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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteIf your app keeps hitting voice API limits, choose a provider by the constraint it publishes—not by comparing a requests-per-minute figure with concurrent sessions or characters per minute. First identify whether you need text-to-speech (TTS), speech-to-text (STT), streaming, or a complete voice-agent API, then compare the relevant limit at your expected peak traffic. The figures below are from vendors’ live documentation checked on October 4, 2026; your effective quota can differ by account, model, project, plan, endpoint, and region.
Identify which limit is actually stopping your app
Rate, concurrency, and payload size are different constraints. A requests-per-minute (RPM) ceiling limits how many calls can begin over time; a concurrency ceiling limits how many calls or sessions can be active at once; a payload cap limits the size of an individual operation. Token, character, transaction-per-second (TPS), and audio-minute limits measure still other things. An API can have unused capacity in one measure and throttle you on another.
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Before comparing providers, record your expected peak request rate, simultaneous live sessions, typical and maximum text or audio per operation, deployment region, and required workflow: TTS, STT, or an end-to-end voice agent. Check the account’s actual model, project, subscription, and regional allocation as well. Published defaults are useful for screening, but they are not a guarantee of the capacity your account will receive.
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These are unlike capacity measures, not a leaderboard. Each entry applies only to the stated product and scope; consult the linked live documentation and your account settings before relying on a figure.
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| Provider and relevant workload | Published limit or example | Scope, payload, and adjustment notes |
|---|---|---|
| OpenAI API, including realtime audio | Limits can include RPM, requests per day (RPD), tokens per minute (TPM), tokens per day (TPD), images per minute (IPM), and audio minutes per minute; the first applicable cap reached can block requests. The GPT-Realtime model page’s tier table lists Tier 1 at 200 RPM, 1,000 RPD, and 40,000 TPM; Tier 2 at 400 RPM and 200,000 TPM; Tier 3 at 5,000 RPM and 800,000 TPM; Tier 4 at 10,000 RPM and 4,000,000 TPM; and Tier 5 at 20,000 RPM and 15,000,000 TPM. | Limits vary by model and apply at organization and project scope. The tier figures are listed values, not a promise of your effective allocation. The referenced GPT-Realtime model is marked deprecated, so verify the current model endpoint and its applicable limits. OpenAI’s guide says the account limits page and response headers can show applicable and remaining limits. OpenAI rate-limit guide; GPT-Realtime model page. |
| Deepgram, voice agent, STT, and TTS | For Pay As You Go, Voice Agent API is listed at up to 45 concurrent connections in each listed region; streaming STT at up to 150 concurrent requests and prerecorded STT at up to 50 for several models; Aura TTS at up to 15 concurrent REST requests or 45 concurrent streaming requests. | Concurrency is scoped to a project. The docs distinguish Pay As You Go, Growth, and Enterprise and list North America, Europe, Australia, and India; Growth and Enterprise allocations vary by region and product. Additional projects do not grant more concurrency; secondary self-serve projects are restricted to one concurrent stream. Deepgram directs customers seeking more concurrency to Growth/Enterprise sales. Deepgram API Rate Limits. |
| Google Cloud Text-to-Speech | The quotas page lists 1,000 requests per minute per project for voices without a dedicated quota; 200 requests per minute for Chirp 3; 500 for Studio; 1,000 for Neural2 and Polyglot; 100 per minute for long-audio synthesis operations; 100 concurrent streaming sessions per project; and 5,000 bytes per request. | These are project quotas, and model-specific quotas apply where listed. Request limits can be raised through the Cloud console; content limits cannot. The page notes Gemini-TTS values are model-specific and effective quotas can vary by project and may be increased on request. Google Cloud TTS quotas and limits. |
| Azure Speech, real-time TTS | For Standard (S0), the listed default is 30 transactions per second for standard and custom voices, adjustable up to 1,000 TPS. Free (F0) lists 20 transactions per 60 seconds and is not adjustable. Both list a 10-minute maximum generated-audio length per request. | Quota is not the only possible cause of throttling: Microsoft says most HTTP 429 errors for standard voices are due to limited backend capacity for a particular voice in the selected region. A higher quota may not resolve that issue; Microsoft suggests trying the voice’s native region or a more popular voice. Azure Speech quotas and limits. |
| PlayHT, streaming TTS | For POST /v2/tts/stream, Hacker/Pro is listed at 10 requests and 35,000 characters per minute; Startup at 25 requests and 87,500 characters per minute; Growth at 100 requests and 350,000 characters per minute. Enterprise is custom. |
Request and character ceilings are separate and both apply where the endpoint has both. The per-request maximum is 20,000 characters, so meeting the per-minute allowance does not remove the individual request cap. PlayHT says limits can be configured per client by contacting it; its 429 guidance says to wait no more than a minute before making new requests. PlayHT Rate Limits. |
| ElevenLabs, API requests | Documented subscription concurrency counts are Free 2, Starter 3, Creator 5, Pro 10, Scale 15, and Business 15 concurrent requests. | The documentation says the values may be revisited; ElevenAgents has separate concurrency limits. The 429 error too_many_concurrent_requests indicates a subscription concurrency ceiling, while system_busy indicates service load and is not proof that your plan quota is exhausted. ElevenLabs API 429 documentation. |
Which API fits your workload?
