Files
LocalAI/docs/content/features/openai-realtime.md
Richard Palethorpe 49ef40a187 feat(classifier/VAD): support voice control on low power devices (#10804)
* feat(llama-cpp): route Score through the slot loop

Score previously bypassed the slot loop with a direct llama_decode: a
conflict guard aborted the whole process if scoring raced generation, the
config validator had to reject score alongside chat/completion/embeddings,
and every candidate re-decoded the full shared prompt.

Add SERVER_TASK_TYPE_SCORE to the (patched) upstream server so score tasks
are scheduled like any other slot work: generation and scoring serialize
naturally, the shared prompt is decoded once per call, and the slot's
prompt cache carries the conversation prefix across calls. Context
checkpoints at the score boundary and at the cache-divergence point keep
SWA/hybrid/recurrent models (e.g. LFM2.5) from re-prefilling the whole
prompt per candidate: warm-turn scoring on a 6-option set drops from ~8s
to ~0.5s on a desktop CPU.

The conflict guard and the validation split are removed; declaring score
with generation usecases on one config is now supported and shares the
slot cache.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* feat(realtime): classifier wire types and pipeline config

Wire types and YAML config for realtime classifier mode: sessions carry a
localai_classifier extension (options with canned replies/tool calls,
softmax threshold, normalization, history trimming, fallback modes, and a
deterministic wake-word address gate), mirrored by pipeline.classifier in
the model YAML and surfaced in the config-meta registry. The
localai.classifier.result server event reports the full score distribution
per turn.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* feat(realtime): classifier response flow

Classifier-mode responses: instead of autoregressive generation, each user
turn is prefill-scored against the option list (router.ScoreClassifier
prompt/candidate shapes over the Score primitive) and the winning option's
canned reply and tool call are emitted through the existing response
machinery. Below-threshold turns take the configured fallback (none /
canned reply / generate); empty transcripts and unaddressed turns (wake
word not mentioned) skip scoring entirely. The scoring probe defaults to
the latest user message only — small scorers echo canned replies from
prior turns back as the top option otherwise.

Built for hardware that can afford prompt processing but not decode: with
slot-based Score the option list stays KV-cached across turns, so a turn
costs roughly one forward pass over the new words.

session_update_error events now carry the validation cause instead of a
generic message.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* fix(realtime): bound the VAD tick's scan window and buffer retention

The VAD tick loop re-scanned the entire input buffer every 300ms and only
trimmed it on zero-segment ticks or commits. Audio that keeps producing
segments without a committing pause (steady noise a mic pipeline lets
through, music, continuous speech) grew the buffer toward the 100MB cap
with each tick rescanning all of it — O(n^2), measured at ~3.3ms of silero
per buffered second: past ~90s retained, ticks run back to back and pin
~4 cores until the stream stops.

Silero's recurrent state only carries a few hundred ms of context, so
rescanning old audio buys nothing. Clip the slice handed to the VAD to the
largest silence the commit test can need to measure (server_vad silence
window or the semantic eagerness fallback) plus a warm-up margin, and
rebase the returned segment times so every downstream consumer keeps
whole-buffer coordinates. An open turn whose clipped window is all silence
now commits (the silence outran the window) instead of being discarded as
no-speech. Independently, retain at most 90s of raw buffer, rebasing the
live-feed and EOU cursors on trim — this also bounds the previously
unbounded VAD-error path. Turn boundaries are otherwise unchanged: no
forced commits, no new coordinator states.

pipeline.turn_detection.vad_window_sec can widen the scan window; values
below the automatic floor are ignored. The tick body is extracted into
vadTick so specs can drive turn detection synchronously (same shape as
classifySoundWindow); the babble reproduction that pinned 4 cores now
plateaus under 10% of one core.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* fix(backend): let per-model threads override the global default

ModelOptions overrode a set per-model threads value with the app-level
--threads whenever the latter was non-zero — and WithThreads defaults it
to the physical core count, so it always was. The YAML threads: knob has
been dead config: a tiny VAD model could never opt down from the global
pool size.

SetDefaults already fills an unset per-model value from the app config,
which is the intended precedence; resolve threads through a helper that
honors it (explicit threads: 0 still means unset).

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* chore(gallery): single-thread the silero VAD

Silero is a ~2MB recurrent model with no exploitable graph parallelism:
measured per-call latency is identical at 1 and 10 ORT threads, while
every extra pool thread just spin-waits between the realtime loop's
frequent tiny inferences.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* docs(realtime): classifier mode, VAD scan window, threads precedence

Document the realtime classifier mode (options, threshold guidance,
wake-word address gate, empty-transcript handling), the VAD scan window
and 90s buffer retention (pipeline.turn_detection.vad_window_sec), the
per-model threads precedence, and the M3 classifier note in the realtime
state-machine design doc.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* perf(llama-cpp): score all candidates in one batched decode

One scoring call is now a single SERVER_TASK_TYPE_SCORE task: the slot
decodes the shared prefix (prompt + longest common candidate token
prefix) once, then forks one sequence per candidate off it
(metadata-only for the unified KV cache, copy-on-write for recurrent
state) and decodes every candidate's unique tail in one llama_decode.
Previously each candidate was its own task that restored the boundary
checkpoint and re-decoded its full tail sequentially, paying
per-candidate task and decode overhead.

