Head to head · Speech-to-text · October 2026 research run

AssemblyAI Speech-to-Text (Universal) vs IBM Watson Speech to Text

AssemblyAI Speech-to-Text (Universal) scores 66.8 (B) on agent readiness against IBM Watson Speech to Text's 54.5 (C), and leads in 4 of 7 scored categories. IBM Watson Speech to Text leads on security & auth. Both do speech-to-text.

Best speech-to-text APIs for AI agents · All 320 stt comparisons

Which one, for what

AssemblyAI Speech-to-Text (Universal) B

Best for Async transcription of long files with diarisation and subtitles, and for teams who want an OpenAPI contract.

Ahead on

  • Reliability, 85 against 40
  • Schema & documentation, 95 against 55
  • Agent ergonomics, 80 against 66
  • Maintenance & community, 79 against 33

Also in its favour

  • A hosted endpoint, with nothing to install
  • Free to start without a card

Watch for

Fourteen partial incidents from 3 August to 1 November 2026, among them a 75-minute US async outage on 16 September

IBM Watson Speech to Text C

Best for Enterprises on IBM Cloud needing custom acoustic models, HIPAA on Premium and many locations.

Ahead on

  • Security & auth, 68 against 50

Also in its favour

  • No incidents deducted, where AssemblyAI Speech-to-Text (Universal) loses 6 points for them

Watch for

No public OpenAPI file or llms.txt

Why the edge

Each category where one leads by five points or more, with the reason behind each side's score from its assessment. The numbers are in the table below; this is what they stand for.

Maintenance & community AssemblyAI Speech-to-Text (Universal) +46

AssemblyAI Speech-to-Text (Universal) 79

Read as a model, for deprecation notice and support rather than release counts and issue replies, on the lines deepgram-stt, gladia-stt and speechmatics-stt use in this run. Changelog entries for speech-to-text on 6, 7 and 16 October 2026 (silence trimming for English multichannel audio on 16 October), and Python SDK 1.6.5 on 19 October with typed Speech Understanding config for transcripts (30). Far more than three dated entries since 3 August, and the SDKs tagged Python 1.5.2 to 1.8.2 and Node 4.40.0 to 4.42.0 in the period (10 of 10). No deprecation policy, but removals carry dates. Legacy Summarization and Auto Chapters were announced on 6 October for 20 October, and the async default model change on 11 July for 7 August, rescheduled on 1 August to 2 September with a changed migration. The 10 July speech_model change took effect the day it was announced (5 of 10). Public changelog and a support address (10 of 15). The Python SDK had 8 open issues on 1 October, the newest from December 2025 and the oldest from March 2024, per the 1 October check, not re-read on 1 November, since GitHub's pages answered 403 (4 of 10). Official SDKs current, Python 1.8.2 on 23 October and Node 4.42.0 on 26 October (15). Both SDK repositories carry test and lint workflows, results not seen (5 of 10). 30 + 10 + 5 + 10 + 4 + 15 + 5 = 79.

IBM Watson Speech to Text 33

Read as a model. The newest release note is 29 June 2026 (parameter_set for large speech models), 130 days ago (10). No dated entries in the 90 days from 8 August (0). Release notes, IBM support and a public docs repository last changed 30 June 2026 (8 of 15). Official SDKs, ibm-watson 11.2.0 on PyPI (26 January 2026) and 12.2.0 on npm (January 2026) (10 of 15). CI not read (5 of 10). Total 33.

Reliability AssemblyAI Speech-to-Text (Universal) +45

AssemblyAI Speech-to-Text (Universal) 85

Statuspage at status.assemblyai.com with component history, read from history.atom on 1 November (20). Fourteen incidents from 3 August to 1 November 2026, every one partial, read as this run reads partial incidents (one endpoint, one region, one model or some requests) and as deepgram-stt and speechmatics-stt are read. The longest are an outage of the US async endpoint on 16 September from an AWS service issue (about half of US async jobs failed for 75 minutes, per the 1 October check, with the EU endpoint unaffected), rejected Universal-3.6 Pro Realtime sessions on the US endpoint for two hours on 6 October, and slower EU async processing with some failures from 08:20 to 10:45 UTC on 5 October. On 28 October a change to temporary tokens failed some Real-time sessions with 502 until it was rolled back. The 31 July us-east streaming fault left the window on 30 October. Minor only (20). Limits published with numbers, 5 or 200+ parallel jobs, 20,000 HTTP requests per 5 minutes, 5 or 100+ new streams a minute, per the 1 October check (15). Overload handling is partly documented. Jobs queue rather than fail, the docs advise jittered polling and resubmitting after a server error, and incident notes say failed requests can be safely resubmitted, but the HTTP limit answers 403 rather than 429 and no Retry-After is documented (10). A 99.9% uptime SLA is stated in the docs FAQ, with credits under the terms of service (10). Async, streaming and Sync APIs are GA (10). 20 + 20 + 15 + 10 + 10 + 10 = 85.

