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If your app is hitting voice API limits, first identify which kind of capacity is exhausted: requests or tokens per time period, simultaneous sessions, or the maximum payload accepted in one operation. These are different constraints, so no single provider limit is a fair measure of overall capacity. OpenAI, Deepgram, Google Cloud, Azure, PlayHT, and ElevenLabs publish different combinations of them; the right fit depends on your traffic shape, workload, region, and account-specific allocation.
Rate limits, concurrency limits, and payload limits are different
A rate limit caps how much work can arrive over time. Depending on the API, that might be requests per minute (RPM), tokens per minute (TPM), characters per minute, or transactions per second (TPS). A concurrency limit caps how many requests or live sessions can be active at once. A payload limit caps the size or duration of one request.
An app can stay below its RPM allowance and still exceed its simultaneous-session ceiling during a traffic spike. It can also have available request capacity but send a text payload larger than the endpoint accepts. Before comparing providers, estimate these workload characteristics:
- Peak request rate, including short bursts rather than just an hourly average.
- Maximum simultaneous calls, streams, or synthesis jobs.
- Average and largest text, audio, or token payload for each operation.
- Where requests will run, and which regions and voice models the app needs.
- Whether the product needs text-to-speech (TTS), speech-to-text (STT), streaming, or an end-to-end voice-agent service.
Limits can attach to a model, project, organization, subscription, endpoint, or region. A published default is not necessarily your effective allocation: confirm the limit shown in your own account or contract before designing around it. The vendor documentation figures below were checked on October 4, 2026; quota pages can change.
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Compare the published limits that match your workload
The figures below use different units and scopes, so they are not a provider ranking. Check the linked live documentation and your account for current, applicable limits.
| Provider and workload | Published capacity and scope | Payload, adjustments, and relevant caveats |
|---|---|---|
| OpenAI API and GPT-Realtime Rate-limit guide; GPT-Realtime model page |
OpenAI rate limits can be expressed as RPM, requests per day (RPD), TPM, tokens per day (TPD), images per minute (IPM), and audio-minutes per minute. The applicable limit reached first can throttle a request. Limits vary by model and apply at organization and project scope. The GPT-Realtime page’s tier table lists: Tier 1, 200 RPM, 1,000 RPD, and 40,000 TPM; Tier 2, 400 RPM and 200,000 TPM; Tier 3, 5,000 RPM and 800,000 TPM; Tier 4, 10,000 RPM and 4,000,000 TPM; Tier 5, 20,000 RPM and 15,000,000 TPM. | These are tier-table values, not a guarantee of an account’s allocation. The listed GPT-Realtime model is marked deprecated, so verify the current endpoint and its limits. The account limits page and response headers can help identify the applicable limit and remaining capacity. |
| Deepgram API Rate Limits |
Concurrency is scoped to a project and varies by plan, service, and region. In the Pay As You Go table, Voice Agent API allows up to 45 concurrent connections in each listed region: North America, Europe, Australia, and India. The same table lists up to 150 concurrent streaming STT requests and 50 pre-recorded STT requests for several models. Aura TTS is listed at up to 15 concurrent REST requests or 45 concurrent streaming requests. | Growth and Enterprise have higher documented allocations, but values vary across products and regions. Deepgram directs customers seeking higher concurrency to Growth or Enterprise sales. Additional projects do not grant more concurrency; secondary self-serve projects are restricted to one concurrent stream, and using projects to bypass limits violates its terms. |
| Google Cloud Text-to-Speech Quotas and limits |
Quotas are per project. The page lists 1,000 requests per minute for voices without a dedicated quota, 200 requests per minute for Chirp 3, and 100 concurrent streaming sessions. Other voice quotas include 500 requests per minute for Studio and 1,000 requests per minute for Neural2 and Polyglot; long-audio synthesis operations are listed at 100 requests per minute. Gemini-TTS quotas are model-specific. | The request payload limit is 5,000 bytes. Request limits can be raised through the Cloud console; content limits cannot. Effective quotas can vary by project, and the page says Gemini-TTS quotas may be increased on request. |
| Azure Speech Quotas and limits |
For real-time TTS, Standard (S0) has a default 30 TPS for standard and custom voices, adjustable up to 1,000 TPS. Free (F0) allows 20 transactions per 60 seconds and is not adjustable. | Both tiers list a 10-minute maximum generated-audio length per request. Microsoft says most HTTP 429 errors for standard voices stem from limited backend capacity for a particular voice in the selected region, rather than from the quota. Trying the voice in its native region or choosing a more popular voice may help; raising the quota alone may not address that cause. |
| PlayHT Rate Limits |
For POST /v2/tts/stream, the table lists paired request-per-minute and character-per-minute limits: Hacker/Pro, 10 requests and 35,000 characters; Startup, 25 requests and 87,500 characters; Growth, 100 requests and 350,000 characters. Enterprise is custom. |
The endpoint accepts up to 20,000 characters per request, so per-request size and per-minute throughput are separate constraints. Limits are configurable per client by contacting PlayHT. Its 429 guidance says new requests can be made after a short wait of no more than a minute. |
| ElevenLabs API 429 documentation |
The page lists concurrent-request limits by subscription: Free, 2; Starter, 3; Creator, 5; Pro, 10; Scale, 15; Business, 15. ElevenAgents has separate concurrency limits. | ElevenLabs says these values may be revisited. Its too_many_concurrent_requests error indicates a subscription concurrency limit; system_busy means service load prevented a request and does not prove the account exceeded its plan limit. |
Choose by the bottleneck your app actually has
For live voice agents and streaming sessions
Compare concurrent connections or sessions, not only requests per minute. Deepgram publishes concurrency by service, plan, project, and region; Google Cloud TTS lists streaming sessions per project; ElevenLabs publishes subscription concurrency and separates ElevenAgents limits. For an OpenAI voice workflow, inspect the current model’s applicable organization and project limits rather than treating a tier table for a deprecated model as a current allocation.
