nvoken Python SDK

An Invocation is one durable turn by a deliberately created, tenant-scoped Agent. An Agent binds your agent_key to one App-owned, versioned Agent Definition; a Session is one conversation with that Agent.

The package has three deliberate levels:

• Agent is the ordinary workflow facade: text, run, invoke, stream, and locally serialized bound Sessions.
• Client and InvocationHandle expose durable operations, transcript drains, provider-key lifecycle, iterators, configurable waits, and resumable streams.
• nvoken_generated is the complete generated Runtime transport and raw escape hatch.

python -m pip install nvoken
NVOKEN_BASE_URL=http://localhost:8080 NVOKEN_API_KEY=... \
  python examples/quickstart.py

The async facade provides durable handles, replay-safe retries, typed errors, cursor iterators, resumable SSE, composed result reads (result, list_messages, output_text), and callback verification. Session-scoped messages use Client.list_session_messages.

List or read the Agent record without admitting work:

agents = await client.list_agents(agent_key="support")
record = await client.get_agent(agents.items[0].id)

AgentResource is that record: tenant, key, display name, Definition binding, optional revision pin, lifecycle timestamps, and archive state. Agent is the object that runs its turns, and it corresponds to the same row — declare one from the keys you already own and it creates its record on first use:

agent = client.agent(AgentOptions(
    tenant_key=user_id,
    agent_key="support",
    definition_key="support",   # the Definition this instance follows
    tools=(lookup_order,),      # this process's handlers; never on the server
))

An Agent's identity and configuration live on the server; its tool handlers are supplied by whichever process runs the turn. await agent.ensure() creates the record at a moment you choose instead of on first use, and never mutates: the same keys and Definition resolve onto what exists, a different Definition is agent_key_conflict, an archived record is agent_archived, and a declared pinned_revision the record does not follow is refused. agent.resource and agent.id report the record once it is known, and agent.with_tools() attaches handlers to an Agent read back from the server.

Opt into the fixed guarded public-web reader with fetch_tool():

from nvoken import AgentDefinition, AgentOptions, Model, fetch_tool

definition = await client.create_agent_definition(AgentDefinition(
    definition_key="research",
    name="Research",
    instructions="Use nvoken_fetch for public URLs, then summarize the source.",
    model=Model(provider="anthropic", id="claude-sonnet-5"),
    tools=(fetch_tool(),),
))
options = AgentOptions(agent_key="research", definition_key=definition.definition_key)

The Runtime accepts only {"name":"nvoken_fetch","mode":"builtin"}. It owns public-address checks, up to five guarded redirects, one transient retry, HTML-to-Markdown conversion, and the ten-second and 64 KiB limits. Run python examples/fetch.py to summarize NVOKEN_FETCH_URL.

Use an Agent for the common path:

agent = client.agent(AgentOptions(
    agent_key="support",
    definition_key="support",
))

print(await agent.text("Why was I charged twice?"))
continued = agent.session(session_key="customer-123")
print(await continued.text("What should I do next?"))

A bound Session serializes admission only within that local binding. The Runtime remains authoritative across processes and rejects a second nonterminal turn. Agent operations dispatch configured host-tool handlers. If a waiting call has no handler, the Agent cancels before raising MissingToolHandlerError by default; set InvocationOptions(leave_waiting_on_missing_handler=True) only when another worker deliberately owns it. NoOutputTextError.result_kind distinguishes structured, tool-only, and empty completions.

For an intentional replace/regenerate action, use a new idempotency key and the typed option:

handle = await agent.invoke(
    "Try that answer again.",
    options=InvocationOptions(
        idempotency_key="customer-123:regenerate-2",
        if_active="supersede",
        session_key="customer-123",
    ),
)

Omission or "reject" preserves the default conflict response. Low-level callers set the same policy on InvokeRequest.if_active.

if_active="interrupt" is the keep-the-work variant: the active Invocation stops at its next execution seam and settles completed with stop_reason "interrupted", so the replacement turn builds on what it already produced. await handle.interrupt() asks for the same graceful stop without admitting a replacement, and Invocation.stop_reason names why any turn ended.

