diff --git a/examples/devops/devops/agents/sre/tasks/review.py b/examples/devops/devops/agents/sre/tasks/review.py
index 5456e23..f8349f6 100644
--- a/examples/devops/devops/agents/sre/tasks/review.py
+++ b/examples/devops/devops/agents/sre/tasks/review.py
@@ -25,6 +25,7 @@
 from switchplane import Task
 from switchplane.agent_runtime import AgentContext
 from switchplane.llm import build_llm
+from switchplane.usage import estimate_text_tokens, llm_usage_from_response
 
 # -- Mock data generation ------------------------------------------------------
 #
@@ -337,18 +338,33 @@ def _strip_json_fences(text: str) -> str:
 class ReviewState(TypedDict):
     current: Any  # pd.DataFrame (not serializable, ephemeral task)
     previous: Any  # pd.DataFrame
+    rows_processed: int
+    estimated_raw_prompt_tokens: int
     analysis: dict | None
     formatted: str
     summary: dict | None
     report: str
 
 
-def _build_graph(llm) -> StateGraph:
+def _build_graph(llm, ctx: AgentContext, model: str) -> StateGraph:
     """Wire the review graph. 3 deterministic nodes, 1 LLM node."""
 
     def fetch_metrics(state: ReviewState) -> dict:
         current, previous = generate_metrics()
-        return {"current": current, "previous": previous}
+        raw_prompt = "\n\n".join(
+            [
+                "CURRENT WEEK RAW METRICS CSV:",
+                current.to_csv(index=False),
+                "PREVIOUS WEEK RAW METRICS CSV:",
+                previous.to_csv(index=False),
+            ]
+        )
+        return {
+            "current": current,
+            "previous": previous,
+            "rows_processed": len(current) + len(previous),
+            "estimated_raw_prompt_tokens": estimate_text_tokens(raw_prompt),
+        }
 
     def analyze_metrics(state: ReviewState) -> dict:
         result = analyze(state["current"], state["previous"])
@@ -356,11 +372,44 @@ def analyze_metrics(state: ReviewState) -> dict:
 
     async def summarize(state: ReviewState) -> dict:
         prompt = _ANALYSIS_PROMPT.format(formatted_data=state["formatted"])
-        response = await llm.ainvoke(
-            [
-                {"role": "system", "content": _SYSTEM_PROMPT},
-                {"role": "user", "content": prompt},
-            ]
+        messages = [
+            {"role": "system", "content": _SYSTEM_PROMPT},
+            {"role": "user", "content": prompt},
+        ]
+        response = await llm.ainvoke(messages)
+        usage = llm_usage_from_response(
+            response,
+            task_id=ctx.task_id,
+            model=model,
+            node_name="summarize",
+            fallback_prompt_text=f"{_SYSTEM_PROMPT}\n\n{prompt}",
+            fallback_completion_text=str(response.content),
+            estimated_raw_prompt_tokens=state["estimated_raw_prompt_tokens"],
+            metadata={
+                "deterministic_nodes": 3,
+                "llm_nodes": 1,
+                "rows_processed": state["rows_processed"],
+                "formatted_prompt_tokens_estimate": estimate_text_tokens(prompt),
+            },
+        )
+        ctx.record_llm_usage(
+            model=usage.model,
+            node_name=usage.node_name,
+            prompt_tokens=usage.prompt_tokens,
+            completion_tokens=usage.completion_tokens,
+            total_tokens=usage.total_tokens,
+            estimated_cost_usd=usage.estimated_cost_usd,
+            estimated_raw_prompt_tokens=usage.estimated_raw_prompt_tokens,
+            estimated_tokens_saved=usage.estimated_tokens_saved,
+            metadata=usage.metadata,
+        )
+        ctx.progress(
+            "LLM usage recorded",
+            prompt_tokens=usage.prompt_tokens,
+            completion_tokens=usage.completion_tokens,
+            total_tokens=usage.total_tokens,
+            estimated_cost_usd=usage.estimated_cost_usd,
+            estimated_tokens_saved=usage.estimated_tokens_saved,
         )
         try:
             summary = json.loads(_strip_json_fences(response.content))
@@ -431,16 +480,17 @@ async def run(self, ctx: AgentContext) -> None:
         ctx.progress(f"Starting ops review (model: {model})")
         ctx.progress("Generating mock NewRelic metrics (2 weeks, 5-min granularity)...")
 