The context reserves SERVER_SCORE_FORK_SEQS extra sequence ids (and
recurrent-state cells) beyond the parallel slots via the new
common_params::n_seq_score_forks. Forking requires the unified KV cache
(already this backend's default) since per-sequence streams would shrink
n_ctx_seq; an explicit kv_unified:false disables forking and Score calls
that need it fail cleanly. Candidates beyond the fork/output budget
decode in successive chunks.

Wire contract and scores are unchanged: per-token logprobs are stitched
from the shared region and the forked tails. Verified bitwise
deterministic call-to-call and independent of candidate order (no
cross-fork leakage via equal-length candidate swap); ranking matches the
per-candidate implementation on the drone battery (winner softmax
0.99996 vs 0.99997), and >16-candidate chunking, prefix-of-another and
empty candidates all pass.

Measured on a desktop CPU: warm /api/score calls 0.52s -> 0.23s; warm
realtime classifier turns 196-303ms. The 9-candidate drone turn decodes
~17 unique tail tokens in one batch instead of nine sequential ~220ms
checkpoint-restore tasks.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* fix(realtime): gate scoring capacity by model usecase

Reserve llama.cpp scoring slots only for models that explicitly declare the score usecase, while allowing score to coexist with chat and completion. Reject incompatible unified-KV settings and classifier activation on models without scoring capacity.

Propagate application defaults when resolving realtime and preload pipeline stages so unset thread counts are resolved consistently without overriding explicit model settings.

Assisted-by: Codex:gpt-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* fix(ci): honor APT mirrors in the prebuilt llama-cpp compile step

The builder-prebuilt path installs gcc-14 with apt directly and ignored
the APT_MIRROR/APT_PORTS_MIRROR build args the from-source path already
honors, so an ubuntu mirror outage broke every arm64 backend build. Pass
the args into the stage and run apt-mirror.sh (already in the build
context via COPY . /LocalAI) before the apt step.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* feat(realtime): classifier argument slots via constrained completion

Hybrid classify-then-complete: a classifier option's canned tool call can
declare typed argument slots (number | enum | string, with defaults and
prompt hints) referenced as "{{name}}" in the arguments template. When
the option wins, the slots are filled by a short grammar-constrained
completion that continues the exact scoring prompt — rendered by the same
cached ScoreClassifier, so the llama.cpp prompt cache is already warm —
with the chosen route JSON re-opened at the first slot field. A GBNF
grammar pins the field skeleton and frees only the values; temperature 0,
a couple dozen tokens at most (~300ms on a desktop CPU for two slots).

Slot declarations and hints ride the option descriptions in the shared
system prompt, informing scoring and the fill alike at no per-turn token
cost. The localai.classifier.result event carries the final arguments and
a fill_latency_ms. On inference failure the slots' defaults apply; a slot
without a default fails the response (or falls through with
fallback.mode: generate). Slot filling requires completion alongside
score in the scoring model's known_usecases.

Verified end-to-end on the Pi drone demo: "fly forward three meters" in
distance mode classifies forward and infers {"distance": 3, "units":
"meters"} in ~310ms, and the drone flies exactly 3 units.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* feat(realtime): splice filled slot values into classifier replies

A classifier option's spoken reply can now reference its tool's argument
slots ("Going forward {{distance}} {{units}}."): the values inferred by
the slot-fill completion — or the recovery defaults — are spliced into
the reply as plain text before it is emitted, so what the assistant says
confirms what it actually inferred. Placeholders without a value stay
literal, and options without slots are untouched.

FillToolArguments now returns the raw slot values alongside the spliced
arguments JSON to make the reply templating possible.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* fix(realtime): harden classifier slot completion

Reserve context for constrained slot filling, size completions from their encoded output, and encode enum grammar literals as valid JSON. Reject empty enum values and cover the failure modes with regression tests.

Assisted-by: Codex:gpt-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* feat(realtime): prewarm the classifier scoring prompt on registration

Swapping a session's classifier option list (a voice-switched command
mode, for instance) made the next turns pay a full re-prefill of the new
option-list prompt — measured 2.4s vs 0.3s warm on a desktop CPU, and
worse: on hybrid-memory models like LFM2.5, whose state cannot be
partially rewound (llama.cpp can only restore checkpoints), *every*
probe change re-prefilled from scratch whenever the last checkpoint
missed the probe boundary, so even same-list turns intermittently cost
full prefills.

Registering an option list (pipeline seed or session.update) now fires a
best-effort background prewarm: two throwaway scores with distinct
probes. The first prefills the new option-list prompt; the second,
diverging exactly where per-turn probe text starts, plants the backend's
rewind point (KV checkpoint) at the stable-prefix boundary that every
real turn reuses. The prewarm hides behind the canned mode-switch reply
— by the time it finishes speaking, the cache is warm. Idempotent per
option set, detached from the registering request's lifetime.