A turn can also stop without ending: "incomplete" means the Runtime enforced a budget at a seam, with stop_reason naming which one. It is terminal — the wait helpers stop there — and its work is kept, so treat it as an unfinished answer rather than an error. SessionMessage.phase says which assistant message was the reply: "final_answer" on the one that ended a completed turn, "commentary" on everything else, so an incomplete turn has none.

InvocationOptions(timeout=...) is one overall local deadline. Cancelling the calling task still raises native asyncio.CancelledError; it does not imply a durable Runtime cancellation. Call handle.cancel() when that is intended.

Recovery reads accept a status union, and a known Invocation can stream only durable frames:

page = await client.list_invocations(
    status=["queued", "running", "waiting"],
)
async for event in handle.events(deltas=False):
    ...

Equivalent status sets share cursor identity regardless of input order. Session get/list models expose typed nullable usage, computed from durable Invocation usage as a convenience estimate rather than a billing ledger.

Child Invocations

Record the exact ToolCall that caused another turn, and use normal Session retention when the child's transcript is temporary:

from nvoken import InvocationTrigger, InvokeRequest, SessionOptions, SessionRetention

request = InvokeRequest(
    agent_key="researcher",
    input="Investigate this branch",
    triggered_by=InvocationTrigger(
        type="tool_call",
        parent_invocation_id=parent.id,
        tool_call_id=call.id,
    ),
    session_options=SessionOptions(
        retention=SessionRetention(ttl_seconds=3600),
    ),
)

Pass parent_invocation_id to list_invocations: an Invocation ID selects its direct children, the literal "null" selects top-level Invocations, and omission keeps the unfiltered collection. Lineage does not propagate cancellation, budgets, results, or lifecycle state.

Install restart-stable compaction on a new or existing Session:

from nvoken import ContextCompaction, SessionOptions

request = InvokeRequest(
    agent_key="support",
    session_key="support:123",
    session_options=SessionOptions(
        compaction=ContextCompaction(trigger_tokens="auto"),
    ),
    input="hello",
)

Use an integer trigger and optional same-provider model for explicit policy. A Session without a policy accepts late opt-in; once installed, the policy is immutable. Supplied options on an existing Session must equal stored values or admission returns session_options_conflict.

Summary usage appears in Session usage rather than Invocation usage. Read applied and fell-through diagnostics with client.list_session_compactions(session_id).

InvocationOptions.metadata correlates a turn with your own records from the Agent binding. It is part of the admitted input, so it is immutable and material to idempotency: a replay carrying different metadata conflicts rather than updating it. That is why it is per-call rather than an AgentOptions default.

Pass a stored or one-turn provider key directly through InvokeRequest:

request = InvokeRequest(
    agent_key="support",
    input="hello",
    provider_keys=(
        ProviderKeySelection(
            provider="openai",
            source="caller_ephemeral",
            api_key=provider_key,
        ),
    ),
)

Stored sources are app_byok, tenant_byok, and platform and do not accept an api_key. Client.stream_session(session_id, reducer, consume) follows the Session until its task is cancelled; a terminal turn does not end the Session stream. For catch-up reads, use get_transcript_page when checkpointing each page or drain_transcript to consume one fixed cut.

Discover models through the same async facade:

catalog = await client.list_models(provider="openai")
selected = await client.get_model(
    Model(provider="openai", id=catalog.items[0].id)
)
print(selected.cataloged, selected.pricing.status)

The list is curated discovery metadata, not proof of provider-account access. Exact inspection also accepts uncataloged IDs.

