Add /v1/messages/count_tokens endpoint documentation (#17772)

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

docs/my-website/docs/anthropic_count_tokens.md

@@ -0,0 +1,231 @@
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
+# /v1/messages/count_tokens
+
+## Overview
+
+Anthropic-compatible token counting endpoint. Count tokens for messages before sending them to the model.
+
+| Feature | Supported | Notes |
+|---------|-----------|-------|
+| Cost Tracking | ❌ | Token counting only, no cost incurred |
+| Logging | ✅ | Works across all integrations |
+| End-user Tracking | ✅ | |
+| Supported Providers | Anthropic, Vertex AI (Claude), Bedrock (Claude), Gemini, Vertex AI | Auto-routes to provider-specific token counting APIs |
+
+## Quick Start
+
+### 1. Start LiteLLM Proxy
+
+```bash
+litellm --config /path/to/config.yaml
+
+# RUNNING on http://0.0.0.0:4000
+```
+
+### 2. Count Tokens
+
+<Tabs>
+<TabItem value="curl" label="curl">
+
+```bash
+curl -X POST "http://localhost:4000/v1/messages/count_tokens" \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer sk-1234" \
+  -d '{
+    "model": "claude-3-5-sonnet-20241022",
+    "messages": [
+      {"role": "user", "content": "Hello, how are you?"}
+    ]
+  }'
+```
+
+</TabItem>
+<TabItem value="python" label="Python (httpx)">
+
+```python
+import httpx
+
+response = httpx.post(
+    "http://localhost:4000/v1/messages/count_tokens",
+    headers={
+        "Content-Type": "application/json",
+        "Authorization": "Bearer sk-1234"
+    },
+    json={
+        "model": "claude-3-5-sonnet-20241022",
+        "messages": [
+            {"role": "user", "content": "Hello, how are you?"}
+        ]
+    }
+)
+
+print(response.json())
+# {"input_tokens": 14}
+```
+
+</TabItem>
+</Tabs>
+
+**Expected Response:**
+
+```json
+{
+  "input_tokens": 14
+}
+```
+
+## LiteLLM Proxy Configuration
+
+Add models to your `config.yaml`:
+
+```yaml
+model_list:
+  - model_name: claude-3-5-sonnet
+    litellm_params:
+      model: anthropic/claude-3-5-sonnet-20241022
+      api_key: os.environ/ANTHROPIC_API_KEY
+
+  - model_name: claude-vertex
+    litellm_params:
+      model: vertex_ai/claude-3-5-sonnet-v2@20241022
+      vertex_project: my-project
+      vertex_location: us-east5
+
+  - model_name: claude-bedrock
+    litellm_params:
+      model: bedrock/anthropic.claude-3-5-sonnet-20241022-v2:0
+      aws_region_name: us-west-2
+```
+
+## Request Parameters
+
+| Parameter | Type | Required | Description |
+|-----------|------|----------|-------------|
+| `model` | string | ✅ | The model to use for token counting |
+| `messages` | array | ✅ | Array of messages in Anthropic format |
+
+### Messages Format
+
+```json
+{
+  "messages": [
+    {"role": "user", "content": "Hello!"},
+    {"role": "assistant", "content": "Hi there!"},
+    {"role": "user", "content": "How are you?"}
+  ]
+}
+```
+
+## Response Format
+
+```json
+{
+  "input_tokens": <number>
+}
+```
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `input_tokens` | integer | Number of tokens in the input messages |
+
+## Supported Providers
+
+The `/v1/messages/count_tokens` endpoint automatically routes to the appropriate provider-specific token counting API:
+
+| Provider | Token Counting Method |
+|----------|----------------------|
+| Anthropic | [Anthropic Token Counting API](https://docs.anthropic.com/en/docs/build-with-claude/token-counting) |
+| Vertex AI (Claude) | Vertex AI Partner Models Token Counter |
+| Bedrock (Claude) | AWS Bedrock CountTokens API |
+| Gemini | Google AI Studio countTokens API |
+| Vertex AI (Gemini) | Vertex AI countTokens API |
+
+## Examples
+
+### Count Tokens with System Message
+
+```bash
+curl -X POST "http://localhost:4000/v1/messages/count_tokens" \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer sk-1234" \
+  -d '{
+    "model": "claude-3-5-sonnet-20241022",
+    "messages": [
+      {"role": "user", "content": "You are a helpful assistant. Please help me write a haiku about programming."}
+    ]
+  }'
+```
+
+### Count Tokens for Multi-turn Conversation
+
+```bash
+curl -X POST "http://localhost:4000/v1/messages/count_tokens" \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer sk-1234" \
+  -d '{
+    "model": "claude-3-5-sonnet-20241022",
+    "messages": [
+      {"role": "user", "content": "What is the capital of France?"},
+      {"role": "assistant", "content": "The capital of France is Paris."},
+      {"role": "user", "content": "What is its population?"}
+    ]
+  }'
+```
+
+### Using with Vertex AI Claude
+
+```bash
+curl -X POST "http://localhost:4000/v1/messages/count_tokens" \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer sk-1234" \
+  -d '{
+    "model": "claude-vertex",
+    "messages": [
+      {"role": "user", "content": "Hello, world!"}
+    ]
+  }'
+```
+
+### Using with Bedrock Claude
+
+```bash
+curl -X POST "http://localhost:4000/v1/messages/count_tokens" \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer sk-1234" \
+  -d '{
+    "model": "claude-bedrock",
+    "messages": [
+      {"role": "user", "content": "Hello, world!"}
+    ]
+  }'
+```
+
+## Comparison with Anthropic Passthrough
+
+LiteLLM provides two ways to count tokens:
+
+| Endpoint | Description | Use Case |
+|----------|-------------|----------|
+| `/v1/messages/count_tokens` | LiteLLM's Anthropic-compatible endpoint | Works with all supported providers (Anthropic, Vertex AI, Bedrock, etc.) |
+| `/anthropic/v1/messages/count_tokens` | [Pass-through to Anthropic API](./pass_through/anthropic_completion.md#example-2-token-counting-api) | Direct Anthropic API access with native headers |
+
+### Pass-through Example
+
+For direct Anthropic API access with full native headers:
+
+```bash
+curl --request POST \
+    --url http://0.0.0.0:4000/anthropic/v1/messages/count_tokens \
+    --header "x-api-key: $LITELLM_API_KEY" \
+    --header "anthropic-version: 2023-06-01" \
+    --header "anthropic-beta: token-counting-2024-11-01" \
+    --header "content-type: application/json" \
+    --data '{
+        "model": "claude-3-5-sonnet-20241022",
+        "messages": [
+            {"role": "user", "content": "Hello, world"}
+        ]
+    }'
+```

docs/my-website/sidebars.js

@@ -493,6 +493,7 @@ const sidebars = {
           ]
         },
         "anthropic_unified",
+        "anthropic_count_tokens",
         "moderation",
         "ocr",
         {