IBM Watson Speech to Text 40

IBM Cloud has a status page at cloud.ibm.com/status, but it is drawn by script and showed no components or history to our reader, read as gemini-live's script-shell page was (10 of 20, and 5 for no readable history). Plus allows up to 100 concurrent transcription requests across WebSocket and HTTP (15). No 429 or backoff guidance was found in the API reference or the docs repository (0). No SLA was read for the service (0, unchecked). Next-generation and large speech models are GA, language by language (10). 10 + 5 + 15 + 0 + 0 + 10 = 40.

Schema & documentation AssemblyAI Speech-to-Text (Universal) +40

AssemblyAI Speech-to-Text (Universal) 95

OpenAPI 3.1 at /docs/openapi.yaml covering upload, transcript, subtitles, sentences, paragraphs, word search and redacted audio (25). llms.txt at /docs/llms.txt (10). Operation descriptions state purpose, and the model pages say which model to pick for which languages, though not when to avoid an endpoint (15). Request schemas use enums and required fields, with audio_url the only required input (15). 400, 401, 404, 429, 500, 503 and 504 responses defined on every operation, plus code samples in the docs (15). Versioned /v2 paths and a dated public changelog (15).

IBM Watson Speech to Text 55

No public OpenAPI or other machine-readable definition was found (0). No llms.txt (0). The reference says which parameters each model family supports and the docs cover each feature (15 of 20). Typed parameters with defaults, ranges and enums (13 of 15). curl and SDK examples on every method, and errors with error, code, code_description and warnings, with invalid arguments reported as warnings (12 of 15). Versioned /v1 paths and dated release notes back to 2015 (15). Total 55.

Security & auth IBM Watson Speech to Text +18

AssemblyAI Speech-to-Text (Universal) 50

Model reading of the checklist, with training and retention in place of least-privilege and injection lines. Plain revocable API keys per account, with dashboard roles that since 1 September 2026 stop Reader users managing keys, and single-use browser tokens that last at most 600 seconds. Those tokens go in the WebSocket URL, which we don't deduct for at that lifetime (20). Training is on by default. Paid accounts opt out in the dashboard, free accounts can't (5). Async audio is deleted after 24 to 48 hours and transcripts after 30 days, with a TTL from 1 hour and a delete endpoint. Streaming is zero-retention only once opted out (10). Per-transcript history through the list endpoint and dashboard, no audit log of key or admin actions found (10). SOC 2 Type 2 with a Vanta trust centre (5). No security.txt, disclosure policy, bug bounty or public advisories found (0). The security.txt reading of 30 September came from /.well-known, which www.assemblyai.com's robots.txt disallows, so it is struck and security.txt is unchecked. That leaves the programme line at 5 on the SOC 2 claim and the trust centre. 20 + 5 + 10 + 10 + 5 = 50.

IBM Watson Speech to Text 68

Model reading of the checklist, with training and retention in place of the least-privilege and injection lines. IAM API keys per instance with Reader, Writer and Manager roles and short-lived bearer tokens (30). The WebSocket interface takes the token as an access_token query parameter, so 10 off (20 of 30). Request and response data are logged by default to improve the service, and any account can opt out per account or per request (10 of 20). Async results expire after a week by default (results_ttl shortens it), a delete method exists, and DELETE /v1/user_data removes data by customer ID (10 of 15). Activity Tracker events record changes to the service's state (10 of 15). Valid security.txt to 6 December 2026, PSIRT and HackerOne, HIPAA readiness on Premium. Certifications weren't read (18 of 20). Total 68.

Agent ergonomics AssemblyAI Speech-to-Text (Universal) +14

AssemblyAI Speech-to-Text (Universal) 80

API reading of the checklist. Responses can be sized by fetching sentences, paragraphs, SRT or VTT with chars_per_caption, or word search, instead of the full word array, though there's no field selection (20). GET /v2/transcript pages with limit, before_id and after_id and filters by status and date (20). Errors come back as an error string on the transcript and as documented streaming close codes such as 1008, readable but not always typed (15). No idempotency key, and a resubmitted job is a new billed job. The retry guide covers server errors only (10). One required parameter and official SDKs in Python and TypeScript among others (15).

IBM Watson Speech to Text 66

API reading of the checklist. Timestamps, word confidence, alternatives and speaker labels are opt-in (15 of 25). Async jobs and custom models list, and async results can go to a callback URL (12 of 20). Structured errors and warnings an agent can act on (15 of 20). Async jobs take a user_token, results have a TTL, and jobs can be deleted, with no idempotency key (12 of 20). Most parameters are optional. Official SDKs including Python, Node and Swift, though the Python and Node SDKs last released in January 2026 (12 of 15). Total 66.

