Picking a text-to-speech (TTS) API comes down to three questions: do you like how it sounds, how fast does it answer, and how much does it cost? We answered all three for Cartesia and ElevenLabs, two of the bigger names in the space.
We ran the same scripts through each provider's flagship and fastest models. The flagships are Cartesia's sonic-3.5 and ElevenLabs' eleven_v3; the speed-tuned models are sonic-turbo and flash_v2.5.
Cartesia came out ahead on price and matched ElevenLabs on quality. ElevenLabs has a more extensive product suite around its voice models, which makes it convenient for content-creation tasks like video voiceover or subtitling.
Quality Across Four Scenarios
We put both flagships through four scripts, each stressing a different weak spot. The verdict up front is that there's very little between them. Both read all four cleanly, and either is good enough for narration, voice agents, or voiceover. If anything, sonic-3.5 sounds slightly more expressive out of the box, while eleven_v3 leans toward a more even delivery.
sonic-3.5
eleven_v3sonic-3.5eleven_v3sonic-3.5eleven_v3sonic-3.5eleven_v3The Fast Models Are Where Quality Slips
The speed-tuned models tell a different story, but only on the hardest script. Cartesia's sonic-turbo holds up across all four scenarios, but ElevenLabs' flash_v2.5 stumbles on the numbers test, garbling several of the figures and currency amounts that every flagship read without trouble. The same numbers script through each fast model:
sonic-turboflash_v2.5If your workload reads out prices, dates, or IDs and you want the cheaper, faster tier, definitely go with Cartesia.
Price Is the Clearest Difference
Cost is where the two providers differ most. For the top-quality models, Cartesia is roughly two to three times cheaper.
Cartesia charges the same rate for every model, so the flagship sonic-3.5 and the fast sonic-turbo cost the same. That rate drops as you commit to a larger plan, while ElevenLabs holds a flat published rate across its self-serve tiers (discounts are reserved for enterprise):
| Cartesia plan | Price/mo | Any model, per 1M characters |
|---|---|---|
| Pro | $5 | $50 |
| Startup | $49 | $39 |
| Scale | $299 | $37 |
The higher ElevenLabs cost can be worth it if you'll use its other products, such as the video generation studio, music generation, and dubbing, whereas Cartesia only offers voice AI features.
Latency: Both Fast, with One Slow Outlier
For responsiveness in real-time voice agents, time to first byte is what matters. We ran a basic latency test that accounts for network variation; here are the rough numbers you can expect:
eleven_v3 lands past the conversational-comfort mark. By design, it isn't built for real-time use.The outlier is eleven_v3, which is several times slower to first sound and isn't built for real-time. This is expected behavior, and ElevenLabs states it clearly.
Oddly, we measured almost no latency gap between Cartesia's turbo model and its flagship. They cost the same too, yet the flagship sounds clearly better, which makes it hard to see when you'd use the turbo model.
Code-Switching and Language Coverage
Bilingual scripts are a good stress test, so we wrote a passage where a native Spanish narrator speaks English but slips into Spanish mid-sentence, and ran it through a Spanish-native voice on each provider.
sonic-3.5eleven_v3Both switch cleanly at the language boundary. The wider gap is coverage: eleven_v3 supports more than 70 languages against sonic-3.5's 42, and ElevenLabs ships a far larger voice library plus a marketplace of licensed voices.
Where Each One Wins
CartesiaElevenLabsIn short: Use Cartesia when cost, real-time latency, and simple pricing matter most. Go for ElevenLabs when you need its breadth, the languages, the voice library, the expressive audio tags, and the creative tools built around the models.
Our Recommendation
For most production voice work, and especially for real-time agents at scale, start with Cartesia. It's cheaper, its pricing is honest and flat, and its flagship answers fast enough for conversation. Go for ElevenLabs when you need its larger voice library, its wider language coverage, or its broader creative toolkit.