Measured on the drone demo (LFM2.5-1.2B, desktop CPU): first turn after
a mode switch 2374ms -> 340ms; intermittent same-list full prefills
(1.3-2.1s) all -> under 0.5s. For clients that swap lists frequently,
options: [parallel:2] on the scoring model additionally keeps one slot
per list via prefix-similarity routing (+26MB RSS, unified KV).

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* perf(llama-cpp): checkpoint scoring at the caller-declared stable prefix

Hybrid-memory models (LFM2.5 shortconv, Qwen3.5 deltanet — where new
small models are headed) cannot rewind their state, so any prompt-cache
reuse that needs a rewind falls back to a full re-prefill. For classifier
scoring that meant every probe change re-processed the whole option-list
prompt: the server's checkpoints were placed reactively (at wherever the
previous task happened to diverge), so a checkpoint past the next
divergence was erased rather than restored — measured as intermittent
2-10s turns on prompts with a 95%+ common prefix.

The classifier now computes the probe-invariant prompt prefix once (the
byte-wise common prefix of two synthetic probe renders) and declares its
length with every Score request; the server maps it to a token boundary
and forces a KV checkpoint exactly there on each score prefill. That
checkpoint sits at or before every future divergence under the same
option list, so it always survives and always restores — repeat scoring
costs probe+candidates regardless of how the probe changes.

Also:
- prewarm reruns on every option-list registration instead of memoizing
  per list: with boundary checkpoints a redundant rewarm costs two
  probe-sized decodes, while skipping one after a slot eviction (three
  lists sharing fewer slots evict in LRU cascades) silently moves a full
  re-prefill onto the user's next turn
- new llama.cpp backend option rs_seq:N exposes bounded recurrent-state
  rollback outside speculative decoding; measured impractical for
  deltanet-scale states (65GB for 64 snapshots on Qwen3.5-4B) but cheap
  insurance for small-state models
- docs: the multi-list recipe (parallel:N + sps:0.5 — the default slot
  similarity threshold funnels distinct lists onto one slot)

Measured on the drone demo (LFM2.5-1.2B scorer, desktop CPU), steady
state: every turn 285-421ms including mode switches, vs 2.4s post-switch
and intermittent 1.3-2.9s re-prefills before.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* fix(realtime): align classifier cache guidance

Document the single-score prewarm behavior and clean the vendored score patch formatting.

Assisted-by: Codex:gpt-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* fix(llama-cpp): guard score task for fork backends

TurboQuant and Bonsai reuse the primary gRPC server against llama.cpp forks that do not carry LocalAI's slot-based Score patches. Compile the Score integration only for the patched primary backend and return UNIMPLEMENTED from fork builds instead of referencing absent task types and common_params fields.

Assisted-by: Codex:gpt-5 [gh]
Signed-off-by: Richard Palethorpe <io@richiejp.com>

* fix(dev): generate gRPC code before commit lint

The coverage phase regenerates ignored protobuf bindings, but lint runs first and can fail against missing or stale output. Generate the pinned bindings before lint so the gate always type-checks the current schema.

Assisted-by: Codex:gpt-5
Signed-off-by: Richard Palethorpe <io@richiejp.com>

---------

Signed-off-by: Richard Palethorpe <io@richiejp.com>
2026-07-29 12:50:22 +02:00

32 KiB


title: "Realtime API" weight: 37

The realtime voice loop: VAD to STT to LLM to TTS, over WebSocket or WebRTC

LocalAI supports the OpenAI Realtime API which enables low-latency, multi-modal conversations (voice and text) over WebSocket.

To use the Realtime API, you need to configure a pipeline model that defines the components for Voice Activity Detection (VAD), Transcription (STT), Language Model (LLM), and Text-to-Speech (TTS).

Configuration

Create a model configuration file (e.g., gpt-realtime.yaml) in your models directory. For a complete reference of configuration options, see [Model Configuration]({{%relref "advanced/model-configuration" %}}).

name: gpt-realtime
pipeline:
  vad: silero-vad-ggml
  transcription: whisper-large-turbo
  llm: qwen3-4b
  tts: tts-1

This configuration links the following components:

  • vad: The Voice Activity Detection model (e.g., silero-vad-ggml) to detect when the user is speaking.
  • transcription: The Speech-to-Text model (e.g., whisper-large-turbo) to transcribe user audio.
  • llm: The Large Language Model (e.g., qwen3-4b) to generate responses.
  • tts: The Text-to-Speech model (e.g., tts-1) to synthesize the audio response.

Make sure all referenced models (silero-vad-ggml, whisper-large-turbo, qwen3-4b, tts-1) are also installed or defined in your LocalAI instance.

