AI Daily Token Budget

Per-user daily token cap that prevents cost-amplification abuse. A single authenticated user cannot exhaust the AI quota for all other users by running many expensive requests.

Config ($lib/server/config.ts)

At current model prices this caps spend at roughly $1–2 per user per day on premium models.

Redis Key Shape

ai:budget:{userId}:{YYYY-MM-DD}

TTL: 25 hours (TTL_SECONDS = 25 * 60 * 60). The extra hour past midnight ensures the key is still readable in the final minutes of a UTC day regardless of clock skew between app instances.

The {YYYY-MM-DD} segment is derived from new Date().toISOString().slice(0, 10) — always UTC.

API ($lib/server/ai/budget.ts)

checkUserBudget(userId)

Call at request entry — before any expensive model invocation:

import { checkUserBudget } from '$lib/server/ai/budget';

const budget = await checkUserBudget(userId);
if (!budget.allowed) return decisionResponse(budget);

Returns a Decision. On denial, retryAfterMs is set to milliseconds until UTC midnight so the client can show an accurate reset time.

Redis-unavailable behavior:

chargeTokens(userId, tokens)

Call in streamText.onFinish after the response completes:

import { chargeTokens } from '$lib/server/ai/budget';

// Inside streamText.onFinish:
await chargeTokens(userId, usage.totalTokens);

Uses Redis INCRBY followed by EXPIRE to set the TTL on first write of the day.

Check-Then-Charge Caveat (v1)

The gate and charge are not atomic. A burst of N parallel requests can each pass checkUserBudget before any has called chargeTokens. The daily total can overshoot by up to N × AI_MAX_TOKENS before the cap engages.

At current rates the worst-case overshoot is $0.20–0.50 — acceptable for v1. Upgrade to atomic pre-charge (reserve tokens before generation, reconcile after) if abuse data warrants it.

BOT_DETECTION_MODE Interaction

The token budget does not read BOT_DETECTION_MODE — it is always enforced when Redis is available. The mode flag is scoped to the captcha layer only.

Where Enforced

• Chat orchestrator ($lib/server/ai/chat-orchestrator.ts): checkUserBudget at request entry, chargeTokens in streamText.onFinish.

Related

• Live showcase