For streaming TTS or long text generation
Compare both the per-request payload cap and sustained character throughput. PlayHT publishes both request-per-minute and character-per-minute limits for its streaming endpoint, plus a 20,000-character per-request maximum. Google Cloud TTS publishes a 5,000-byte request cap and model-specific request quotas, so check whether your text size and chosen voice fit the relevant limit. Azure’s documented real-time TTS limits are expressed in TPS, but its voice- and region-specific backend capacity can still cause 429 responses.
For simultaneous speech sessions
Use a concurrency figure tied to the exact operation. Deepgram separates voice-agent connections, streaming STT, prerecorded STT, and Aura TTS, with region and plan differences. Google lists concurrent streaming sessions per project. ElevenLabs’ subscription counts are concurrent requests, not a general measure of every ElevenAgents workflow. Do not treat these figures as interchangeable session capacities.
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For an end-to-end voice agent
Check whether the published allowance covers the entire agent connection or only an underlying speech operation. Deepgram explicitly lists Voice Agent API concurrency alongside separate STT and TTS limits. OpenAI’s rate-limit guide describes multiple measures that can apply to a model, while the cited GPT-Realtime model page is marked deprecated; confirm the current endpoint and limits before designing around it. A TTS-only quota does not establish capacity for a complete agent stack.
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What to do when a voice API returns 429
Read the response body and error code before changing providers or raising a quota. HTTP 429 is a signal to diagnose, not a universal explanation: depending on the provider, it can mean rate exhaustion, concurrency, service capacity, or billing and usage restrictions.
- Rate or token limit: Compare the request’s model, organization or project, and workload size with all applicable limits. OpenAI notes that short enforcement windows can throttle bursts even when the displayed minute-level allowance appears sufficient.
- Concurrency limit: Check whether active requests or sessions exceed the plan’s documented cap. For ElevenLabs, distinguish
too_many_concurrent_requestsfromsystem_busy. - Backend capacity: For Azure standard voices, a 429 may reflect capacity for that voice in that region rather than your adjustable quota.
- Billing or usage restriction: OpenAI’s troubleshooting guidance notes that 429 can also reflect exhausted prepaid credits or an organization usage limit. A retry will not fix a hard usage or billing cap.
OpenAI’s guidance is to pace requests, avoid bursts, and follow Retry-After when provided; its official SDKs retry eligible rate-limit errors and honor that header when present. See OpenAI’s 429 troubleshooting guidance.
Make capacity predictable before switching providers
- Measure the workload: Capture peak calls per interval, concurrent sessions, input size, and region. Separate streaming traffic from one-shot synthesis or transcription.
- Match each measure to a cap: Estimate whether your workload is most likely to hit request rate, tokens or characters, payload size, TPS, or concurrency. If multiple limits apply, size for each one.
- Smooth bursts and bound active work: Use a queue or token bucket to pace submissions, and set an explicit ceiling on concurrent sessions. These are general engineering techniques, not guarantees that a particular architecture will improve provider capacity.
- Retry only when appropriate: For temporary throttling, honor provider retry guidance and use exponential backoff with jitter. Make retries idempotent where possible; do not blindly repeat requests after a billing, hard usage-cap, or non-retryable error.
- Monitor the failure context: Log provider, model, region, project, status and error code,
Retry-After, and workload size. Use vendor response headers or dashboards where available to compare actual limits and remaining capacity. - Request a legitimate quota change: Use the provider’s documented process—such as the Google Cloud console for request quotas, PlayHT support for per-client limits, or Deepgram Growth/Enterprise sales for higher concurrency. Confirm what changes, its scope, and whether it addresses the error you observed.
Choose on effective capacity, not the biggest number
No single published number identifies the best API for every constrained application: the vendors measure different workloads, and some limits are adjustable while others depend on voice, region, plan, or project. Select the service whose documented limit units and scope map to your measured bottleneck, then verify the allocation on your account and test the actual endpoint and region your app will use.
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