diff --git a/docs/observability/ternary.md b/docs/observability/ternary.md
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+# Ternary
+
+LiteLLM can export proxy spend data to [Ternary](https://ternary.app) as [FOCUS 1.2](https://focus.finops.org/) formatted cost reports. This lets you allocate and analyse LLM spend alongside your cloud costs in Ternary's FinOps platform — for example, splitting a shared AI invoice across teams, projects, and API keys.
+
+## Overview
+
+| Property | Details |
+|----------|---------|
+| Destination | Export LiteLLM usage data to a Ternary AI Gateway cost connection |
+| Data format | FOCUS CSV (automatically transformed from LiteLLM spend data) |
+| Supported operations | Automatic scheduled export (daily; interval for setup validation) |
+| Authentication | Ternary API key + connection ID (per-connection bearer token) |
+| Privacy | Cost and usage metadata only — no prompt or completion content leaves the gateway |
+
+## Prerequisites
+
+You need three values from Ternary:
+
+1. **Connection ID** (`TERNARY_CONNECTION_ID`) — identifies the cost connection the data lands in; it appears in the export URL path.
+2. **API Key** (`TERNARY_API_KEY`) — a per-connection bearer token that authenticates the push.
+3. **API host** (`TERNARY_BASE_URL`) — your Ternary API host, which differs by region (US vs EU).
+
+The Connection ID and API Key are minted when you add an **AI Gateway** integration in Ternary (**Settings → Integrations → Add integration → AI Gateway**). The API host is the base URL of the Ternary instance you sign in to — the US and EU regions have different hosts.
+
+## Setup
+
+### Environment variables
+
+| Variable | Required | Description |
+|----------|----------|-------------|
+| `TERNARY_API_KEY` | Yes | Per-connection bearer token from the Ternary AI Gateway integration |
+| `TERNARY_CONNECTION_ID` | Yes | Cost connection identifier (used in the export URL path) |
+| `TERNARY_BASE_URL` | Yes | Your Ternary API host (region-specific, US vs EU). No default is assumed. |
+| `TERNARY_EXPORT_FREQUENCY` | No | `daily` (default), or `interval` for short setup-validation loops. LiteLLM spend is a daily aggregate, so there is no sub-daily cadence. |
+| `TERNARY_EXPORT_INTERVAL_SECONDS` | No | Seconds between exports when frequency is `interval` (intended for short setup-validation / test loops) |
+
+### Proxy config
+
+```yaml
+model_list:
+  - model_name: gpt-4o
+    litellm_params:
+      model: openai/gpt-4o
+      api_key: sk-your-key
+
+litellm_settings:
+  callbacks: ["ternary"]
+```
+
+```bash
+export TERNARY_API_KEY="<your-connection-api-key>"
+export TERNARY_CONNECTION_ID="<your-connection-id>"
+export TERNARY_BASE_URL="<your-ternary-api-host>"   # region-specific (US vs EU)
+litellm --config /path/to/config.yaml
+```
+
+The proxy registers a background job that exports FOCUS-formatted spend data on the configured schedule.
+
+## How it works
+
+On each scheduled run LiteLLM transforms recent spend into a FOCUS 1.2 CSV and POSTs it to your Ternary cost connection:
+
+- **Endpoint:** `POST {TERNARY_BASE_URL}/external-cost-sources/v1/{TERNARY_CONNECTION_ID}/focus`
+- **Auth:** `Authorization: Bearer {TERNARY_API_KEY}`
+- **Body:** `multipart/form-data`, field `csv`
+
+Ternary derives the affected date range from the data itself (`ChargePeriodStart`) and replaces those days on each push, so a re-sent day updates in place rather than double-counting. Large exports are chunked (see [Upload limits](#upload-limits)); every chunk of one export shares a stable upload id, so Ternary stages the parts and commits the whole export atomically once all parts have arrived — safe for backfills and retries.
+
+## Privacy
+
+Only cost and usage **metadata** is exported — spend, token counts, model, provider, and team/key identifiers. Prompt and completion **content never leaves the gateway**.
+
+## Cost provenance (estimate vs. billed)
+
+Gateway-reported spend is a rate-card **estimate**, not a billed invoice. Ternary tags every row landed through this connection with its provenance (a cost source of `"LiteLLM estimate"`), derived server-side from the connection — so estimated gateway spend is never mistaken for, or reallocated as, billed cloud cost. Keep the gateway's spend scoped as the estimate it is to avoid double-counting against a separate provider invoice.
+
+## FOCUS field mapping
+
+LiteLLM spend data is transformed into the FOCUS 1.2 schema (the same shared transformer used by the other FOCUS destinations):
+
+| LiteLLM field | FOCUS column | Description |
+|---------------|--------------|-------------|
+| `spend` | BilledCost, EffectiveCost, ListCost, ContractedCost | Cost of the usage (gateway estimate) |
+| `model` | ChargeDescription, ResourceId | Model identifier |
+| `model_group` | ServiceName | Model group / deployment |
+| `custom_llm_provider` | ProviderName, PublisherName | Provider (openai, anthropic, …) |
+| `api_key` | BillingAccountId | Hashed API key |
+| `api_key_alias` | BillingAccountName | Human-readable key alias |
+| `team_id` | SubAccountId | Team identifier |
+| `team_alias` | SubAccountName | Team name |
+| `organization_id` / `organization_alias` | Tags | Organization identifier / display name |
+
+### Token breakdown
+
+Per-request token counts — `prompt_tokens`, `completion_tokens`, `cache_read_input_tokens`, `cache_creation_input_tokens` — which the shared FOCUS transformer does not surface as top-level columns, are carried in the standard FOCUS **`Tags`** column as JSON. Ternary reads them from `Tags` on ingest to enable token-weighted cost allocation. Other metadata (`user_id`, `user_email`, `model`, …) also rides in `Tags`.
+
+## Upload limits
+
+Ternary's receiver accepts large exports; LiteLLM chunks automatically:
+
+- **10,000 rows** per upload; larger exports are split into parts.
+- **2 MB** per upload; oversized batches are split further by size.
+- Each part of one export shares an upload id (`X-Ternary-Upload-Id`) plus its index and total, so Ternary commits the export exactly once, after all parts arrive — no partial or double-counted data.
+
+## Related Links
+
+- [Ternary](https://ternary.app)
+- [FOCUS Specification](https://focus.finops.org/)
+- [Focus Export (S3 / GCS / Parquet)](./focus.md)
diff --git a/sidebars.js b/sidebars.js
index 4bbeb3866..9ea33e40c 100644
--- a/sidebars.js
+++ b/sidebars.js
@@ -97,6 +97,7 @@ const sidebars = {
             "observability/mavvrik",
             "observability/openmeter",
             "observability/ramp_integration",
+            "observability/ternary",
             "observability/vantage",
           ],
         },