Streaming the pipeline

By default each stage runs to completion before the next begins: the whole utterance is transcribed, the full LLM reply is generated, then it is synthesized. Each stage can instead be streamed incrementally, which lowers the time-to-first-audio of a turn:

name: gpt-realtime
pipeline:
  vad: silero-vad-ggml
  transcription: whisper-large-turbo
  llm: qwen3-4b
  tts: tts-1
  streaming:
    llm: true             # stream LLM tokens as transcript deltas
    tts: true             # emit audio deltas per synthesized chunk
    transcription: true   # stream transcript text deltas of the user's speech
    clause_chunking: true # synthesize each clause as soon as it completes
  • streaming.tts: emit a response.output_audio.delta per audio chunk the TTS backend produces (requires a backend that supports streaming synthesis), instead of one delta for the whole utterance. Falls back to a single unary delta otherwise.
  • streaming.transcription: stream conversation.item.input_audio_transcription.delta events as the transcript is produced (requires a transcription backend that supports streaming).
  • streaming.llm: stream the LLM reply token-by-token as response.output_audio_transcript.delta events. The full reply is buffered and synthesized once it is complete - streamed as audio chunks when streaming.tts is enabled (and the TTS backend supports it), otherwise as a single unary delta. Reasoning/thinking is always stripped from the spoken transcript. Tool calls are supported while streaming when the LLM uses its tokenizer template (use_tokenizer_template: true): the backend's autoparser then delivers content and tool calls separately, so the spoken transcript never leaks tool-call tokens. Grammar-based function calling keeps the buffered path.
  • streaming.clause_chunking: instead of buffering the whole reply before TTS, split it into speakable clauses and synthesize each as soon as it completes, lowering the time-to-first-audio. The splitter is script-aware: it uses Unicode sentence segmentation (so it handles CJK 。!? with no whitespace), CJK clause punctuation (,、;:), and Thai/Lao spaces - it does not rely on whitespace sentence boundaries, so it works for languages such as Chinese, Japanese and Thai where the old per-sentence approach degraded to whole-message buffering. Requires streaming.llm; scripts that genuinely need a dictionary (e.g. Khmer, Burmese) simply stay buffered until a space or end-of-message. Off by default.

All streaming flags are off by default, so existing pipelines are unaffected.

Model warm-up (cold start)

Without warm-up the pipeline's models are loaded into memory only on first use within a session: the VAD on the first audio chunk, transcription at the first end-of-speech, the LLM on the first reply, and TTS on the first spoken output. On a cold session this staggers a load delay across those first few interactions - and a model that fails to load (missing weights, wrong backend, out of memory) only fails part-way through the first turn.

To avoid that, LocalAI warms the pipeline by default: it loads the VAD, transcription, LLM and TTS backends into memory before the session is announced, and the session start blocks until they are all ready. The loads run concurrently, so the wait is the slowest single model, not the sum. This means:

  • The first turn pays no cold-start cost - every backend is already resident.
  • Model-load errors surface at session start. If any stage fails to load, the session is not started and the client receives a model_load_error instead of session.created, so a broken pipeline fails fast and visibly rather than mid-call.

Set disable_warmup: true to restore the lazy "load on first use" behavior - session start no longer waits on loading and load errors surface on the first turn instead. Useful if you want idle sessions to avoid holding model memory they may never use:

name: gpt-realtime
pipeline:
  vad: silero-vad-ggml
  transcription: whisper-large-turbo
  llm: qwen3-4b
  tts: tts-1
  disable_warmup: true   # lazily load each model on first use instead of at session start

Pre-loading a pipeline on demand

Warm-up only fires when a realtime session opens. To load a pipeline into memory ahead of time - e.g. to warm it right after boot, or when running with disable_warmup: true - POST the model name to the admin-only /backend/load endpoint. For a pipeline model it loads every configured sub-model (VAD, transcription, LLM, TTS, sound_detection, voice_recognition) concurrently:

curl -X POST http://localhost:8080/backend/load \
  -H "Content-Type: application/json" \
  -d '{"model": "gpt-realtime"}'

The endpoint is not realtime-specific - it pre-loads any model. See [Backend Monitor]({{%relref "operations/backend-monitor" %}}) for the full request/response reference (it is the inverse of /backend/shutdown).

Turn detection

Turn detection decides when the user has finished speaking and the pipeline should respond. Two modes are supported, matching the OpenAI session schema:

  • server_vad (default): silence-based. The VAD model watches the audio and the turn commits after silence_duration_ms (default 500 ms) of silence. Simple and model-agnostic, but a fixed silence window must trade interrupting mid-sentence pauses against sluggish responses.
  • semantic_vad: model-driven. The transcription model itself signals end-of-utterance and the silence window becomes dynamic: short right after the model emits its end-of-utterance token, much longer when it does not - so pausing to think no longer gets cut off, while finished sentences get a fast response.

semantic_vad requires a transcription model that emits an end-of-utterance token over a cache-aware streaming decode - currently parakeet-cpp-realtime_eou_120m-v1 (the model is trained to distinguish "paused, expecting a reply" from "paused mid-thought"). The realtime pipeline feeds it the microphone audio live while the user speaks. With any other transcription backend the session degrades gracefully to silence-only detection using the eagerness timeout below (a warning is logged once). The model also emits a distinct end-of-backchannel token (<EOB>) for short acknowledgments like "uh-huh": those are transcribed but never treated as the user yielding the turn.

