Ownership note first, because it matters for a tool you'd build a testing program on: [OpenAI](/entry/notebooklm-vs-chatgpt-projects-vs-claude-projects-which-for-research-2026) acquired Statsig in September 2025 and its founder became OpenAI's CTO of Applications. The engineering team stayed at OpenAI; in May 2026 Amplitude took over the Statsig brand and customer base and now runs it as a product. So "Statsig" today is an Amplitude offering.
| Free tier | Paid model | Meters on | |
|---|---|---|---|
| PostHog | 1M events/mo (all products) | usage-based | events + flag requests |
| GrowthBook | generous free / open-source core | Pro $20/seat/mo | seats (traffic unlimited) |
| Statsig (Amplitude) | free entry | usage-based, no per-seat charge | events |
GrowthBook is the open-source, warehouse-native option — it runs experiment analysis against your existing data warehouse, so you're not shipping event data to another vendor. Pricing is per-seat and predictable ($20/seat Pro), with unlimited traffic. A 25-person team pays about $1,000/month. Best when data governance and self-hosting matter, or when your traffic is huge and you don't want it driving the bill.
Statsig (now Amplitude) is the managed, real-time option with the most automated experiment analysis — sequential testing, CUPED variance reduction, automatic heterogeneous-effect detection. No per-seat charge, so a large platform team isn't penalized for adding people; you pay on event volume. Strong if you want sophisticated stats without building them.
PostHog bundles experimentation with analytics, session replay, flags and surveys under its 1M-events-free tier — the best value if you want all of that in one platform and one bill, with the caveat that costs rise with event volume and flag-check volume.
Warehouse-native, predictable seats, self-host option: GrowthBook. Want the deepest automated experiment stats, managed: Statsig. Want experimentation bundled with the rest of the product-analytics stack: PostHog.