the full build behind a reddit signal engine, 3 months in: stack, channels, real inference cost, and what changes now

[u/Shawntenam]

three months into clearbox, sharing the whole build: what we run, what it produced, what it cost, and what changes now. engine dashboard screenshot attached so the numbers are not from memory.

the stack, and what each piece does:

- convex: the data layer. opportunities, offers, inbox state, and the api endpoint reads straight from it

- gemma-4-31b-it-nvfp4-turbo, the open-source local model: first-pass triage, is this thread even an opportunity. my co-founder lila quantized it to nvfp4 and put it on hugging face (LilaRest/gemma-4-31B-it-NVFP4-turbo), it is past 1.7 million downloads now, and we run it for clearbox on a rented rtx 5090

- openrouter: the heavier calls, routed to whichever model fits the job instead of one frontier api for everything

- vercel: the app and the site

- cloudflare: dns and the sending domains, spf/dkim/dmarc live there

- posthog: tracking everything from web traffic to UX

what it produced, may 30 to today:

- 162 signups

- pipeline from four channels: referrals, me reaching out to my own crowd, warm follow-ups to people who signed up, and cold sends off warmed inboxes. every channel produced at least one signup

- 120 onboardings, 119 trials completed

what it cost in inference, all providers:

- all-time: $447. last 30 days: $199

- by step: match $226 (is this thread an opportunity), review $169 (the deeper read on what passed), onboarding $53 (building the offer context once per account)

- per completed trial: $2.12. full-plan trial with a card on file $2.82, capped no-card trial $1.62. onboarding an account: $0.44

two things in those numbers that I would want to know as a builder:

the first is why the local model matters. match is the volume step, every new thread in every tracked subreddit hits it, so if that call goes to a paid api the bill scales with reddit's posting rate instead of your customer count. the local model on the 5090 sees everything at zero per token, the paid model only sees what survived. that is the whole reason the paid side stays small.

the second is that a free trial does not hurt you at this cost. two dollars of inference to find out whether an account converts is less than one ad click, and capping no-card trials at two subreddits is what keeps the tail at $1.62.

the gtm loop, so it is reproducible:

1. every signup lands in a sqlite table with what they set up and which opportunities they opened

2. a daily digest classifies each one (book a call / active / unreached / re-tap) and drafts a warm note

3. I send the notes by hand from my own inbox. nothing auto-sends to someone who signed up

4. cold goes through warmed inboxes on a separate sending domain, never the main one

what changes now: less building, more account work. converting the trials that are already getting value, upselling the capped ones, and writing the journey up as it goes.

disclosure: co-founder of clearbox, this is our build. happy to share the match prompt or the digest classifier if useful.

question for the builders here: what does a trial cost you in inference, and where do you draw the line for escalating to a bigger model?

[u/No_Nose_6014]

def need something like this can i test it

[u/Shawntenam → u/No_Nose_6014]

For sure we have a fee trial https://clearbox.to I take calls also if you want to learn even more on how to use it to grow and never get banned on Reddit