🔴 Required Information
Describe the Bug:
VertexAiSessionService does not persist cache_metadata or usage_metadata fields when writing/reading Event objects to/from Agent Engine. This causes ContextCacheRequestProcessor to never find prior cache metadata, so context caching creates a new cache on every invocation instead of reusing existing ones.
Steps to Reproduce:
- Install
google-adk[eval]==1.25.1
- Configure an agent with
ContextCacheConfig in App():
app = App(
name="my_agent",
root_agent=root_agent,
context_cache_config= ContextCacheConfig( min_tokens=2048, ttl_seconds=1800, cache_intervals=10),)
- Run with in-memory sessions:
adk web — send the same prompt twice in the same session. Observe cacheMetadata in the dev UI showing cache_name reuse on the second turn.
- Run with Agent Engine sessions:
adk web --session_service_uri=agentengine://<your_engine_id> — send the same prompt twice in the same session. Observe that every turn creates a new cache with a different fingerprint; cache_name is never reused.
Expected Behavior:
cache_metadata and usage_metadata should round-trip through Agent Engine sessions the same way they do with InMemorySessionService. The second invocation in the same session should reuse the existing cache.
Observed Behavior:
With VertexAiSessionService, every invocation creates a new cache. The cacheMetadata in events shows a new fingerprint and increasing contents_count each time, with no cache_name reuse.
Environment Details:
- ADK Library Version: 1.25.1
- Desktop OS: macOS
- Python Version: 3.11
Model Information:
- Are you using LiteLLM: Yes/No
- Which model is being used: gemini-2.5-pro
🟡 Optional Information
Regression:
N/A — this has never worked with VertexAiSessionService as far as we can tell (tested 1.19.0 and 1.25.1).
Logs:
With InMemorySessionService (working):
cacheMetadata:
cache_name: "projects/798321343024/locations/us-central1/cachedContents/6261708034305687552"
expire_time: 1772555630.466322
fingerprint: "e8e3e4d5226b764d"
invocations_used: 2
contents_count: 2
created_at: 1772553830.466322
With VertexAiSessionService (broken — new cache every turn):
cacheMetadata:
fingerprint: "c3f575505d7ec95c"
contents_count: 6
Minimal Reproduction Code:
from google.adk.agents import Agent
from google.adk.app import App
from google.adk.context_cache import ContextCacheConfig
root_agent = Agent(
name="test_agent",
model="gemini-2.5-pro",
instruction="You are a helpful assistant.",
)
app = App(
name="test_app",
root_agent=root_agent,
context_cache_config=ContextCacheConfig(
min_tokens=2048,
ttl_seconds=1800,
cache_intervals=10,
),
)
# Works: adk web
# Broken: adk web --session_service_uri=agentengine://<engine_id>How often has this issue occurred?:
🔴 Required Information
Describe the Bug:
VertexAiSessionServicedoes not persistcache_metadataorusage_metadatafields when writing/reading Event objects to/from Agent Engine. This causesContextCacheRequestProcessorto never find prior cache metadata, so context caching creates a new cache on every invocation instead of reusing existing ones.Steps to Reproduce:
google-adk[eval]==1.25.1ContextCacheConfigin App():adk web— send the same prompt twice in the same session. ObservecacheMetadatain the dev UI showingcache_namereuse on the second turn.adk web --session_service_uri=agentengine://<your_engine_id>— send the same prompt twice in the same session. Observe that every turn creates a new cache with a different fingerprint;cache_nameis never reused.Expected Behavior:
cache_metadataandusage_metadatashould round-trip through Agent Engine sessions the same way they do with InMemorySessionService. The second invocation in the same session should reuse the existing cache.Observed Behavior:
With
VertexAiSessionService, every invocation creates a new cache. ThecacheMetadatain events shows a new fingerprint and increasingcontents_counteach time, with no cache_name reuse.Environment Details:
Model Information:
🟡 Optional Information
Regression:
N/A — this has never worked with VertexAiSessionService as far as we can tell (tested 1.19.0 and 1.25.1).
Logs:
With
InMemorySessionService(working):With
VertexAiSessionService(broken — new cache every turn):Minimal Reproduction Code:
How often has this issue occurred?: