diff --git a/tests/benchmarks/conftest.py b/tests/benchmarks/conftest.py
index c9b31cfb7d7..8780ade5f82 100644
--- a/tests/benchmarks/conftest.py
+++ b/tests/benchmarks/conftest.py
@@ -6,8 +6,20 @@ virtual CPU. Work deferred to litellm's shared logging executor would therefore
 be attributed to whichever benchmark the valgrind scheduler resumes it under,
 flipping results between runs. Running the executor inline keeps each
 benchmark's cost self-contained and deterministic.
+
+The benchmarks also disable Python's cyclic garbage collector for the
+duration of the measurement window. CPython's GC is non-deterministic and
+runs on its own clock; a collection triggered mid-benchmark inflates the
+per-call instruction count in a way that depends on when (and whether) the
+collector happened to fire rather than on anything the code under test does.
+CodSpeed's per-iteration measurement is small enough (~hundreds of
+microseconds) that this noise dominates the signal for the multi-turn
+benchmark. ``mock_response`` already isolates the benchmarks from any
+real network I/O, so the synthetic allocations here have no live-tracing
+implications: deferring GC until the session ends is safe.
 """
 
+import gc
 from collections.abc import Callable, Iterator
 from concurrent.futures import Future
 from typing import ParamSpec, TypeVar
@@ -34,3 +46,21 @@ def inline_logging_executor() -> Iterator[None]:
     executor.submit = _submit_inline
     yield
     del executor.submit
+
+
+@pytest.fixture(autouse=True, scope="session")
+def disable_gc_during_benchmarks() -> Iterator[None]:
+    """Disable CPython's cyclic GC for the duration of the benchmark session.
+
+    CodSpeed counts instructions per measured iteration; a GC that happens to
+    run mid-iteration shows up as a deterministic-looking inflation that flips
+    between runs (because ``gc.collect()`` fires on its own clock). ``mock_response``
+    keeps the SDK from allocating anything that escapes the benchmark loop, so
+    the deferred collection at session teardown stays bounded.
+    """
+    gc.disable()
+    try:
+        yield
+    finally:
+        gc.enable()
+        gc.collect()