Configuration

Flowcat has no central config file and no settings framework (no figment, envy, or config crate, no flowcat.toml). That is deliberate: Flowcat is a library you embed, so configuration lives in two clearly separated places.

The important consequence: the runtime does not read provider API keys from the environment in production. Setting OPENAI_API_KEY does not make a running Flowcat pick it up — your embedder reads its own credentials however it likes and passes them to the provider constructor.

Contributing to Flowcat and running the live integration tests? Those use their own *_API_KEY environment variables — see Building and running tests.

1. Runtime environment variables

These are the variables the runtime itself reads. All are optional — each falls back to a built-in default. They tune the realtime (speech-to-speech) turn-taking and voice; they have no effect on the cascaded path.

Turn-taking, in plain terms. START_SENSITIVITY_LOW + a 500 ms PREFIX_PADDING means a brief caller sound — a backchannel ("uh-huh"), a cough, line noise — is not committed as a turn, so the agent stops cutting off its own speech. The end side stays eager (END_SENSITIVITY_HIGH + 350 ms trailing silence) so the agent still replies promptly once the caller actually finishes. Invalid values fall back to the default rather than erroring.

Defined in flowcat-core/src/realtime/gemini_live.rs (VadConfig::from_env) and flowcat-services/src/realtime/openai.rs.

2. Credentials & call settings (programmatic)

Everything else is configured in Rust, by your embedder, and passed into the relevant constructor. This is what keeps credentials on infrastructure you control — they never transit a Flowcat-owned config surface.

SIP / telephony — SipConfig

Passed to SipAgent::start(cfg). Telephony trunk credentials live here and reach nothing else.

Defined in flowcat-core/src/sip/agent.rs. See the Deployment guide for the firewall implications of the RTP range.

Provider credentials

Each STT / TTS / LLM / realtime service takes its key (and any voice / model settings) through its own constructor. Your embedder decides where those come from — its own env vars, a secrets manager, a vault. A common, simple choice is to read an env var named like the provider expects and pass it in:

#![allow(unused)]
fn main() {
// illustrative — your embedder owns this
let api_key = std::env::var("OPENAI_API_KEY")?;   // your choice, not the runtime's
let tts = OpenAiTts::new(&api_key, /* voice, model, … */);
}

The full set of provider constructors and their arguments is in flowcat-services; see the API reference for how to browse it as rustdoc.

Next: Deployment — build a release binary and ship it in your own VPC.