Sessions can opt in via session.update (turn_detection: {"type": "semantic_vad", "eagerness": "medium"}), or the pipeline can set a server-side default so clients need no changes:

name: gpt-realtime
pipeline:
  vad: silero-vad-ggml
  transcription: parakeet-cpp-realtime_eou_120m-v1
  llm: qwen3-4b
  tts: tts-1
  turn_detection:
    type: semantic_vad   # default for sessions on this model (server_vad if unset)
    eagerness: medium    # low | medium | high | auto (auto == medium)
    retranscribe: false  # see below
    # vad_window_sec: 6  # widen the per-tick VAD scan window (see below)

A client session.update still overrides type and eagerness per session.

VAD scan window: each turn-detection tick the VAD rescans only the most recent slice of buffered audio — sized automatically from the commit silence threshold (the server_vad silence window, or the semantic eagerness fallback) plus a warm-up margin, so long turns cost the same per tick as short ones. vad_window_sec widens the window if needed; values below the automatic floor are ignored. Buffered turn audio is retained for at most 90 s — a turn that genuinely never pauses (continuous speech or a noise source the VAD keeps classifying as speech) keeps only its most recent 90 s for the commit-time batch transcription (the semantic live stream is unaffected — it already consumed the audio incrementally).

Eagerness sets the fallback silence window used when no end-of-utterance token was seen (the model missed it, or the user genuinely trails off): low waits 8 s, medium/auto 4 s, high 2 s - the same max-timeout semantics OpenAI documents. After the token is seen, the turn commits on the next VAD tick (~300 ms).

Live captions: while the user speaks, semantic_vad streams conversation.item.input_audio_transcription.delta events under the item id the commit will later reuse, so clients can render the words as they are recognized. The completed event at commit carries the authoritative transcript and replaces the partial text (with retranscribe: true it may differ from the captions); a turn discarded before commit emits conversation.item.input_audio_transcription.failed so clients can retract its captions.

retranscribe (server-side only, semantic_vad only) cross-checks the streaming decode against a batch decode at commit time:

  • false (default): the transcript accumulated from the live stream is used as-is - the model runs once per utterance and the LLM starts immediately at commit.
  • true: the committed audio is re-transcribed offline. If the batch decode also ends with the end-of-utterance token the turn proceeds (using the batch transcript); if it does not, the commit is cancelled and the session keeps listening - treating the streaming token as a false positive. Both transcripts are compared and logged, which makes this mode a useful diagnostic for how well the streaming and batch decodes align, at the cost of one extra decode per turn.

Disabling thinking

For reasoning models, you can force the pipeline LLM's thinking off without editing the LLM model config:

pipeline:
  llm: qwen3-4b
  disable_thinking: true   # maps to enable_thinking=false for the realtime LLM

This is applied only to the realtime session's copy of the LLM config, so it does not affect other users of the same model. Leave it unset to use the LLM model config's own reasoning settings.

Conversation compaction (long sessions on CPU)

By default a realtime session feeds only the last max_history_items turns to the LLM; older turns are dropped and forgotten. On CPU, long calls also grow expensive as the prompt fills with verbatim history. Enable compaction to instead fold older turns into a rolling summary, so long calls stay cheap without losing earlier context.

Compaction works with two numbers:

  • max_history_items is the live window - the recent turns kept verbatim in the prompt.
  • compaction.trigger_items is the high-water mark - let the buffer grow to here, then summarize the overflow (everything above max_history_items) into a rolling memory and evict it. It must be greater than max_history_items; if it is not, it is clamped up.

The gap between the two controls how often summarization runs: a summary call fires roughly every (trigger_items - max_history_items) turns (here, about every 6 turns).

pipeline:
  max_history_items: 6        # live window - recent turns kept verbatim
  compaction:
    enabled: true
    trigger_items: 12         # summarize overflow back down to max_history_items
    summary_model: ""         # optional: a small model for the summary (CPU); default = pipeline LLM
    max_summary_tokens: 512

{{% notice tip %}} On CPU, set summary_model to a small, fast model so compaction never competes with the conversation LLM for compute. Left empty, the pipeline's own LLM produces the summary. {{% /notice %}}

Clients can also manage history directly via the now-supported conversation.item.delete, conversation.item.truncate, and input_audio_buffer.clear realtime events.

Classifier mode (LocalAI extension)

On hardware that can afford prompt processing but not token generation — a Raspberry Pi running a small LLM, for example — a realtime session can replace autoregressive generation with prefill-only classification: you register a fixed list of options, each user turn is scored against them with the Score primitive (a single forward pass, no decode), and the winning option's canned reply is spoken and/or its canned tool call is emitted. On llama-cpp, scoring runs through the same server slot the LLM uses, so the conversation prefix stays KV-cached across turns, and all options are scored together in one batched decode: the shared prefix (prompt plus the options' common token prefix) is processed once, then each option's unique tail rides a forked sequence in a single forward pass. A warm turn costs roughly one pass over the new words plus one small batch over the option tails, independent of the option count.

