# Culpa vs Arize > Arize AX meters spans and ingestion volume with 15-day retention on its free tier. Culpa prices calls in exact decimal and forecasts the month. URL: https://getculpa.com/culpa-vs-arize Last reviewed: 2026-08-03 ## Answer Arize AX is an agent observability and evaluation platform metered on trace spans and ingestion volume, with Phoenix as its open-source counterpart. Culpa, a local-first LLM cost, margin, and forecast ledger, prices each provider call from a versioned price book, attributes it to a customer against revenue, and forecasts next month with a range. ## Why this happens Arize meters two things at once and neither is money. AX Free covers 25k trace spans a month and 1 GB of ingestion with 15-day retention. AX Pro is $50 a month for 50k spans and 10 GB with 30-day retention. Both are SaaS, both give unlimited users and unlimited evals, and Phoenix is the open-source option if you'd rather run it yourself. The shape to notice is that a span count and an ingestion volume can both be growing while your model spend falls, because richer traces and smaller prompts pull in opposite directions. Arize is built for the question of whether an agent behaved, which is a real and hard question. It doesn't publish margin against revenue or a forecast of spend, and 15 days of retention on the free tier is the practical limit on how far back any cost question can reach. ## What this usually looks like - Your span count doubled after a refactor and your model bill didn't move. - You can prove an agent behaved and not what the run cost. - Retention expired before the monthly cost review asked its question. - Ingestion volume grew because traces got richer, not because usage did. - Nobody can name which customer's agent runs are the expensive ones. ## Common mistakes - Using span count as a stand-in for spend. Why it hurts: Spans track how you instrumented the code. Spend tracks tokens. Those move independently. Do instead: Price the calls from a rate book and keep spans for behaviour. - Picking a tier on span count alone. Why it hurts: Arize meters ingestion volume too, so a verbose trace can hit the GB ceiling long before the span ceiling. Do instead: Check both meters against your own traffic before committing. - Assuming an open-source counterpart means the same product. Why it hurts: Phoenix and AX are published as different things, and the retention and hosting differ. Do instead: Decide which one you're actually running before you build reporting on it. ## Self-check - Count the spans one agent run emits, then check it against your tier. - Check your ingestion volume separately from your span count. - Ask what a single agent run costs in provider spend, not in spans. - Find your retention window and compare it to your reporting cycle. ## When instrumentation moves the meter and spend stays still Arize AX Free publishes 25k trace spans a month. Take an agent that made 5 spans per run before someone instrumented the retrieval steps, and 12 after, with identical model calls throughout. Rates and allowances are published. The span shape is modelled. at 5 spans per run, 25,000 spans covers 5,000 runs a month at 12 spans per run, the same allowance covers 2,083 runs runs supported fell 58% with no change to any model call provider spend across both cases is identical to the cent The meter measured the instrumentation, not the workload. That's fine for observability billing and it's why a span-based tool can't answer a spend question, which needs tokens priced against a rate book rather than events counted. ## Cost figures Every figure carries its confidence and its source. For each provider-reported figure below, its own source line names the published record it came from, the date that record was read, and any aggregation applied to it. - $50 per month, Arize AX Pro's published price [provider-reported] Source: arize.com/pricing, read 2026-08-03. AX Pro covers 50k trace spans a month, 10 GB ingestion volume and 30-day retention on SaaS with unlimited users. AX Free covers 25k spans, 1 GB and 15-day retention. Phoenix is published separately as open source. ## FAQ Q: What does Arize AX cost? A: AX Free covers 25k trace spans a month, 1 GB of ingestion and 15-day retention, with unlimited users and evals. AX Pro is $50 a month for 50k spans, 10 GB and 30-day retention. Both are SaaS. Published on arize.com/pricing, read 2026-08-03. Q: Does Arize track LLM cost? A: Its published feature set is built around traces, spans and evaluation rather than a rate book. Nothing on its pricing or product pages claims margin against revenue or a forecast of spend, as read on 2026-08-03. Treat any cost column you see as attribution rather than as a priced ledger. Q: What's the difference between Arize AX and Phoenix? A: Arize publishes AX as its managed AI engineering platform and Phoenix as open-source observability and evals. They're presented as separate products with different hosting, so decide which one you're running before building reporting on either. Q: Can I run Arize and Culpa together? A: That's the intended shape. Arize answers whether the agent behaved. Culpa prices the calls it made, sets them against what the customer pays, and forecasts the month. The two read the same traffic and answer different questions. ## Sources - Arize: https://arize.com - Arize AX pricing: https://arize.com/pricing/ Run the free Cost Leak Scan: https://app.getculpa.com/scan?source=pseo&slug=culpa-vs-arize&cluster=competitor Machine-readable index of every guide: https://getculpa.com/api/pages Human-readable index of every guide: https://getculpa.com/guides Site overview: https://app.getculpa.com/llms.txt Privacy: Culpa runs on your infrastructure. Your prompts and responses never leave it. Culpa counts calls to run your plan, and it fails open, so if it ever breaks your app keeps running.