Cheaper LLM labelling

I have a small project where I needed to label commits as either “maintenance” or “new development”. The obvious way to do it is with a cheap but relatively capable LLM, like GPT 5.6 Luna. I tested it on a small set of commits and manually verified its labelling, and it emitted the same label as I would have for the entire test set. That was good enough for me to roll out on a wider scale.

If we have Simon Willison’s llm CLI tool installed (and you should – it’s great!), we can call it in a pipe from Perl, and read its response. My script had a loop that retried the request a few times, but without that bookkeeping, the code for this is simple enough.

sub classify {
    my ($msg) = @_;
    my $pid = open2(
        my $output,
        my $prompt,
        'llm -m openrouter/openai/gpt-5.6-luna'
    );
    print $prompt prompt_template($msg);
    close $prompt;

    chomp(my $result = do { local $/; <$output> });
    waitpid($pid, 0);

    return $result;
}