Set an explicit portable temperature on the Agent Definition or a safe per-turn override:

from nvoken import AgentDefinitionOverrides, InvokeRequest, Model, Sampling

request = InvokeRequest(
    agent_key="support",
    input="hello",
    overrides=AgentDefinitionOverrides(
        model=Model(provider="anthropic", id="claude-haiku-4-5"),
        sampling=Sampling(temperature=0),
    ),
)

Omit sampling to preserve the provider default. Check selected.controls.sampling.temperature first; missing controls are unknown, and unsupported or unknown selections fail before durable admission. The portable range is [0,1]. top_p and stop sequences are intentionally absent; limits.max_output_tokens is the output guardrail.

Reasoning is typed and fail closed:

from nvoken import AgentDefinitionOverrides, InvokeRequest, Model, Reasoning

request = InvokeRequest(
    agent_key="support",
    input="hello",
    overrides=AgentDefinitionOverrides(
        model=Model(provider="anthropic", id="claude-opus-5"),
        reasoning=Reasoning(effort="high"),
    ),
)

Check selected.controls.reasoning first. budget_tokens requires a larger explicit limits.max_output_tokens. Omission preserves provider defaults; unsupported values and combinations are rejected without aliasing. OpenAI reasoning remains unavailable until its complete continuation representation is durable.

Structured-output schema preflight

Client.invoke and Agent operations call preflight_output_schema(schema) before transport when InvokeRequest.overrides.output_schema is present. Rejection is an NvokenError with code schema_preflight_failed; its safe details contain the portable issue code, RFC 6901 path, and optional keyword. A successful local check means eligible for admission. Generated APIs reached through client.raw() still rely on the authoritative Runtime check.

Define and instantiate an Agent

Every turn runs against an App-owned, versioned Agent Definition. Create a tenant-scoped Agent instance that binds to the template before admitting work:

resource = await client.create_agent_definition(AgentDefinition(
    definition_key="support",
    name="Support",
    instructions="Help with billing questions.",
    model=Model(provider="anthropic", id="claude-sonnet-5"),
))
agent = client.agent(AgentOptions(
    agent_key="support",
    definition_key=resource.definition_key,
))

handle = await agent.invoke("Why was I charged twice?")

AgentDefinition is flat and matches the wire, and a read gives back the same fields plus id, revision, and timestamps, so a change is a read, a replace(), and a write:

from dataclasses import replace

current = await client.get_agent_definition(resource.id)
await client.update_agent_definition(
    current.id,
    replace(AgentDefinition.from_resource(current), instructions="Be concise."),
    expected_revision=current.revision,
)

An update replaces the whole resource, so send back everything you want kept; from_resource is what keeps it whole. expected_revision travels as If-Match, so a concurrent write fails rather than overwriting.

Both writes are ensure-shaped: restating what nvoken already holds publishes nothing and returns the current revision. So a deploy step that owns its definitions in source does not read anything first — sync_definitions() writes them all and reports what moved:

for synced in await client.sync_definitions(definitions):
    if synced.outcome != "unchanged":
        print(f"{synced.definition_key}: {synced.outcome}")

Each definition costs one call, or two when its contents differ: the create conflict names the resource to replace, so nothing has to be looked up. Do not compare a definition against what you read back to decide whether to write — nvoken canonicalizes one before comparing it, and a second copy of that rule in your code is free to disagree the first time either side gains a field. Write unconditionally and read the outcome.

Creating a Definition starts no turn. It has an immutable definition_key, a stable ID, and an increasing revision; get_agent_definition_revision() reads historical revisions. Updating a Definition does not rewrite an Agent's binding. An Agent or Session may pin a revision, while an Invocation may select one revision for that turn. Safe overrides cover model, sampling, reasoning, tool choice, limits, and output schema; they cannot expand tools, data access, memory authority, or instructions. Host tool handlers remain local to the SDK facade.