Enable it in the pipeline config:

name: drone-pi
pipeline:
  vad: silero-vad-sherpa
  transcription: parakeet-cpp-realtime_eou_120m-v1
  llm: lfm2.5-1.2b-instruct       # scores AND (if asked) generates
  tts: vits-piper-en_US-amy-sherpa
  classifier:
    enabled: true
    threshold: 0.85               # softmax floor the winner must clear (see note below)
    fallback:
      mode: reply                 # none | reply | generate
      reply: "Say again?"
    options:
      - id: up
        description: the user asks the drone to move or fly up/higher
        reply: Going up.
        tool:
          name: move
          arguments: {direction: up}
      - id: greeting
        description: the user greets the assistant
        reply: Hello, ready to fly.

Or per session / per response from the client (the field is additive — OpenAI clients simply never send it):

{"type": "session.update", "session": {"type": "realtime", "localai_classifier": {
  "enabled": true, "threshold": 0.85,
  "options": [{"id": "up", "description": "...", "reply": "Going up.",
               "tool": {"name": "move", "arguments": {"direction": "up"}}}],
  "fallback": {"mode": "reply", "reply": "Say again?"}
}}}

Like tools, the option list is replaced wholesale on each update. A response.create may carry its own localai_classifier to override the session for one response — {"enabled": false} runs normal generation once.

How a classified response behaves:

  • The winner's reply is emitted through the ordinary response events (spoken via TTS, or response.output_text.* in text-only mode), and its tool (if any) is emitted as a standard function_call item with exactly the configured arguments — the client executes it and reports back with conversation.item.create as usual. In classifier mode you typically should not send a follow-up response.create after the tool output: the canned reply already acknowledged the command, and the follow-up would classify a tool-output turn.
  • Every classified response also emits a localai.classifier.result event carrying the full softmax distribution, the chosen option id (empty when the fallback applied), the threshold, and the scoring latency — useful for visualizing confidence in a client UI.
  • A committed turn whose transcript is empty (the VAD fired on noise and the ASR heard no words) is never scored — an empty prompt produces a confidently arbitrary winner. The fallback applies directly: the result event carries an empty scores list, and generate mode falls through to generation.
  • Wake-word gating: set address: {names: ["drone"], mode: ignore} and the assistant only acts on turns that mention one of the names ("Drone go up", not just "go up"). The check is a deterministic case-insensitive whole-word match on the latest transcript — deliberately not model-based: scoring cannot detect a missing name (a 1.2B scorer rates "go up" as addressed with p≈1.0 even with a dedicated addressing stage), while a literal match is exact and free. Unaddressed turns skip scoring entirely (ambient conversation costs nothing) and emit a result event with empty scores and fallback: "not_addressed"; mode: ignore completes the response silently, mode: reply speaks reply.
  • When no option clears threshold, fallback.mode decides: none completes the response with no output, reply speaks the canned fallback reply, and generate falls through to normal autoregressive generation (slow on weak hardware, but always available since the same model config serves both paths). Set the threshold high: with the default raw normalization a confident in-list pick lands near 1.0, while an out-of-list request spreads its probability across the options — measured on a 1.2B scorer, in-list utterances scored ≥0.97 and out-of-list ones peaked around 0.8, so a floor of ~0.85 separates them. A low threshold (say 0.35) practically never falls back. Also keep each option's description narrowly scoped: a catch-all clause like "…or asks for help" turns that option into a magnet for every request the model cannot map, defeating the fallback.
  • Agentic follow-up turns (after a server-side assistant tool executes) always use generation — the option list describes user intents, not tool outputs.

Knobs that matter for latency and accuracy: keep option descriptions short (they all go into the scoring system prompt) and the option count small. By default only the latest user message is scored — earlier turns echo option names (the canned replies especially) and empirically make small scoring models re-choose the previous option regardless of the new command. history_items: N opts the trailing N conversation messages back in (role-labeled); only do that with a scorer large enough to weigh the context. normalization: mean divides each option's joint log-prob by its token count — useful when option ids have very different lengths. The scoring model needs a Go-side chat template (template.chat / template.chat_message); without one the scoring prompt falls back to a generic ChatML envelope, which may be off-distribution for the model. Use classifier.model to score on a different config than the pipeline LLM (rarely needed).

Argument slots (hybrid classify-then-complete)

A canned tool call can leave holes for the model to fill: declare slots on the option's tool and reference them as "{{name}}" in the arguments template. When the option wins, LocalAI runs a short grammar-constrained completion that continues the exact scoring prompt (so the llama.cpp prompt cache is already warm) with the chosen route JSON re-opened at the first slot — only the value tokens are free; everything else is pinned by the grammar. Number slots substitute unquoted, enum/string slots inside their quotes.

tool:
  name: move_drone
  arguments:
    direction: forward
    distance: "{{distance}}"
    units: "{{units}}"
  slots:
    - name: distance
      type: number            # number | enum | string
    - name: units
      type: enum
      values: [m, meters, ft, feet]
      default: m              # used if inference fails outright
      hint: assume m when the user gives no units

The option's spoken reply can reference the same placeholders — reply: "Going forward {{distance}} {{units}}." — and the filled values are spliced in as plain text before the reply is emitted, so what the assistant says confirms what it inferred. Reply placeholders are optional (one that names no slot stays literal).