-        graph = _build_graph(llm).compile()
-
         initial: ReviewState = {
             "current": None,
             "previous": None,
+            "rows_processed": 0,
+            "estimated_raw_prompt_tokens": 0,
             "analysis": None,
             "formatted": "",
             "summary": None,
             "report": "",
         }
 
+        graph = _build_graph(llm, ctx, model).compile()
         result = await graph.ainvoke(initial)
         ctx.complete(result["report"])
diff --git a/src/switchplane/__init__.py b/src/switchplane/__init__.py
index 79605a8..d6f2dbf 100644
--- a/src/switchplane/__init__.py
+++ b/src/switchplane/__init__.py
@@ -8,5 +8,6 @@
 from switchplane.app import Application
 from switchplane.shell import Shell
 from switchplane.task import Task, command
+from switchplane.usage import LLMUsageRecord
 
-__all__ = ["Application", "Field", "Shell", "Task", "command", "fmt"]
+__all__ = ["Application", "Field", "LLMUsageRecord", "Shell", "Task", "command", "fmt"]
diff --git a/src/switchplane/agent_runtime.py b/src/switchplane/agent_runtime.py
index 7916538..aaeb8ad 100644
--- a/src/switchplane/agent_runtime.py
+++ b/src/switchplane/agent_runtime.py
@@ -21,6 +21,7 @@
 
 from switchplane._util import MAX_MESSAGE_SIZE
 from switchplane.protocol import AgentCommand, AgentEvent
+from switchplane.usage import LLMUsageRecord, estimate_cost_usd
 
 _logger = structlog.get_logger()
 
@@ -243,6 +244,41 @@ def command_result(self, action: str, result: dict[str, Any]) -> None:
         """
         self.emit("task.command_result", {"action": action, "result": result})
 
+    def record_llm_usage(
+        self,
+        *,
+        model: str,
+        node_name: str,
+        prompt_tokens: int,
+        completion_tokens: int,
+        total_tokens: int | None = None,
+        estimated_cost_usd: float | None = None,
+        estimated_raw_prompt_tokens: int | None = None,
+        estimated_tokens_saved: int | None = None,
+        metadata: dict[str, Any] | None = None,
+    ) -> LLMUsageRecord:
+        """Emit a structured ``llm.usage`` event for one model call."""
+
+        total = total_tokens if total_tokens is not None else prompt_tokens + completion_tokens
+        cost = estimated_cost_usd
+        if cost is None:
+            cost = estimate_cost_usd(model, prompt_tokens, completion_tokens)
+
+        record = LLMUsageRecord(
+            task_id=self.task_id,
+            model=model,
+            node_name=node_name,
+            prompt_tokens=prompt_tokens,
+            completion_tokens=completion_tokens,
+            total_tokens=total,
+            estimated_cost_usd=cost,
+            estimated_raw_prompt_tokens=estimated_raw_prompt_tokens,
+            estimated_tokens_saved=estimated_tokens_saved,
+            metadata=metadata or {},
+        )
+        self.emit("llm.usage", record.model_dump(mode="json"))
+        return record
+
     async def wait_for_input(self, prompt: str | None = None) -> str:
         """Block until the user sends freeform text input.
 