Record changing application state

Keep instructions static. Product state that changes between turns — a board snapshot, customer facts, the current policy — belongs in context:

answer = await agent.text(
    "Can I refund the duplicate charge?",
    InvocationOptions(
        session_key="ticket-483",
        context=(
            ContextItem(name="customer", tier="contextual", content="plan: pro"),
            ContextItem(
                name="refund-policy",
                tier="operator",
                content="Self-serve refunds cap at 50 USD",
            ),
        ),
    ),
)

A name is a stable identity. Send it once and nvoken records it as a leading message the model reads as app-customer; omit that reserved prefix here. Send the same name again only when its value changes — a byte-identical resend is accepted but adds no message, so a stateless host may resend its whole snapshot every turn and get the same transcript as a host that tracks changes.

Use contextual for conversation-adjacent facts and operator for policy or other application-authoritative state. Context is Session history, not an Agent Definition field: it never changes definition_id, and later turns keep sending it to the model even when you omit it. That is what keeps the prompt prefix stable enough for provider caching, which rewriting the same state into instructions would break on every turn.

The list is order-sensitive and part of idempotency, so a replay that reorders or edits an item conflicts rather than updating it. A request accepts at most eight items, 8 KiB per item, and 16 KiB in total; the SDK checks all three before the request leaves the process. A Session may accumulate at most 16 distinct names, which only the service can check. Retire a name by superseding it with a short current value such as "ticket: closed".

Remote MCP tools

Use the handwritten declaration for discovery. Store the same declaration on the Agent Definition, then pass only its one-turn secret headers at admission:

server = MCPServer(
    name="support",
    url="https://mcp.example.com/rpc",
    allowed_tools=("lookup_order",),
    timeouts=MCPTimeouts(discovery_seconds=10, call_seconds=30),
)
headers = {"Authorization": f"Bearer {mcp_token}"}

catalog = await client.list_mcp_tools(server, headers)
request = InvokeRequest(
    agent_key="support",
    input="hello",
    mcp_server_headers=(MCPServerHeaders(name="support", headers=headers),),
)

The declaration carries no secrets. An Agent Definition may be reused across turns, so authentication headers travel per Invocation in mcp_server_headers, keyed to the server name. They are hidden from dataclass representation, are one-Invocation secret material, and never appear in durable Agent Definitions or public recovery surfaces.

Callback tools

A callback tool runs on an HTTPS endpoint nvoken posts to. Verify the signed delivery with verify_callback, then answer with one of two replies. callback_result(content, is_error=False) settles the ToolCall inline and the turn resumes as soon as nvoken records the reply. acknowledge_callback() returns 202 with no body instead: it accepts the delivery without settling the call, for work that will outlive this tool's reply deadline — its declared timeout_seconds, or the App's default when it declares none. Settle it later with client.submit_tool_results, reusing the delivery's ToolCall ID.

Every delivery names its tool inside the signed body, so one endpoint can serve several tools: dispatch on verified.tool_name rather than on a path suffix nothing signs.

Acknowledging trades away the fail-loud guarantee. nvoken marks an unacknowledged delivery failed once its retries are exhausted, so the turn always moves on. An acknowledged call instead waits under your responsibility, bounded only by the Invocation's limits.waiting_timeout_seconds. Acknowledge only when something durable will settle the call. Such a call appears in a waiting Invocation's pending calls the same way a host call does, so answerable_tool_calls includes it. host_tool_calls is the narrower set you must run yourself — answerable and mode host — and an Agent dispatches exactly that, whatever its own definition declares.

