Claude Thermos

claude-thermos

Stop paying to rebuild your Claude Code cache. When your main agent waits on a subagent for more than 5 minutes, its prompt cache silently expires, and the next turn re-encodes your entire conversation at the write rate instead of reading it back cheap. On long sessions with many subagents that's roughly 20% of your bill. claude-thermos keeps the cache warm so you never pay that tax.

Use

Run Claude Code exactly as you normally would, but through claude-thermos with uvx:

Requires Python 3.11+ and the claude CLI on your PATH.

That's it. Warming runs automatically in the background. To disable it for a run without changing the command, set CLAUDE_THERMOS_DISABLE=1.

Tuning (all optional):

Choosing which claude to run

By default claude-thermos launches the claude found on your PATH. Point
it at a different binary with --bin, or the CLAUDE_THERMOS_BIN environment
variable. A bare name is looked up on PATH (so --bin claude-nightly
works); a full path is used as-is. This is handy for a vendored build or a
wrapper that exports a different CLAUDE_CONFIG_DIR per account.

The flag must come before any passthrough claude args.

Daemon mode (shared proxy for the IDE and multiple terminals)

The default command warms only the claude process it launches. Clients that
launch claude themselves — the VSCode/Claude Code extension, which spawns
its own bundled binary — never go through it, and neither do other terminals.

claude-thermos serve runs the warming proxy as a standalone daemon on a
fixed loopback port. Point any client at it and they all share one warmer:

For the VSCode extension, make sure its process inherits that environment
variable (on macOS, launchctl setenv ANTHROPIC_BASE_URL http://127.0.0.1:8787
before launching the app; or export it in the…