diff --git a/src/switchplane/protocol.py b/src/switchplane/protocol.py
index a8c3490..699b079 100644
--- a/src/switchplane/protocol.py
+++ b/src/switchplane/protocol.py
@@ -57,6 +57,7 @@ class AgentEvent(BaseModel):
         "task.interrupted",
         "task.resumed",
         "checkpoint.save",
+        "llm.usage",
         "log",
         "task.command_result",
     ]
diff --git a/src/switchplane/subprocess_manager.py b/src/switchplane/subprocess_manager.py
index e9ae2d5..da3ef9d 100644
--- a/src/switchplane/subprocess_manager.py
+++ b/src/switchplane/subprocess_manager.py
@@ -315,6 +315,8 @@ async def _handle_event(self, event: AgentEvent) -> int:
                 pass
             case "checkpoint.save":
                 pass  # TODO: Forward to checkpoint saver
+            case "llm.usage":
+                pass  # Stored as regular event for task-level cost accounting
             case "task.command_result":
                 pass  # Stored as regular event
             case "log":
diff --git a/src/switchplane/usage.py b/src/switchplane/usage.py
new file mode 100644
index 0000000..f698364
--- /dev/null
+++ b/src/switchplane/usage.py
@@ -0,0 +1,159 @@
+"""LLM usage accounting helpers."""
+
+from __future__ import annotations
+
+import math
+from datetime import UTC, datetime
+from typing import Any, NamedTuple
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class ModelPricing(NamedTuple):
+    """USD prices per one million tokens."""
+
+    input_per_million: float
+    output_per_million: float
+
+
+# Public list-price approximations. Keep this deliberately small; unknown
+# models still produce token records, just without an estimated dollar cost.
+MODEL_PRICING: dict[str, ModelPricing] = {
+    "claude-sonnet-4-20250514": ModelPricing(3.0, 15.0),
+    "claude-sonnet-4-5-20250929": ModelPricing(3.0, 15.0),
+    "claude-sonnet-4-6": ModelPricing(3.0, 15.0),
+    "claude-opus-4-20250514": ModelPricing(15.0, 75.0),
+    "claude-opus-4-6-v1": ModelPricing(15.0, 75.0),
+    "claude-haiku-4-5-20251001": ModelPricing(1.0, 5.0),
+    "gpt-4o": ModelPricing(2.5, 10.0),
+    "gpt-4o-mini": ModelPricing(0.15, 0.60),
+    "gemini-2.0-flash": ModelPricing(0.10, 0.40),
+    "gemini-2.5-flash": ModelPricing(0.30, 2.50),
+    "gemini-2.5-pro": ModelPricing(1.25, 10.0),
+}
+
+
+class LLMUsageRecord(BaseModel):
+    """Structured accounting record for a single LLM call."""
+
+    model_config = ConfigDict(str_strip_whitespace=True)
+
+    task_id: str
+    model: str
+    node_name: str
+    prompt_tokens: int = 0
+    completion_tokens: int = 0
+    total_tokens: int = 0
+    estimated_cost_usd: float | None = None
+    timestamp: datetime = Field(default_factory=lambda: datetime.now(UTC))
+    estimated_raw_prompt_tokens: int | None = None
+    estimated_tokens_saved: int | None = None
+    metadata: dict[str, Any] = Field(default_factory=dict)
+
+
+def estimate_text_tokens(text: str) -> int:
+    """Cheap text token estimate for before/after comparisons.
+
+    Providers expose exact usage after a call, but savings estimates often need
+    a pre-call approximation. Four characters per token is a conservative,
+    model-agnostic rule of thumb for English/code-like text.
+    """
+
+    if not text:
+        return 0
+    return max(1, math.ceil(len(text) / 4))
+
+
+def estimate_cost_usd(model: str, prompt_tokens: int, completion_tokens: int) -> float | None:
+    """Estimate USD cost for a model if pricing is known."""
+
+    pricing = MODEL_PRICING.get(model)
+    if pricing is None:
+        return None
+    cost = (prompt_tokens / 1_000_000 * pricing.input_per_million) + (