A callback endpoint, whole

verify_callback is the signature. Around it every receiver writes the same key table, the same deduplication, and the same reply discipline — CallbackReceiver is that, so you write the tools:

from nvoken import CallbackReceiver, DeliverySigningKey, callback_result


async def open_ticket(delivery):
    board = delivery.authorization_context.get("board")
    return callback_result(await create_ticket(board, delivery.envelope["input"]))


receiver = CallbackReceiver(
    # Two entries span a rotation: nvoken mints the next version while still
    # signing with the current one.
    keys=[
        DeliverySigningKey(key_id=KEY_ID, version=2, secret=SECRET),
        DeliverySigningKey(key_id=KEY_ID, version=1, secret=PREVIOUS_SECRET),
    ],
    tools={"open_ticket": open_ticket},
    store=ticket_replies,
)


@app.post("/nvoken/callbacks")
async def callbacks(request):
    answered = await receiver.handle(dict(request.headers), await request.body())
    log.info("nvoken callback", extra={"outcome": answered.outcome, "reason": answered.reason})
    return Response(answered.reply.body, status_code=answered.reply.status)

handle never raises. Everything that can go wrong is a status nvoken understands, and outcome — settled, acknowledged, replayed, refused, failed — is what the status alone cannot tell you, with a stable reason token for the log line.

The statuses are decisions about whether nvoken tries again:

A failed tool is not a failed receiver: settle it with callback_result(reason, True) and the model can correct itself, where a 5xx only has nvoken deliver the same doomed call again.

store is a find-then-put_if_absent pair, in that order. find runs before your tool does, because delivery is at least once and re-running the tool repeats every effect it had; put_if_absent runs after, because two deliveries of one ToolCall can be in flight at once and only one reply may win. Omit store only when every tool on the endpoint is safe to run twice.

The key table is validated when the receiver is built: a non-positive version, a secret under 32 bytes, or the same (key_id, version) twice raises at startup rather than refusing a live delivery, where the refusal would be permanent.

Authorizing a delivery

Verification proves the delivery came from nvoken. It does not say what the work belongs to, and the tool input cannot either — the model wrote it. session_options.authorization_context is what you asserted when the Session was created, and it arrives inside the signed body as a sibling of nvoken:

{
  "nvoken": { "tool_name": "open_ticket", "tenant_key": "acme" },
  "authorization_context": { "board": "brd_9f21" },
  "input": { "board": "brd_9f21", "ticket": "A-42" }
}

Everything inside nvoken is a fact nvoken minted; this is a value you asserted and nvoken carried unchanged. Signing proves it reached you as recorded, not that it is true. Which gives the rule:

A value repeated in tool input may only agree with the authorization context, never establish it.

Checking that the two agree is reasonable. Reading the board out of input when the context is absent is not. Authorizing from the signed sibling is also what removes the per-delivery get_invocation a receiver otherwise needs to recover which of your objects the work is for.

Receiving signed deliveries is the long form, language-neutral.

Invocation webhooks

A turn that ends tells you so, without you holding a connection open to hear it. Ask for it when you start the turn:

invocation = await client.create_invocation(
    agent_key="support",
    input="Where is my order?",
    webhook=WebhookTarget(url="https://example.com/nvoken/webhooks"),
)

Omitting events selects all three. invocation.ended fires once when the turn reaches a terminal status; invocation.waiting fires when it needs a host tool run; invocation.budget_hold fires when a spending limit stopped it.

Receiving one is the same verification you already wrote for callbacks — the signature scheme is identical, and verify_webhook is the same code path with a different body check:

from nvoken import accept_webhook, retry_webhook, verify_webhook

delivery = verify_webhook(webhook_signing_key, headers, raw_body)
if delivery.supersedes(await last_applied_sequence(delivery.invocation_id)):
    await settle(delivery.invocation_id, delivery.envelope["invocation"], delivery.sequence)
return accept_webhook()

The key is the App's webhook-purpose signing key, not its callback key. A receiver serving both endpoints holds two, and must not try either against the other's deliveries.

Three rules make a receiver correct:

Fold by sequence, not by arrival. Delivery is at least once, so the same transition can arrive twice and a redelivery can land after a later one. Keep the highest sequence you have applied per Invocation and apply only what supersedes accepts. That is the deduplication too — a repeat carries a sequence you already applied — so nothing else is needed to make handling idempotent.