Slot declarations (and hints) are appended to the option's description in the shared system prompt, so they also inform scoring and cost no extra per-turn tokens. The localai.classifier.result event carries the final arguments and a fill_latency_ms. On an inference failure the slots' defaults apply (and template the reply); if any slot lacks a default the response fails (or falls through to generation with fallback.mode: generate). Slot filling requires completion in the scoring model's known_usecases alongside score.

Registering an option list (pipeline seed or session.update) prewarms the scoring prompt in the background: one throwaway score prefills the option-list prompt and plants a state checkpoint exactly at the per-turn probe boundary. Every scoring call also declares that boundary (the probe-invariant prompt prefix) to the backend, which checkpoints there on each prefill — on hybrid/recurrent models (which cannot rewind their state arbitrarily, only restore checkpoints) this is what keeps every turn at probe-size cost instead of a full option-list re-prefill. A client that swaps option lists at runtime (e.g. voice-switched command modes) pays nothing on the first turn after a swap: the rewarm hides behind the acknowledgement reply, and it runs on every registration deliberately — if the list's slot was evicted, the rewarm is exactly the re-prefill the next turn would otherwise pay in the foreground. Swapping between several lists? Give the scoring model a slot per list and make the prefix routing selective: options: [parallel:3, sps:0.5] (the default slot-similarity threshold of 0.1 funnels different lists onto one slot — they share enough prompt structure to clear it).

The concrete scoring model must declare score in known_usecases. A single llama.cpp model can serve ordinary inference and classification concurrently by declaring multiple use cases, for example known_usecases: [chat, completion, score]; LocalAI reserves the scoring slots only when score is present. Scoring also requires the unified KV cache, which is enabled by default, so a score-enabled model cannot set kv_unified:false.

Transports

The Realtime API supports two transports: WebSocket and WebRTC.

WebSocket

Connect to the WebSocket endpoint:

ws://localhost:8080/v1/realtime?model=gpt-realtime

Audio is sent and received as raw PCM in the WebSocket messages, following the OpenAI Realtime API protocol.

WebRTC

The WebRTC transport enables browser-based voice conversations with lower latency. Connect by POSTing an SDP offer to the REST endpoint:

POST http://localhost:8080/v1/realtime?model=gpt-realtime
Content-Type: application/sdp

<SDP offer body>

The response contains the SDP answer to complete the WebRTC handshake.

Opus backend requirement

WebRTC uses the Opus audio codec for encoding and decoding audio on RTP tracks. The opus backend must be installed for WebRTC to work. Install it from the Backends page in the web UI, or from the backend gallery with the API:

curl -X POST http://localhost:8080/backends/apply \
  -H "Content-Type: application/json" \
  -d '{"id": "opus"}'

For a local binary installation, you can instead use the CLI:

local-ai backends install opus

Or set the EXTERNAL_GRPC_BACKENDS environment variable if running a local build:

EXTERNAL_GRPC_BACKENDS=opus:/path/to/backend/go/opus/opus

The opus backend is loaded automatically when a WebRTC session starts. It does not require any model configuration file - just the backend binary.

WebRTC behind Docker host networking or NAT

By default pion gathers a host ICE candidate for every local interface. Under Docker host networking that includes bridge addresses (docker0/veth, 172.x) that a remote browser cannot route to: the call typically connects on a good candidate and then drops a few seconds later when ICE consent checks fail on the unreachable ones. Two settings let you advertise only the reachable address:

# Advertise these IPs as the host ICE candidates (e.g. the host's LAN IP)
LOCALAI_WEBRTC_NAT_1TO1_IPS=192.168.1.10

# ...or restrict ICE gathering to specific interfaces
LOCALAI_WEBRTC_ICE_INTERFACES=eth0

{{% notice tip %}} For a browser on another LAN machine talking to LocalAI in a host-networked container, set LOCALAI_WEBRTC_NAT_1TO1_IPS to the host's LAN IP. This is the most reliable fix for WebRTC connections that establish and then drop. {{% /notice %}}

Protocol

The API follows the OpenAI Realtime API protocol for handling sessions, audio buffers, and conversation items.

Response modalities (text-only sessions)

By default a realtime session responds with audio plus a transcript. To make the model respond with text only, set the output modalities on either the session or an individual response:

{"type": "session.update", "session": {"output_modalities": ["text"]}}
{"type": "response.create", "response": {"output_modalities": ["text"]}}

output_modalities is the GA field name. For compatibility, LocalAI also accepts the legacy Realtime beta field name modalities as an alias (a lot of community sample code still sends modalities: ["text"]):

{"type": "session.update", "session": {"modalities": ["text"]}}

The GA output_modalities wins when both are present. A response-level value overrides the session-level one, and when neither is set the session falls back to ["audio"].

Gating a realtime pipeline with voice recognition

A pipeline realtime model can require speaker verification before it responds. Add a voice_recognition block under pipeline. When present, each committed utterance is verified against authorized speakers; unauthorized utterances are dropped before the LLM runs (no LLM call, no tool execution, no TTS). The session stays open.