+        completion_tokens / 1_000_000 * pricing.output_per_million
+    )
+    return round(cost, 6)
+
+
+def _coerce_int(value: Any) -> int | None:
+    if value is None:
+        return None
+    try:
+        return int(value)
+    except (TypeError, ValueError):
+        return None
+
+
+def extract_token_counts(response: Any) -> tuple[int | None, int | None, int | None]:
+    """Extract provider-reported token counts from common LangChain responses."""
+
+    usage_metadata = getattr(response, "usage_metadata", None)
+    if isinstance(usage_metadata, dict):
+        prompt = _coerce_int(usage_metadata.get("input_tokens") or usage_metadata.get("prompt_tokens"))
+        completion = _coerce_int(
+            usage_metadata.get("output_tokens")
+            or usage_metadata.get("completion_tokens")
+            or usage_metadata.get("generated_tokens")
+        )
+        total = _coerce_int(usage_metadata.get("total_tokens"))
+        if prompt is not None or completion is not None or total is not None:
+            return prompt, completion, total
+
+    response_metadata = getattr(response, "response_metadata", None)
+    if isinstance(response_metadata, dict):
+        token_usage = response_metadata.get("token_usage") or response_metadata.get("usage")
+        if isinstance(token_usage, dict):
+            prompt = _coerce_int(token_usage.get("prompt_tokens") or token_usage.get("input_tokens"))
+            completion = _coerce_int(token_usage.get("completion_tokens") or token_usage.get("output_tokens"))
+            total = _coerce_int(token_usage.get("total_tokens"))
+            if prompt is not None or completion is not None or total is not None:
+                return prompt, completion, total
+
+    return None, None, None
+
+
+def llm_usage_from_response(
+    response: Any,
+    *,
+    task_id: str,
+    model: str,
+    node_name: str,
+    fallback_prompt_text: str = "",
+    fallback_completion_text: str = "",
+    estimated_raw_prompt_tokens: int | None = None,
+    metadata: dict[str, Any] | None = None,
+) -> LLMUsageRecord:
+    """Build an ``LLMUsageRecord`` from a LangChain response."""
+
+    prompt_tokens, completion_tokens, total_tokens = extract_token_counts(response)
+    token_source = "provider"
+
+    if prompt_tokens is None:
+        prompt_tokens = estimate_text_tokens(fallback_prompt_text)
+        token_source = "estimated"
+    if completion_tokens is None:
+        completion_tokens = estimate_text_tokens(fallback_completion_text)
+        token_source = "estimated"
+    if total_tokens is None:
+        total_tokens = prompt_tokens + completion_tokens
+
+    estimated_tokens_saved = None
+    if estimated_raw_prompt_tokens is not None:
+        estimated_tokens_saved = max(0, estimated_raw_prompt_tokens - prompt_tokens)
+
+    meta = dict(metadata or {})
+    meta.setdefault("token_source", token_source)
+
+    return LLMUsageRecord(
+        task_id=task_id,
+        model=model,
+        node_name=node_name,
+        prompt_tokens=prompt_tokens,
+        completion_tokens=completion_tokens,
+        total_tokens=total_tokens,
+        estimated_cost_usd=estimate_cost_usd(model, prompt_tokens, completion_tokens),
+        estimated_raw_prompt_tokens=estimated_raw_prompt_tokens,
+        estimated_tokens_saved=estimated_tokens_saved,
+        metadata=meta,
+    )
diff --git a/tests/test_agent_runtime.py b/tests/test_agent_runtime.py
index a36a651..6d4c779 100644
--- a/tests/test_agent_runtime.py
+++ b/tests/test_agent_runtime.py
@@ -175,6 +175,33 @@ def test_command_result(self, ctx, socketpair):
         assert event.payload["result"]["lat"] == 1.0
 
