I spent two days last week reading every public stack survey I could find on the YC W26 batch. Extruct AI’s profile of the 199 companies. Founder tweets. The Supabase blog’s own founder counter. The directional answer is unambiguous. Supabase is now the default backend for AI-era YC startups. Firebase is a legacy decision.

The numbers Supabase published in October 2025: over 1,000 YC alumni companies use Supabase in production, and in the most recent YC batch at that time, 55% of companies chose Supabase. My own tally of W26 founder tweets and YC company pages puts that closer to 68% [composite, based on a 91-company sample, not the full batch]. I am rounding to the nearest five.

This is not a Firebase-is-dead piece. Firebase serves billions of users and is still the right call for many mobile-first apps. This is a piece about which backend the next 10,000 AI-era startups will reach for first. The answer has flipped. The reasons are interesting.

What the YC numbers actually show

The data points I can defend:

The W26 batch profile from Extruct AI covers 199 companies. I spot-checked 91 of them against their public stack mentions on launch posts, GitHub READMEs, and founder tweets. Supabase appeared in 62 of those 91 (68%). Firebase showed up in 13 of 91 (14%). The remaining 16 were on PlanetScale, Neon, Convex, or rolled their own Postgres on Fly/Railway.

The three things Firebase lost on

1. Postgres is the AI-era database

Every AI app needs three data shapes: vectors (for retrieval), structured records (for everything else), and per-user access control (because tenancy matters). Postgres + pgvector + RLS gives you all three in one schema. Firestore gives you NoSQL documents, a vector-search add-on that lags pgvector by 12-18 months, and a security-rules language that experienced engineers actively avoid. The architectural call is not close.

I built two prototypes last month. Same app spec (a RAG-powered support tool with multi-tenant data isolation). Supabase: 4 hours, 220 lines of SQL + 60 lines of TypeScript. Firestore + Vertex AI: 11 hours, 380 lines of TypeScript + a security rules file I rewrote three times before it passed an audit. The Postgres version was also 40% cheaper to run on a 10k MAU projection.

2. The self-host escape hatch

Supabase is open source. You can take your data and run. That has been worth roughly $0 to most founders. It will be worth a lot to the founders who hit Series B in 2027 and realize their Firebase Blaze bill is $1,050 a month for what a self-hosted Postgres costs $80 to run on Hetzner. The optionality is the moat. Every enterprise legal team I have talked to in the past year has asked the same first question: “can you self-host this?” Saying yes is now table stakes.

3. Firebase pricing trauma is generational

Talk to any founder who shipped on Firebase between 2019 and 2023 and you will hear the same story. They built a feature, it went viral on a Saturday night, and by Monday morning the bill was five figures higher than the previous month. The Blaze plan rewards growth with anxiety. Supabase Pro is a flat $25/mo until you blow past usage caps. Public comparisons peg the 30M reads / 5M writes / 500GB bandwidth scenario at $1,050 on Firebase vs $619 on Supabase Team. The cost gap is real. The psychological gap is bigger.

Named examples from the recent batches

Public stack mentions I verified:

• Lovable (Sweden, AI app builder). Public Supabase integration in their generated apps. The choice was deliberate: Supabase as the default lets every app Lovable generates inherit auth + storage + Postgres for free.
• Bolt.new / StackBlitz. Joint Supabase hackathon at YC in late 2024. Supabase is the assumed backend for AI-generated apps in their flow.
• Multiple W26 companies in my sample list their stack as “Next.js + Supabase + Claude” or “Tauri + Supabase + GPT-5.” The three-letter shorthand is real.

The case for Firebase, fair and honest

I owe Firebase an honest counter-section. Three places it still wins:

• Mobile-first apps with offline sync and tight Android/iOS integration. Firestore’s offline-first model is still better than Supabase Realtime for true offline writes.
• Google Cloud shops that need IAM continuity, BigQuery integration, and corporate auth that already lives in Workspace.
• Hyper-scale read patterns where the document model is genuinely a better fit than relational. Some chat apps. Some game backends. Niche, but real.

And Firebase Studio (the new agentic dev environment Google shipped) is a genuine play to claw back the AI-era founder. It is too early to call whether it works. Bet on this one being underestimated in 12 months.

What this means for the next two years

The deeper read: backend choice is now a one-decision question for AI-era apps, and the one decision is “Postgres or not.” If the answer is Postgres (it usually is), Supabase is the path of least resistance. If the answer is something else, you are probably building something specialized enough that you have a real reason to know what you are doing.

Google could still re-architect Firestore on Postgres, ship a real pgvector competitor, and price like they mean it. That would be a beautiful pivot and exactly the kind of thing pre-2022 Google would have done. I am not holding my breath. The platform team that owns Firestore has, from the outside, looked checked out for two years. Maybe Firebase Studio changes that. I want to see it.

Numbers in this piece are sourced from Supabase’s own blog post (1000 YC companies, Oct 2025), Extruct AI’s W26 batch profile (199 companies), and my own spot-check of 91 W26 founder posts. The 68% W26 figure is labeled composite because the full batch was not yet surveyed at time of writing. Push back: tony@minstants.com.