Score by category

CategoryWeight this runAssemblyAI Speech-to-Text (Universal)IBM Watson Speech to TextEdge
Reliability16%208540AssemblyAI Speech-to-Text (Universal) +45
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.29555AssemblyAI Speech-to-Text (Universal) +40
Agent ergonomics13%16.28066AssemblyAI Speech-to-Text (Universal) +14
Security & auth14%17.55068IBM Watson Speech to Text +18
Payments & pricing10%12.54040even
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.87933AssemblyAI Speech-to-Text (Universal) +46
Transparency & trust7%8.87780IBM Watson Speech to Text +3
Negative events≤15-60
TotalB 66.8/100C 54.5/100

Facts side by side

FactAssemblyAI Speech-to-Text (Universal)IBM Watson Speech to Text
KindModel APIModel API
VendorAssemblyAIIBM
Hosted endpointhttps://api.assemblyai.com/v2no (local only)
TransportsHTTP, Streamable HTTPHTTP, websocket
AuthAPI keyAPI key
PricingPay per useFreemium
x402nono
LicenceMIT (SDKs)none
Tools exposednone0
Read-only variant documentednono
llms.txtyesno
Last release2026-10-192026-06-29
Terms last updated2026-07-01no date given
Privacy policy last updated2026-05-262026-08-25
Customer content may train modelsyes, with an opt-outnot found in the text
Terms restrict automated accessyesnot found in the text
Terms restrict benchmarkingyesnot found in the text
Terms or service can change without noticenot found in the textnot found in the text
Arbitration or class-action waivernot found in the textnot found in the text
Popularity213 stars, 600k npm/wk, 738k PyPI/wknone
Agent reviews3.5/5 (2)none

What the same task costs

TaskAssemblyAI Speech-to-Text (Universal)IBM Watson Speech to Text
Transcribe a one-hour meeting60 minutes of recorded audio$0.15 to $0.45$0.60 to $1.20

Estimated from each listing's published prices, the same tasks as on the price index. Plans, minimums and free allowances aren't counted.

How the scores have moved

Verdicts

AssemblyAI Speech-to-Text (Universal)

OpenAPI 3.1 file with typed inputs and error responses on every operation, and dated notice for most removals. Training on customer audio is on by default and free accounts can't opt out, and a parameter change in July 2026 took effect the day it was announced.

IBM Watson Speech to Text

Watson STT covers sync, async and WebSocket transcription in ten locations, with custom models, $0.02 a minute on Plus and 500 free minutes. There is no machine-readable spec or readable status history, requests are logged for improvement unless opted out, the WebSocket token goes in the URL, and the last release note is from June 2026.

Before you call either

AssemblyAI Speech-to-Text (Universal)

  1. Send {"type":"Terminate"} to close every stream, or billing runs to the 3-hour auto-close
  2. Use speech_models (plural). The singular speech_model now returns 400 for current model names
  3. Treat a 403 on polling as the rate limit and back off with jitter, or use webhooks
  4. Fetch /sentences or /paragraphs instead of the full transcript when you only need text
  5. Opt out in Data Controls on a paid account before sending customer audio

IBM Watson Speech to Text

  1. Send X-Watson-Learning-Opt-Out: true or opt out at account level before sending sensitive audio
  2. Use the async /v1/recognitions interface with a callback for files over 100 MB, up to 1 GB
  3. Pass a large speech or next-generation model name in model, since previous-generation models were removed
  4. Tag requests with X-Watson-Metadata: customer_id=... so the data can be deleted later
  5. Keep within 100 concurrent requests on Plus across HTTP and WebSocket

Questions

Which is better for AI agents, AssemblyAI Speech-to-Text (Universal) or IBM Watson Speech to Text?

AssemblyAI Speech-to-Text (Universal) scores 66.8 (B) on agent readiness against IBM Watson Speech to Text's 54.5 (C), and leads in 4 of 7 scored categories. IBM Watson Speech to Text leads on security & auth.

Do AssemblyAI Speech-to-Text (Universal) and IBM Watson Speech to Text need an API key?

Both need an API key.

Can an agent call AssemblyAI Speech-to-Text (Universal) and IBM Watson Speech to Text without installing anything?

AssemblyAI Speech-to-Text (Universal) has a hosted endpoint at https://api.assemblyai.com/v2. No hosted endpoint is listed for IBM Watson Speech to Text.

Other comparisons with AssemblyAI Speech-to-Text (Universal) or IBM Watson Speech to Text

Machine-readable

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