 
+class TestAgentContextLLMUsage:
+    def test_record_llm_usage(self, ctx, socketpair):
+        cp_sock, _ = socketpair
+        record = ctx.record_llm_usage(
+            model="gpt-4o-mini",
+            node_name="summarize",
+            prompt_tokens=100,
+            completion_tokens=20,
+            estimated_raw_prompt_tokens=500,
+            estimated_tokens_saved=400,
+            metadata={"rows_processed": 10},
+        )
+
+        data = _recv_message(cp_sock)
+        event = AgentEvent.model_validate_json(data)
+        assert event.type == "llm.usage"
+        assert event.payload["task_id"] == "task1"
+        assert event.payload["model"] == "gpt-4o-mini"
+        assert event.payload["node_name"] == "summarize"
+        assert event.payload["prompt_tokens"] == 100
+        assert event.payload["completion_tokens"] == 20
+        assert event.payload["total_tokens"] == 120
+        assert event.payload["estimated_tokens_saved"] == 400
+        assert event.payload["metadata"]["rows_processed"] == 10
+        assert record.total_tokens == 120
+
+
 class TestAgentContextProperties:
     def test_config(self, ctx):
         assert ctx.config == {"llm": {"model": "test"}}
diff --git a/tests/test_protocol.py b/tests/test_protocol.py
index 8c4046e..8afc9d3 100644
--- a/tests/test_protocol.py
+++ b/tests/test_protocol.py
@@ -83,6 +83,7 @@ def test_valid_types(self):
             "task.failed",
             "task.cancelled",
             "checkpoint.save",
+            "llm.usage",
             "log",
             "task.command_result",
         ]
diff --git a/tests/test_usage.py b/tests/test_usage.py
new file mode 100644
index 0000000..454000f
--- /dev/null
+++ b/tests/test_usage.py
@@ -0,0 +1,66 @@
+from types import SimpleNamespace
+
+from switchplane.usage import estimate_cost_usd, estimate_text_tokens, extract_token_counts, llm_usage_from_response
+
+
+def test_estimate_text_tokens_uses_four_chars_per_token():
+    assert estimate_text_tokens("") == 0
+    assert estimate_text_tokens("abcd") == 1
+    assert estimate_text_tokens("abcde") == 2
+
+
+def test_extract_token_counts_from_usage_metadata():
+    response = SimpleNamespace(usage_metadata={"input_tokens": 10, "output_tokens": 5, "total_tokens": 15})
+
+    assert extract_token_counts(response) == (10, 5, 15)
+
+
+def test_extract_token_counts_from_response_metadata():
+    response = SimpleNamespace(response_metadata={"token_usage": {"prompt_tokens": 20, "completion_tokens": 7}})
+
+    assert extract_token_counts(response) == (20, 7, None)
+
+
+def test_estimate_cost_for_known_model():
+    assert estimate_cost_usd("gpt-4o-mini", 1_000_000, 1_000_000) == 0.75
+
+
+def test_usage_from_response_uses_provider_counts():
+    response = SimpleNamespace(
+        content="ok",
+        usage_metadata={"input_tokens": 100, "output_tokens": 25, "total_tokens": 125},
+    )
+
+    usage = llm_usage_from_response(
+        response,
+        task_id="task1",
+        model="claude-sonnet-4-20250514",
+        node_name="summarize",
+        estimated_raw_prompt_tokens=1_000,
+    )
+
+    assert usage.task_id == "task1"
+    assert usage.prompt_tokens == 100
+    assert usage.completion_tokens == 25
+    assert usage.total_tokens == 125
+    assert usage.estimated_tokens_saved == 900
+    assert usage.metadata["token_source"] == "provider"
+
+
+def test_usage_from_response_falls_back_to_estimates():
+    response = SimpleNamespace(content="hello world")
+
+    usage = llm_usage_from_response(
+        response,
+        task_id="task1",
+        model="unknown-model",
+        node_name="summarize",
+        fallback_prompt_text="abcd",
+        fallback_completion_text=response.content,
+    )
+
+    assert usage.prompt_tokens == 1
+    assert usage.completion_tokens == 3
+    assert usage.total_tokens == 4
+    assert usage.estimated_cost_usd is None
+    assert usage.metadata["token_source"] == "estimated"