Cartesia vs OpenAI 2026
Published September 2, 2026 · This is a documentation-based comparison. Every figure below was read from the two vendors’ own sources on September 1, 2026 and carries that check date. No listening test has been run, so nothing here compares how the two providers sound.
The short answer
One of these is the cheapest way in and the other has the best paperwork, and almost nothing else about them is comparable. Cartesia’s $5-a-month Pro plan carries a commercial licence and instant voice cloning. OpenAI has no free tier of any kind for speech, prices its older models at $15 per million characters, and gates custom voices behind sales (Cartesia pricing, OpenAI pricing, both checked September 1, 2026).
The gap that should decide it for most buyers is data. OpenAI contractually excludes API content from training and names the speech endpoint explicitly. Cartesia takes an irrevocable, perpetual, sublicensable licence over your inputs and outputs by default, with an opt-out that is a manual form and applies only going forward.
And Cartesia has a calendar you must watch. Two model aliases stop working after October 20, 2026, at alias level — pinning a dated snapshot does not save you. OpenAI publishes deprecations too, but nothing that lands inside seven weeks.
Comparison basis: official documentation only, checked September 1, 2026 — no accounts created, no API calls made, no audio generated, no scores assigned (how we verify).
| Cartesia | OpenAI | |
|---|---|---|
| Entry price | $0 Free (no commercial licence, no cloning); $5/month Pro adds both | No free tier. Pay per use from the first character |
| Rate | Credits: ~$0.038 per minute at Pro, falling to ~$0.028 at Scale | tts-1 $15.00 per 1M characters; gpt-4o-mini-tts $12.00 per 1M tokens audio output |
| Billing unit | Credits, converted to minutes by the vendor’s own approximations | Two units in one table — characters on the older models, tokens on the current one |
| Commercial use | Prohibited by default; Terms 4.1 permits “personal, non-commercial use only (unless commercial use is expressly permitted by your subscription tier)” | Granted; the services agreement assigns output rights outright |
| Output ownership | Cartesia disclaims ownership but §7.1 states it does not warrant that you own the output | Express assignment — the strongest language in our comparison set |
| Training on your data | On by default, under an irrevocable, perpetual, sublicensable licence. Opt-out is a manual form, forward-only | Contractually excluded, with the speech endpoint named in the per-endpoint table |
| Voice cloning | Instant from $5/month, 10-second sample; professional from $49/month | Custom voices exist but are sales-gated, and their supplemental terms are not published |
| Model lifecycle | sonic-2 and sonic-turbo stop working after October 20, 2026, at alias level | Legacy audio families carry a dated removal notice from July 20, 2026 |
| Liability cap | The greater of six months of fees or $100 — which on a $5 plan is $100 | Governed by the services agreement; see the OpenAI review |
| Audio quality | Not compared. Our listening benchmark has not run, so this page assigns no naturalness verdict to either provider. | |
On this page
Winners by category
Every winner below is a documentation-based judgment from published prices, terms and feature documentation. None is a test result, and the categories that require listening have no winner.
| Category | Winner | Why |
|---|---|---|
| Entry price | Cartesia | $5/month with a commercial licence and cloning against no free tier at all |
| Data terms | OpenAI | Contractual exclusion from training against a perpetual, irrevocable, sublicensable default licence |
| Output ownership | OpenAI | An express assignment against a clause declining to warrant that you own it |
| Cloning access | Cartesia | Self-serve from $5/month; OpenAI requires a sales conversation and publishes no terms for it |
| Model stability | OpenAI | Cartesia retires two aliases inside seven weeks, at a scope that defeats snapshot pinning |
| Expressive control | OpenAI | Plain-language delivery instructions; no other provider here documents that |
| Pricing legibility | Cartesia | One credit system. OpenAI runs two incompatible billing units with no published conversion |
| Free evaluation | Cartesia | A $0 tier exists, even without commercial rights. OpenAI has none |
| Contract currency | OpenAI | Cartesia’s terms are dated June 14, 2024 and name no model or lifecycle commitment |
| Naturalness | No winner | Requires listening. Our benchmark has not run |
| Pronunciation and difficult text | No winner | Requires listening. Our benchmark has not run |
Price and what it buys
These two cannot be normalized against each other, and the reason is worth stating plainly: Cartesia sells credits that it converts to minutes, and OpenAI sells characters on its older models and tokens on its current one. There is no published conversion between OpenAI’s audio tokens and characters, so a per-character comparison against gpt-4o-mini-tts is not possible from official information.
