A Claude Code user has highlighted several prompt-caching behaviors that can cause long sessions to consume significantly more usage than expected.
Reddit user u/virtualunc said they found the details while going through Claude Code’s documentation rather than its changelog.
The biggest issue involves how long Claude Code keeps the main conversation cached.
Prompt Cache Drops From One Hour to Five Minutes
For subscription users who are still within their included plan usage, Claude Code keeps the main conversation’s prompt cache alive for one hour.
However, once the user exceeds that allowance and starts using additional usage credits, the cache time-to-live drops to just five minutes.
That means the gap before Claude has to process the conversation again becomes 12 times shorter, even though the user is still working in the same session.
Users accessing Claude Code through an API key or cloud provider get the five-minute cache by default.
Your Claude Code prompt cache drops from an hour to five minutes the second you pass your plan limit
byu/virtualunc inClaudeAI
Subagents Already Use a Five-Minute Cache
The longer cache applies only to the main conversation.
Other Claude Code activity, including subagents, workflows, compaction, and session-title generation, uses a five-minute cache regardless of the subscription tier.
As a result, returning to a subagent after 10 minutes can require its context to be processed again from scratch, even on a Max subscription.
Users Can Extend the Cache
According to the Reddit post, users can change this behavior by setting promptCacheTtl to 1h or using the CLAUDE_CODE_PROMPT_CACHE_TTL environment variable.
The subagentPromptCacheTtl setting controls the cache duration for other requests, including subagents.
These controls require Claude Code v2.1.242 or newer, and API-key users can use them as well.
Switching Models Rebuilds the Cache
Another important detail involves switching models during an active session.
Changing models causes Claude Code to read the entire conversation history again with no cache hits.
This can become especially noticeable with opusplan.
When Claude Code switches between Opus for planning and another model for execution, each move into or out of plan mode counts as a model switch. Repeatedly moving between planning and building can therefore rebuild the cache each time.
Agent Teams Can Use Around 7x More Tokens
Agent teams can also consume substantially more usage than a normal Claude Code session.
The documentation states that teams can use roughly seven times as many tokens when teammates remain in plan mode.
Each teammate maintains its own context, which increases the total amount of processing required.
/usage Can Show Your Cache Hit Rate
Users can check their own cache performance by running /usage.
Starting with Claude Code v2.1.251, the command includes a Prompt cache (main) line showing the cache hit rate.
From v2.1.260 onward, Claude Code can also identify the likely reason for the most recent cache miss.
The findings help explain why long Claude Code sessions can suddenly start consuming more usage even when the actual workload has not changed.
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