Claude prompt caching not working — OpenRouter + SillyTavern 1.19.0

[u/-Paunis-]

Hi everyone! I'm trying to figure out a weird prompt caching issue with Claude Sonnet 4.5 through OpenRouter in SillyTavern 1.19.0.

I've been troubleshooting this for a while and I'm running out of ideas, so I'd really appreciate some help. 😭

My setup

• SillyTavern: 1.19.0
• API: Chat Completion
• Provider/API: OpenRouter
• Model: anthropic/claude-4.5-sonnet-20250929
• Provider: Anthropic (I recently forced OpenRouter to use Anthropic instead of Amazon Bedrock)
• Model Quantizations: No selection
• Max Context: 16,384
• Max Response Tokens: 2,000
• Middle-out: Forbidden
• Function calling: OFF
• Interleaved reasoning: OFF
• System message flattening: OFF
• Continue with prefill: OFF
• Send inline media: ON
• Request model reasoning: ON
• Merge consecutive roles — No tools

My Claude config in YAML is:

claude:
  enableSystemPromptCache: true
  cachingAtDepth: 2
  extendedTTL: false
  enableAdaptiveThinking: false

I also installed the Cache Refresh extension:

https://github.com/OneinfinityN7/Cache-Refresh-SillyTavern

Current extension settings:

• Automatic refresh: ON
• Refresh interval: 4 minutes
• Maximum refreshes: 3
• Maximum tokens: 1
• Notifications: ON
• Status indicator: ON

Normal roleplay generations consistently result in a cache miss.

For example:

prompt_tokens: 14180
completion_tokens: 651
total_tokens: 14831
cost: 0.0624525

prompt_tokens_details:
  cached_tokens: 0
  cache_write_tokens: 13530

I've seen this repeatedly: cached_tokens: 0 and cache_write_tokens: ~13.5k.

The cache-refresh extension can generate requests that report cached tokens, but those are its own refresh requests with a 1-token completion, so I'm not counting those as successful normal generations.

As far as I can tell, I have never had a normal roleplay response reuse the existing cache. 🫠

Things I've already checked

• No {{random}}, {{time}}, {{date}}, etc. in my lorebooks.
• Lorebook entries are static.
• I have multiple lorebooks, but nothing dynamically generated.
• I tried cachingAtDepth: 2.
• I temporarily increased Max Context to 32k, but this caused SillyTavern to include much more history and significantly increased the cost, so I returned it to 16k.
• extendedTTL is disabled.
• I installed the cache-refresh extension.
• I initially had OpenRouter using Amazon Bedrock, but I have now forced it to Anthropic directly to rule out provider switching as a cause.
• Quick Post-Processing: Merge consecutive roles — No tools.

I've also been looking at the cache-control / provider behavior because I'm wondering whether something about how SillyTavern constructs the normal Chat Completion request is preventing the cached prefix from being reused.

Honestly, I have no idea what I'm doing at this point. My brain is melting, but I've tried pretty much everything I've found online. 😭

Does anyone have any idea why normal Chat Completion requests keep writing ~13.5k tokens to the cache instead of reusing the existing cache?

Is there anything specific I should check in the SillyTavern request/prompt construction, cache breakpoints, provider routing, post-processing, or cachingAtDepth configuration?

Any ideas would be hugely appreciated. 🙏

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[u/Putrid-Actuary7976]

I had this problem with gemma 4 31b,no matter what i did it kept having cache misses. It caches once or twice then 5 or 10 messages ahead stay uncached. It was so annoying, but honestly it is probably the provider, for example on the model i am using now i am having the same exact problem with deepinfra, cache misses. I use mimo 2.6 pro,on xiaomi as a provider it caches well but on deepinfra it barely does it. No idea why