What can be compared is the entry point, and the gap is stark. Cartesia’s Pro plan is $5 a month and its bullets include both “Commercial use license” and “Instant voice cloning”. OpenAI has no free tier for speech and no subscription — you buy credits and spend them, and its tts-1 at $15 per million characters is roughly four times the standard rates of the cloud incumbents.
What this means for you: for a prototype or a side project that needs commercial rights, Cartesia is the cheaper answer by a wide margin. For anything where the paperwork matters more than the invoice, read the next section before deciding.
Data, training and ownership
This is the section that should decide most purchases, and the two providers sit at opposite ends of the market.
OpenAI excludes API content from training, contractually. Its documentation states: “Your data is your data. As of March 1, 2023, data sent to the OpenAI API is not used to train or improve OpenAI models (unless you explicitly opt in to share data with us)”, and the speech endpoint appears by name in the per-endpoint data table. The contractual form of that promise sits in clause 4.2 of its services agreement, verified August 11, 2026 — OpenAI’s policy pages returned an access error when we tried to re-read them on September 1, so that clause carries its original verification date rather than a fresh one.
Cartesia takes the opposite default. Clause 5.3(c) of its Terms grants Cartesia “a non-exclusive, irrevocable, perpetual, worldwide, royalty-free, fully paid, transferable, sublicensable right and license to use any Inputs and Outputs made available by you or otherwise generated in connection with your use of the Services at any point…” Every word there is load-bearing. The opt-out under 5.3(d) is a manual form rather than an account setting, and it is forward-only: it “will not affect any uses of Your Content (or improvements to the Models as a result) prior to that date.”
Ownership follows the same pattern. OpenAI’s clause 4.1 states the customer “owns all Output” and that OpenAI “assigns to Customer all OpenAI’s right, title, and interest, if any, in and to Output”. Cartesia disclaims ownership of your outputs in clause 5.3 — but clause 7.1, in capitals in the original, states: “THE CARTESIA ENTITIES DO NOT REPRESENT OR WARRANT THAT YOU ARE THE LEGAL OWNER OF ANY OUTPUT…” Those are not contradictory, and the difference matters: not claiming your output is not the same as confirming it is yours.
Cartesia also caps liability at the greater of six months of fees or $100. On a $5 plan, that ceiling is $100.
Model lifecycle
Both vendors publish deprecations, which is to their credit. Only one has a deadline inside two months.
Cartesia retires sonic-2 and sonic-turbo after October 20, 2026, and the scope is the part that catches people: the sunset applies at alias level, covering all snapshots, so pinning a dated version does not protect you. Only its sonic-3 entry is limited to a single dated snapshot. Migration is manual — “you will have to manually repoint production traffic” — though voice clones carry over with the same IDs. A second Cartesia sunset, on its Voice Changer endpoints, already passed on August 20, 2026 with no documented replacement, while the marketing page for that capability remains live.
OpenAI’s deprecation notice is dated July 20, 2026 and covers legacy audio, realtime and transcription families. A material share of its live audio price table therefore already carries an end date. Separately, its tts-1 lineage is described three different ways across three official pages — absent from the models index’s speech section, present with live model pages, present with live price rows.
What this means for you: if nobody on your team will be watching a vendor changelog, Cartesia is the riskier build. Not because it hides its changes — its tables are dated and explicit — but because it makes more of them.
Cloning and control
Cloning access runs strongly to Cartesia. Instant cloning from a 10-second sample is included at $5 a month; professional cloning from a 30-minute sample arrives at $49. OpenAI’s custom voices exist — the widespread belief that it offers preset voices only is out of date — but access is limited to eligible customers via sales, and the terms governing them sit in a supplemental agreement OpenAI references in plain text without a link and does not publish.
