LecSync vs Deepgram Flux: Live Captions vs Voice-Agent STT

Deepgram Flux is a streaming speech-to-text model built for voice agents: turn detection, barge-in handling, and ultra-low end-of-turn latency on wss://api.deepgram.com/v2/listen. On Deepgram’s pricing page (checked October 28, 2026), Flux English Pay As You Go is a limited-time promotional $0.0065 per audio minute (list $0.0077), and Flux Multilingual is $0.0078 per minute. Growth plan promos list $0.0057/min (EN) and $0.0068/min (multilingual).

The LecSync Realtime Speech API is a managed WebSocket for live meeting and lecture captions: preview and final text, translation between any two of 60 languages, a speaker and audio-aligned timestamps on every final segment, and running minutes. It costs $0.006 per audio minute ($0.36 per hour) with those features included.

Figures below were checked on October 28, 2026 against Deepgram pricing, the Flux quickstart, models & languages overview, language prompting, and the listen-flux API reference. This post is separate from the earlier LecSync vs Deepgram Nova comparison: Flux is a different model family, endpoint, and price row.

What is Deepgram Flux vs a realtime caption API?

Deepgram Flux is a conversational streaming STT SKU: model-native end-of-turn detection, EagerEndOfTurn for early LLM replies, turn-based transcripts, and word-level timestamps, aimed at voice agents and phone assistants. A realtime caption API such as LecSync keeps one session open for live bilingual captions, speakers and minutes while people are still talking — including lecture and meeting feeds where the product is readable captions, not agent turn control.

The short answer

If you are building a turn-based voice agent and need Deepgram’s end-of-turn events (~260 ms EOT on Flux docs) plus Nova-3-level accuracy claims on /v2/listen, Flux is the SKU Deepgram recommends for that job. Flux English promo PAYG sits near LecSync’s minute price; Flux Multilingual PAYG is higher.

If you need live bilingual captions + speakers + minutes on one flat minute bill, LecSync is the closer product. Flux Multilingual recognizes up to 10 languages in one conversation; it does not publish live any-to-any text translation or a live digest on the same socket the way LecSync does.

How each API works

LecSync. Your server calls POST https://api.lecsync.com/v1/realtime/connect with the audio format, a language pair and the features you want, then streams 16 kHz mono PCM. Preview text arrives while someone is still talking; a final segment settles once the sentence confirms. Translations share the segment ID. With speakers: true, each final carries a speaker and startMs/endMs on the recording clock. With digest: true, minutes arrive section by section. The first word shows up about 0.28 seconds after speech starts; translation adds roughly 88 ms. Seven gateway regions (dal, jp3, kc, nj, ru2, ru3, uk) keep audio near the capture point; backlog is capped at 2 seconds.

Deepgram Flux. Connect to wss://api.deepgram.com/v2/listen with model=flux-general-en or flux-general-multi (Flux will not work on /v1/listen). Stream PCM (linear16 @ 16 kHz recommended; ~80 ms chunks). The model emits turn events (EndOfTurn, optional EagerEndOfTurn / TurnResumed), word timestamps, and turn-structured transcripts. Configurable eot_threshold, eager_eot_threshold, and eot_timeout_ms tune how aggressively turns close. Multilingual Flux covers English, Spanish, French, German, Hindi, Russian, Portuguese, Japanese, Italian and Dutch, with optional language_hint. Deepgram’s models overview positions Flux for real-time agents; Nova-3 for meetings, multi-speaker captioning and noisy/far-field audio. Streaming add-ons on the pricing page (keyterm, redaction, entity detection, speaker diarization) are billed separately when you use them.

Pricing converted to dollars per hour (Calculated)

Minute math (Calculated): Flux EN promo → 1000 hours ≈ $390; Flux Multi PAYG → ≈ $468; Flux EN list → ≈ $462. LecSync stays $0.006/min whether translation and speakers are on or off → 1000 hours = $360. Growth Flux EN promo can undercut LecSync slightly on raw STT ($342 / 1000h Estimated) before you add MT, live speakers for meetings, or minutes yourself.

Side-by-side facts (checked October 28, 2026)

What 1,000 hours cost (Calculated)

Flux wins when the product is a voice agent that must know when the user stopped talking. LecSync wins when the product is a live bilingual caption feed with speakers and minutes. For flat-vs-add-on math, see what 1,000 hours cost once translation, speakers and summaries are added. For stitching your own STT + MT, see built-in translation vs a DIY pipeline. For the earlier Nova-oriented Deepgram write-up, see LecSync vs Deepgram.

When Deepgram Flux is the better pick

• Voice agents and phone bots that need model-native end-of-turn, EagerEndOfTurn, and barge-in on /v2/listen.
• Sub-second turn control — Flux docs cite ~260 ms end-of-turn detection with tunable thresholds.
• English-only agent pipelines at the promotional $0.0065/min PAYG (or Growth $0.0057/min) when you only need STT + turns.
• Ten-language conversational STT on flux-general-multi with language_hint, without needing caption MT.
• Deepgram ecosystem — same account credits as Nova, $200 free Pay As You Go credit (pricing FAQ), EU endpoint options.

When LecSync fits better

• Translated live captions on one socket — any pair of 60 languages, each translation tied to its segment.
• Speakers and recording-aligned timestamps during the live stream — meeting client with speakers and timestamps.
• Live minutes while the session runs (digest: true).
• Predictable minute billing at $0.36 an hour with no separate translation SKU and no turn-agent wiring required for captions.
• Classroom / mixed-language lecture feeds where captions must keep up as the speaker switches languages beyond Flux’s 10-language set.

Category winners

FAQ

Is Deepgram Flux the same as Nova-3 streaming?

No. Flux uses /v2/listen and models flux-general-en / flux-general-multi, with built-in turn detection for agents. Nova-3 remains Deepgram’s general-purpose ASR for meetings and captioning. Pricing lists them as separate streaming rows. Our earlier Nova-oriented comparison is LecSync vs Deepgram.

Does Flux include live multilingual text translation?

Flux Multilingual recognizes speech in up to 10 languages inside one conversation. Public Flux docs describe turn events and transcripts, not live any-to-any text MT into an arbitrary target language on the same socket. That caption path is a LecSync feature.

How does Flux pricing compare to LecSync at 1,000 hours?

Calculated from published $/min: LecSync ≈ $360. Flux English PAYG promo ≈ $390; Flux Multilingual PAYG ≈ $468; Flux English Growth promo ≈ $342. Promo rates are labeled limited-time on Deepgram’s pricing page — budget with the struck-through list rates if the promo ends.

Does Flux replace speaker diarization for meetings?

Flux optimizes turn-taking for one conversational agent loop. Deepgram’s models overview still recommends Nova-3 for multi-speaker meetings and captioning. Streaming speaker diarization appears as a priced add-on ($0.0020/min PAYG) on the pricing page — confirm on current docs before assuming meeting-style labels on Flux.

Can I mix both?

Yes. Some teams run Flux (or Nova-3) inside a voice-agent stack and LecSync for the live classroom or meeting caption feed with translation, speakers and digest.

Next step

Open the LecSync Realtime Speech API docs, create a connect session, and stream three seconds of silence to see preview and final segments on one socket — translation, speakers and digest included at $0.006 per audio minute.

curl -X POST "https://api.lecsync.com/v1/realtime/connect" \
  -H "Authorization: Bearer $LECSYNC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"audio":{"encoding":"pcm_s16le","sampleRate":16000,"channels":1},"transcribe":{"languages":["en"]},"store":false}'