Use it now
Useful4 Signal4
Set one variable and print mode keeps the model, tools and caches warm between prompts instead of rebuilding.
What's wrong with this entry?
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CLAUDE_CODE_PRINT_ENGINE_LOOP-p
What
In -p mode, Claude Code can build the query engine once and submit each prompt to it, keeping the model, tools, MCP clients and read-file cache warm across prompts, instead of rebuilding everything per prompt. Set CLAUDE_CODE_PRINT_ENGINE_LOOP to use it; unset, the existing per-prompt path runs.
Evidence
CLAUDE_CODE_PRINT_ENGINE_LOOP
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
Related
Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.
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v2.1.248
Autonomous /loop tick prompts now work for everyone
Both mention loop mode
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v2.1.229
A whitespace-only prompt gets its own error
Both mention print
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v2.1.242
--printwith--cloudcan message an existing cloud sessionBoth mention print