The payload is a pointer, not a copy. It carries status, stop_reason, failure_code, waiting_tool_call_ids, and credit_block, and deliberately nothing else: no transcript, no output text, no usage. Read get_invocation or get_invocation_result when you need more, so you are reconciling against the authoritative record rather than a staler copy of it.

Answer retry_webhook() when you could not record it. Any 5xx is redelivered, as are 408, 425, and 429. Every other non-2xx answer is permanent and that transition is never delivered again, so a 400 from a receiver that was merely busy is a settlement you silently lost.

Retries are bounded, so webhooks alone are not a settlement guarantee. client.list_ended_invocations is the backstop: it walks turns in the order they ended, so a delivery that never landed is one you still find.

WebhookReceiver is CallbackReceiver's twin — same key table, same reply discipline — for the endpoint that has more than one event:

receiver = WebhookReceiver(
    keys=[DeliverySigningKey(key_id=WEBHOOK_KEY_ID, version=1, secret=WEBHOOK_SECRET)],
    events={
        "invocation.ended": settle_in_one_transaction,
        "invocation.budget_hold": alert_on_budget_hold,
    },
)

A handler that returns answers 200; one that raises answers 503 and nvoken delivers again. An event you subscribed to but registered no handler for answers 200 with outcome ignored — retrying it would only spend nvoken's bounded attempts reaching the same absent handler.

The sequence fold stays yours, deliberately: the compare and the write have to happen in the same transaction as the state they guard, and the receiver cannot open it. Call delivery.supersedes(applied) inside yours, and record nothing when it says no — a superseded delivery is still a delivery, and still answers 200.

Browser-direct access

Your page can talk to nvoken itself, with no server of yours in the path. Mint a short-lived grant in backend code and hand the browser that:

token = mint_client_token(
    client_key_seed,
    ClientTokenClaims(
        app_id=app_id,
        key_id=client_key_id,
        subject=user.id,          # from your session, never from the request
        tenant_key=user.workspace_id,
        agent_key="support",
        operations=["create_invocation", "get_session_transcript"],
        lifetime=timedelta(minutes=10),
    ),
)

Signing needs Ed25519, which the standard library does not provide, so install nvoken[client-tokens] for it.

nvoken client-key generate <app-id> --name web produces the keypair and registers its public half in one step. The private seed is the App's browser authority — whoever holds it can mint a grant for any end user — so it belongs in backend configuration and never in a bundle.

Three things are worth deciding rather than defaulting. operations is required: nvoken reads an absent list as every operation a browser may perform, so this SDK refuses to spell "I did not think about scope" the same way as all_browser_operations(). session_id confines the token to one conversation, which a single-conversation UI should set. And a lifetime is capped at fifteen minutes, because short lifetimes are the whole safety story of a bearer token in a page.

Invocation webhooks stop being optional here. The browser holds the stream, so your backend never observes settlement any other way.

Acting for one tenant or one end user

An app-wide credential can reach every tenant in its App, so an id that arrives from the wrong place — a stale link, a mixed-up webhook, a tampered form field — is an id it can act on. Say the scope once instead of re-reading the resource before every call:

from nvoken import Scope

tenant = client.scoped(Scope(tenant_key="acme", user_key="user-7c1f"))
session = await tenant.get_session(session_id_from_the_request)

Anything outside the scope is reported as not_found, so a Session or Invocation belonging to somebody else cannot be read, cancelled, interrupted, forked, answered, or erased — and you learn nothing about whether the id exists. Writes take the same scope: an omitted tenant or user key in the body inherits it, and one naming somebody else is refused.

A scope may only narrow. A credential already bound to one tenant refuses a scope naming another with forbidden rather than silently returning nothing. The client it was derived from is unchanged, so the unscoped one keeps doing administrative reads. Browser tokens already carry their tenant and end user and neither need this nor may send it.