The same block also drives two optional, independent behaviors: an authorization gate (enforce) and speaker surfacing/personalization (identity). Set enforce: false to keep recognizing the speaker without ever rejecting a turn.

name: my-realtime
pipeline:
  vad: silero-vad
  transcription: whisper
  llm: qwen
  tts: kokoro
  voice_recognition:
    model: speaker-recognition   # the speaker-recognition backend model
    mode: identify               # "identify" (registry) or "verify" (references)
    threshold: 0.25              # cosine distance; <= passes
    enforce: true                # authorization gate (default true)
    when: every                  # "every" (default) or "first"
    on_reject: drop_event        # "drop_event" (default) or "drop_silent"
    anti_spoofing: false         # optional liveness check (verify mode)

    # identify mode: authorized registry identities (multiple persons)
    allow:
      names: ["alice", "bob"]    # match registered speaker names
      labels: ["family"]         # OR any identity carrying this label
      # empty allow = any registered speaker within threshold passes

    # verify mode: reference speakers (multiple persons)
    references:
      - name: alice
        audio: /models/voices/alice.wav
      - name: bob
        audio: /models/voices/bob.wav

Identifying speakers without gating

To recognize who is speaking and surface it to the client and the LLM without ever rejecting a turn, set enforce: false and add an identity block. The identity block works with or without the gate; when it is set, the speaker is resolved on every turn even if when: first.

name: my-realtime
pipeline:
  vad: silero-vad
  transcription: whisper
  llm: qwen
  tts: kokoro
  voice_recognition:
    model: speaker-recognition
    mode: identify
    threshold: 0.25
    # Authorization gate. Defaults to enforcing (rejects unauthorized speakers).
    # Set enforce:false to identify the speaker WITHOUT rejecting anyone.
    enforce: false
    when: every
    # Surface the recognized speaker to the client and the LLM. Works with or
    # without enforce; when set, identity is resolved on every turn even if
    # when:first.
    identity:
      announce: true            # emit the conversation.item.speaker event
      announce_unknown: false   # also emit it when there is no confident match
      personalize: true         # tell the LLM who is speaking
      inject_name: true         # set the per-message OpenAI name field
      inject_system_note: true  # append a "current speaker" line to the system message
      note_unknown: false       # append a "speaker is unknown" note when unidentified
Field Meaning
model Speaker-recognition backend model name.
mode identify matches against speakers registered via /v1/voice/register; verify matches against the references audios.
threshold Maximum cosine distance that still counts as a match (default ~0.25).
enforce Authorization gate. true (or omitted) rejects unauthorized speakers (the gating behavior above). false resolves and surfaces the speaker without ever dropping a turn.
when every verifies each utterance; first verifies once then trusts the session. When an identity block is set, the speaker is still resolved on every turn even with first.
on_reject drop_event drops and emits a speaker_not_authorized error event; drop_silent drops quietly.
anti_spoofing Verify mode only: runs the backend liveness check (slower).
allow.names / allow.labels identify mode: which registry identities are authorized. Empty = any registered speaker.
references verify mode: authorized reference speakers; the utterance passes if it matches any.
identity.announce Emit the conversation.item.speaker event to the client (see below).
identity.announce_unknown Also emit that event when there is no confident match. By default the event is emitted only on a match.
identity.personalize Inform the LLM who is speaking.
identity.inject_name Set the per-message OpenAI name field on each user turn.
identity.inject_system_note Append a The current speaker is <Name>. line to the system message.
identity.note_unknown When unidentified, append The current speaker is unknown. (lets the model ask who it is talking to).

identify mode requires the voice registry (speakers registered through /v1/voice/register). verify mode needs no registry: reference audios are embedded once at model load.

The conversation.item.speaker event

When identity.announce is enabled, the server emits a conversation.item.speaker event after the user conversation item, naming the recognized speaker:

{
  "type": "conversation.item.speaker",
  "item_id": "item_abc",
  "speaker": { "name": "Jeremy", "id": "spk_1", "labels": { "role": "owner" }, "confidence": 92.0, "distance": 0.1, "matched": true }
}

confidence is a 0-100 score, distance is the cosine distance, and matched is true when a confident match was found. labels carries any labels attached to the registered speaker (identify mode); it is omitted when the speaker has none. The name and id fields are omitted when empty. By default the event is emitted only on a match; set identity.announce_unknown: true to also emit it (with matched: false) when no speaker is identified.

This event is a LocalAI extension to the OpenAI Realtime API and is server-emitted only. Standard OpenAI Realtime clients ignore event types they do not recognize, so enabling it is non-breaking.

Examples

  • Realtime voice assistant demo (Go): a minimal Go client for the Realtime (WebSocket) API with a full talk-back voice loop and an example tool call. Ships a docker compose setup that brings up a realtime-capable LocalAI for you.
  • Realtime voice assistant example (Python): thin-client architecture (Silero VAD on the client, heavy lifting on LocalAI), suited to running the client on a Raspberry Pi.