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For batch or high-volume speech generation
Compare the relevant request rate and payload cap together. PlayHT explicitly enforces both request and character throughput on its streaming endpoint, while Google Cloud TTS distinguishes voice-specific request quotas from a per-request byte limit. Azure’s Standard TTS allocation is measured in transactions per second, but a voice-specific regional capacity issue can still matter independently.
For speech recognition or a combined voice stack
Check limits for each API operation your app will call. Deepgram lists separate limits for streaming and pre-recorded STT, TTS, and Voice Agent API. OpenAI’s applicable dimensions may include request, token, image, or audio-minute measures depending on the model and workload. Do not infer the capacity of one service from another service offered by the same provider.
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How to verify or increase an allocation
- Identify the exact resource and scope. Record the provider, API endpoint, model or voice, project or organization, plan, and region used by the production request.
- Check the live limit and remaining capacity. Use the provider’s account or project quota page where available. OpenAI also documents response headers with limit and remaining values. Confirm whether the published figure is a default, an adjustable ceiling, or an allocation already applied to your account.
- Ask for an increase through the documented channel. Google Cloud says request quotas can be raised through the Cloud console, while content limits cannot. PlayHT says client limits can be configured by contacting it. Deepgram directs customers who need more concurrency to Growth or Enterprise sales. Azure’s Standard quota is adjustable within its documented ceiling; its Free quota is not. For other limits, consult the provider’s account page or support channel rather than assuming an increase is automatic.
- Recheck after any change. Validate the new allocation against the actual project, model, endpoint, and region used by your app. A higher general quota will not necessarily resolve an independent payload cap or backend capacity constraint.
Diagnose a 429 before deciding to retry
HTTP 429 means the request was refused for a reason that needs to be read from the response body and provider documentation; it is not a universal synonym for “too many requests.” OpenAI’s troubleshooting guidance identifies rate-limit throttling as well as exhausted prepaid credits and organization usage limits. Its support page recommends pacing requests, avoiding bursts, following Retry-After when supplied, and not blindly retrying a billing or hard usage-cap error. Official OpenAI SDKs retry eligible rate-limit errors and honor Retry-After when present. See OpenAI’s 429 troubleshooting guide.
- Rate or token limit: Compare the response with the relevant model or endpoint limit, including any short-window burst behavior.
- Concurrency limit: Inspect active sessions and the provider’s plan-specific error code; ElevenLabs documents
too_many_concurrent_requestsfor this case. - Backend capacity: A service-busy response may reflect provider load rather than your quota; ElevenLabs’
system_busyand Azure’s standard-voice regional capacity guidance illustrate this distinction. - Billing or usage cap: Check account balance and organization usage settings before retrying; repeated requests will not resolve a hard cap.
- Payload rejection: Check request size or duration against the endpoint’s per-operation limit instead of treating every failure as a throughput problem.
Control bursts without evading provider limits
When your traffic is spiky, smooth arrivals with a queue or token bucket and place an explicit bound on simultaneous sessions. For retryable throttling, use exponential backoff with jitter, obey any supplied retry delay, and make retries idempotent where possible so a timeout or duplicate delivery does not create unintended work. Log the provider, model, region, project, status and error code, retry-after value, and request or session size. This gives you evidence to distinguish a traffic-shaping problem from a limit that needs a legitimate increase.
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Do not spread traffic across extra accounts or projects to get around a provider’s restriction. In Deepgram’s case, the published terms explicitly reject using projects to bypass concurrency limits. More generally, compare an approved quota increase with the engineering cost of pacing and queueing, or choose a service whose published capacity model fits the workload.
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