diff --git a/litellm/model_prices_and_context_window_backup.json b/litellm/model_prices_and_context_window_backup.json
index 07f9027313b..8c07ca35443 100644
--- a/litellm/model_prices_and_context_window_backup.json
+++ b/litellm/model_prices_and_context_window_backup.json
@@ -19403,6 +19403,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini-3.1-pro-preview": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "cache_creation_input_token_cost_above_200k_tokens": 2.5e-07,
@@ -19460,6 +19461,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini-3.1-pro-preview-customtools": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "cache_creation_input_token_cost_above_200k_tokens": 2.5e-07,
@@ -19614,6 +19616,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.5-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 1.5e-07,
         "input_cost_per_token": 1.5e-06,
         "input_cost_per_audio_token": 1e-06,
@@ -19665,6 +19668,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.6-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -19719,6 +19723,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.7-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -19773,6 +19778,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.1-pro-preview": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "cache_creation_input_token_cost_above_200k_tokens": 2.5e-07,
@@ -19830,6 +19836,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.1-pro-preview-customtools": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "cache_creation_input_token_cost_above_200k_tokens": 2.5e-07,
@@ -21337,6 +21344,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini/gemini-3.5-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 1.5e-07,
         "input_cost_per_audio_token": 1e-06,
         "input_cost_per_token": 1.5e-06,
@@ -21391,6 +21399,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini/gemini-3.6-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -21448,6 +21457,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini/gemini-3.7-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -21538,6 +21548,7 @@
         "tpm": 800000
     },
     "gemini/gemini-3.1-pro-preview": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "input_cost_per_token": 2e-06,
@@ -21595,6 +21606,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini/gemini-3.1-pro-preview-customtools": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "input_cost_per_token": 2e-06,
@@ -21733,6 +21745,7 @@
         "supports_vision": true
     },
     "gemini-3.5-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 1.5e-07,
         "input_cost_per_audio_token": 1e-06,
         "input_cost_per_token": 1.5e-06,
@@ -21785,6 +21798,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini-3.6-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -21840,6 +21854,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini-3.7-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
diff --git a/model_prices_and_context_window.json b/model_prices_and_context_window.json
index 07f9027313b..8c07ca35443 100644
--- a/model_prices_and_context_window.json
+++ b/model_prices_and_context_window.json
@@ -19403,6 +19403,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini-3.1-pro-preview": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "cache_creation_input_token_cost_above_200k_tokens": 2.5e-07,
@@ -19460,6 +19461,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini-3.1-pro-preview-customtools": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "cache_creation_input_token_cost_above_200k_tokens": 2.5e-07,
@@ -19614,6 +19616,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.5-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 1.5e-07,
         "input_cost_per_token": 1.5e-06,
         "input_cost_per_audio_token": 1e-06,
@@ -19665,6 +19668,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.6-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -19719,6 +19723,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.7-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -19773,6 +19778,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.1-pro-preview": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "cache_creation_input_token_cost_above_200k_tokens": 2.5e-07,
@@ -19830,6 +19836,7 @@
         "web_search_billing_unit": "per_query"
     },
     "vertex_ai/gemini-3.1-pro-preview-customtools": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "cache_creation_input_token_cost_above_200k_tokens": 2.5e-07,
@@ -21337,6 +21344,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini/gemini-3.5-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 1.5e-07,
         "input_cost_per_audio_token": 1e-06,
         "input_cost_per_token": 1.5e-06,
@@ -21391,6 +21399,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini/gemini-3.6-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -21448,6 +21457,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini/gemini-3.7-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -21538,6 +21548,7 @@
         "tpm": 800000
     },
     "gemini/gemini-3.1-pro-preview": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "input_cost_per_token": 2e-06,
@@ -21595,6 +21606,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini/gemini-3.1-pro-preview-customtools": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 2e-07,
         "cache_read_input_token_cost_above_200k_tokens": 4e-07,
         "input_cost_per_token": 2e-06,
@@ -21733,6 +21745,7 @@
         "supports_vision": true
     },
     "gemini-3.5-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 1.5e-07,
         "input_cost_per_audio_token": 1e-06,
         "input_cost_per_token": 1.5e-06,
@@ -21785,6 +21798,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini-3.6-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
@@ -21840,6 +21854,7 @@
         "web_search_billing_unit": "per_query"
     },
     "gemini-3.7-flash": {
+        "prompt_cache_min_tokens": 4096,
         "cache_read_input_token_cost": 7.5e-08,
         "cache_read_input_token_cost_flex": 3.75e-08,
         "input_cost_per_token": 7.5e-07,
diff --git a/tests/test_litellm/test_utils.py b/tests/test_litellm/test_utils.py
index efccdc4a986..4e75859c6df 100644
--- a/tests/test_litellm/test_utils.py
+++ b/tests/test_litellm/test_utils.py
@@ -2,6 +2,7 @@ import json
 import logging
 import os
 import sys
+from typing import Final
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
@@ -4384,6 +4385,45 @@ def test_get_prompt_cache_min_tokens_differs_per_platform_for_same_model(local_m
     )
 
 
+GEMINI_4096_CACHE_MIN_MODELS: Final = tuple(
+    prefix + base
+    for base in (
+        "gemini-3.5-flash",
+        "gemini-3.6-flash",
+        "gemini-3.7-flash",
+        "gemini-3.1-pro-preview",
+        "gemini-3.1-pro-preview-customtools",
+    )
+    for prefix in ("", "gemini/", "vertex_ai/")
+)
+
+
+def test_gemini_3_flash_and_31_pro_preview_resolve_4096_cache_minimum(local_model_cost_map: None) -> None:
+    """Regression for the cost map missing prompt_cache_min_tokens on these models: Google rejects
+    explicit caching below 4,096 tokens for them (https://ai.google.dev/gemini-api/docs/caching), so
+    the 1024 default sent cachedContents creates Vertex answered with a hard 400."""
+    wrong: Final = {
+        model: get_prompt_cache_min_tokens(model=model)
+        for model in GEMINI_4096_CACHE_MIN_MODELS
+        if get_prompt_cache_min_tokens(model=model) != 4096
+    }
+    assert not wrong, f"prompt_cache_min_tokens must be 4096: {wrong}"
+
+
+def test_gemini_4096_cache_minimum_present_in_root_cost_map() -> None:
+    """The root map ships to the CDN independently of the bundled backup, so both must carry the
+    minimum or proxies reading one of them regress to the 1024 default."""
+    root_map_path: Final = os.path.join(os.path.dirname(__file__), "..", "..", "model_prices_and_context_window.json")
+    with open(root_map_path) as f:
+        root_map: Final = json.load(f)
+    wrong: Final = {
+        model: root_map[model].get("prompt_cache_min_tokens")
+        for model in GEMINI_4096_CACHE_MIN_MODELS
+        if root_map[model].get("prompt_cache_min_tokens") != 4096
+    }
+    assert not wrong, f"prompt_cache_min_tokens must be 4096: {wrong}"
+
+
 def test_get_prompt_cache_min_tokens_unmapped_model_falls_back_to_default(local_model_cost_map: None) -> None:
     """get_model_info raises for a model it has no entry for. The resolver must swallow that and
     fall back to the default, otherwise the raise reaches callers that would read it as