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Agents are time-aware out of the box: every session knows today’s date and the current time in the session’s timezone. You don’t reference a variable or add anything to your prompt: “tomorrow morning” and “next Tuesday” ground correctly from the first turn, on every channel (voice, text, and phone).

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What the agent knows

Fish Audio injects two pieces of world context server-side: The time is refreshed on every turn, so it stays accurate through long conversations and past midnight.
Injection happens outside your configuration, so it never counts toward the system prompt’s character limit.
Both facts also exist as system variables for the cases where you want to template them yourself, for example into a webhook tool’s URL: {{system.today}} is the date at session creation as ISO YYYY-MM-DD, and {{system.timezone}} is the resolved IANA name (UTC when nothing resolves). There is no {{system.now}}: variables render once, when the session is created, so a templated clock would freeze at the opening. The per-turn time above is the one to rely on.

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Which timezone a session uses

The timezone is resolved once, when the session is created, taking the first that applies:
  1. timezone in the creation request: your explicit per-session choice, as an IANA name like Asia/Shanghai. An invalid name rejects the request with 422.
  2. The agent’s configured timezone: set on the agent in the Builder (Configuration → Timezone) or via the agent config API. Pin one when your agent serves a single region regardless of who calls.
  3. client_timezone: a hint with the end user’s browser timezone, sent automatically by the Web SDK in public-agent mode. Used only when neither of the above is set; an invalid hint is ignored rather than failing the session.
  4. The caller’s phone number: inbound calls infer the timezone from the caller’s country when that country has a single timezone.
  5. UTC otherwise.
In the browser, this means zero configuration: the SDK detects the visitor’s real timezone and the agent talks about “today” in the user’s local terms, not yours. With authenticated sessions, the SDK’s automatic hint doesn’t apply. Your backend creates the session, so set timezone (or forward the browser’s value as client_timezone) in the creation request:
API (curl)
Phone-number inference is country-level only. Countries that span several timezones (the US, Canada, Australia, Russia, Brazil) are skipped. Set the agent’s timezone for those. Calls that resolve nothing run in UTC.

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Turn it off

Time awareness is on by default. To withhold both the date and the per-turn time from a session (for example a role-play agent set on a fictional date, or a test that must be reproducible), set world_context: false when creating the session:

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Going further

Authenticated sessions

All session-creation parameters, including timezone and world_context.

Dynamic variables

Personalize the rest of the prompt at session creation.