Neither enforces consent in the product. Cartesia’s Acceptable Use Policy places the obligation on you: you “may only submit your own voice and audio recordings or those of others with explicit consent”. Its Clone Voice API contains no occurrence of the word “consent” and no attestation field. OpenAI’s consent position for custom voices is in the unpublished supplemental agreement.
Control is OpenAI’s strongest card. Its instructions parameter takes plain-language direction over delivery rather than markup — a control surface nothing else in our comparison set documents. The trade is that OpenAI supports no SSML anywhere, and caps input at 4,096 characters per request, so longer scripts must be chunked with the seam handling that implies.
Voice quality, pronunciation and naturalness
We have not compared how these two providers sound, and we will not imply otherwise.
Our standardized listening benchmark is designed but not running. Until it does, this page carries no naturalness verdict, no pronunciation comparison and no scores for either provider. Both vendors publish quality claims of their own; those belong to them, and we do not repeat them as findings.
Choose Cartesia if · Choose OpenAI if
Choose Cartesia if:
- Budget is the binding constraint. $5 a month for a commercial licence and instant cloning is the cheapest such combination in our coverage.
- You need cloning without a sales conversation. OpenAI will not give you that.
- You want a free tier to evaluate on, even one without commercial rights.
- Someone will watch the changelog. The deprecation cadence is manageable if it is somebody’s job.
Choose OpenAI if:
- Your compliance position depends on inputs not training a model. This is the clearest difference between the two.
- Your legal review wants an express assignment of output rights. OpenAI has one; Cartesia declines to warrant ownership.
- You want to direct a voice in prose rather than markup. Instruction steering is genuinely distinctive.
- You need a model you can build on for years without an alias-level sunset seven weeks out.
Sources and what we could not verify
Every figure on this page was read from the two vendors’ official sources on September 1, 2026. Full detail is in the individual reviews: Cartesia review and OpenAI review. How we verify anything is described on the methodology page.
| Source | Used for |
|---|---|
| cartesia.ai/pricing | Plans, credits, minute approximations, cloning gates, commercial-licence bullet |
| Cartesia Terms of Service | Clauses 4.1, 5.3, 5.3(c), 5.3(d), 7.1, 7.2 (Last Revised June 14, 2024) |
| Cartesia Acceptable Use Policy | The consent warranty (Last revised July 23, 2025) |
| Cartesia API changes | Upcoming and executed sunsets, scope, error behaviour |
| Cartesia Clone Voice reference | Request fields — establishing the absence of a consent attestation |
| OpenAI developer pricing | Speech model prices, the two billing units, absence of a free tier |
| OpenAI text-to-speech guide | Instruction steering, custom-voice gating, the supplemental-agreement reference |
| OpenAI deprecations | The July 20, 2026 notice |
| OpenAI Services Agreement, clauses 4.1 and 4.2 | Ownership assignment and training exclusion — verified August 11, 2026; page unreachable September 1, 2026 |
What we could not verify
Honesty about gaps beats a page that looks complete. Genuinely unresolved as of September 1, 2026:
- How either provider sounds. No listening test has been run.
- Any per-character comparison against
gpt-4o-mini-tts. It bills in audio tokens and OpenAI publishes no conversion. - OpenAI’s contract clauses could not be re-read on September 1. Its policy pages returned an access error; the clauses carry their August 11, 2026 verification date.
- What OpenAI’s Text-to-Speech Supplemental Agreement says. Referenced without a link and not among the published policies.
- What Cartesia’s Pro-tier commercial licence actually covers. No page defines its scope or whether it survives cancellation.
- Whether Cartesia’s Voice Changer endpoints are actually off. Their sunset date passed while the marketing page stayed live.
- Any published rate limit or SLA for Cartesia. Only concurrency limits are documented.
Change log
September 2, 2026 — First publication as a documentation-based comparison. All figures read from official vendor sources on September 1, 2026 and dated accordingly.
Published September 2, 2026 · When our audio benchmark runs, this page gains a head-to-head listening test using the same prompts and documented conditions for both providers, and the naturalness and pronunciation rows gain real winners (methodology). Independence note: this page contains no affiliate links, and no vendor paid for placement or influenced the order — see how we make money and our editorial policy.