+`https://static.rust-lang.org/rustup/dist/<triple>/` path with no checksum and
+installs a floating `stable` toolchain. uv suppresses build-backend output on a
+successful sync, so that happens with nothing in the job log to show for it,
+and the compiler a job builds with changes whenever upstream publishes.
+
+Two invariants are pinned here:
+
+  1. No step list (job or reusable command) reaches a `uv sync` / `uv build`
+     without a Rust toolchain already provisioned ahead of it. That is the
+     `install_rust` command on Linux and an inline pinned rustup install in the
+     Windows job, so the check accepts either. A new job that syncs without one
+     falls back to the unpinned path, which is exactly the regression a static
+     check catches at PR time and a green CI run does not.
+  2. `install_rust` itself pins what it downloads: an explicit rustup version in
+     the URL, a verified SHA-256, and an exact toolchain version rather than a
+     channel name.
+
+The Windows job predates `install_rust` and provisions its toolchain inline, so
+invariant 2 is scoped to `install_rust`; invariant 1 covers both.
+"""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+import pytest
+import yaml
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+CONFIG = REPO_ROOT / ".circleci" / "config.yml"
+
+BUILDS_WORKSPACE = re.compile(r"\buv\s+(?:sync|build)\b")
+RUSTUP_ARCHIVE_URL = re.compile(r"https://static\.rust-lang\.org/rustup/archive/\d+\.\d+\.\d+/")
+EXACT_TOOLCHAIN = re.compile(r"--default-toolchain\s+\"?\d+\.\d+\.\d+\"?")
+
+
+def _config() -> dict[str, object]:
+    return yaml.safe_load(CONFIG.read_text())
+
+
+def _step_text(step: object) -> str:
+    """Flatten one step into the shell text it runs, or '' for a command reference."""
+    if isinstance(step, dict):
+        run = step.get("run")
+        if isinstance(run, str):
+            return run
+        if isinstance(run, dict):
+            command = run.get("command")
+            return command if isinstance(command, str) else ""
+    return ""
+
+
+def _without_comments(text: str) -> str:
+    return "\n".join(line for line in text.splitlines() if not line.lstrip().startswith("#"))
+
+
+def _provisions_rust(step: object) -> bool:
+    if step == "install_rust":
+        return True
+    text = _step_text(step)
+    return "rustup-init" in text and ("sha256sum" in text or "SHA256" in text)
+
+
+def _step_lists() -> dict[str, list[object]]:
+    config = _config()
+    lists: dict[str, list[object]] = {}
+    for kind in ("jobs", "commands"):
+        section = config.get(kind)
+        if not isinstance(section, dict):
+            continue
+        for name, body in section.items():
+            steps = body.get("steps") if isinstance(body, dict) else None
+            if isinstance(steps, list):
+                lists[f"{kind[:-1]} {name}"] = steps
+    return lists
+
+
+def _first_unprovisioned_build(steps: list[object]) -> str | None:
+    """Return the shell text of the first workspace build reached without Rust, if any."""
+    rust_ready = False
+    for step in steps:
+        if _provisions_rust(step):
+            rust_ready = True
+        text = _step_text(step)
+        if BUILDS_WORKSPACE.search(_without_comments(text)) and not rust_ready:
+            return text
+    return None
+
+
+def test_step_lists_exist() -> None:
+    lists = _step_lists()
+    assert "command install_rust" in lists
+    building = {
+        name
+        for name, steps in lists.items()
+        if any(BUILDS_WORKSPACE.search(_without_comments(_step_text(s))) for s in steps)
+    }
+    assert len(building) > 10, f"expected many workspace-building step lists, found {sorted(building)}"
+
+
+def test_no_workspace_build_without_a_provisioned_rust_toolchain() -> None:
+    offenders = {
+        name: build for name, steps in _step_lists().items() if (build := _first_unprovisioned_build(steps)) is not None
+    }
+    assert not offenders, (
+        "these CircleCI step lists run `uv sync`/`uv build` with no Rust toolchain provisioned first, "
+        "so maturin will download an unpinned rustup and a floating toolchain instead: "
+        f"{ {name: build.strip().splitlines()[0] for name, build in offenders.items()} }"
+    )
+
+
+@pytest.fixture(name="install_rust_command")
+def _install_rust_command() -> str:
+    steps = _step_lists()["command install_rust"]
+    return "\n".join(_step_text(step) for step in steps)
+
+
+def test_install_rust_pins_the_rustup_version_in_the_url(install_rust_command: str) -> None:
+    assert RUSTUP_ARCHIVE_URL.search(install_rust_command), (
+        "install_rust must download rustup-init from a version-pinned /rustup/archive/<x.y.z>/ URL; "
+        "the /rustup/dist/ path always serves whatever rustup is current"
+    )
+    assert "/rustup/dist/" not in install_rust_command
+
+
+def test_install_rust_verifies_the_installer_checksum(install_rust_command: str) -> None:
+    assert "sha256sum -c" in install_rust_command
+    assert re.search(r"RUSTUP_SHA256=[0-9a-f]{64}\b", install_rust_command), (
+        "install_rust must compare the downloaded installer against a hardcoded SHA-256 "
+        "taken from rust-lang's published .sha256 sidecar"
+    )
+    checksum_index = install_rust_command.index("sha256sum -c")
+    execute_index = install_rust_command.index("/tmp/rustup-init -y")
+    assert checksum_index < execute_index, "the checksum must be verified before the installer is executed"
+
+
+def test_install_rust_pins_an_exact_toolchain_version(install_rust_command: str) -> None:
+    assert EXACT_TOOLCHAIN.search(install_rust_command), (
+        "install_rust must pin an exact toolchain version (e.g. 1.97.1); a channel name like "
+        "stable/beta/nightly makes the compiler drift with whatever upstream published that day"
+    )