diff --git a/modules/api/anthropic.py b/modules/api/anthropic.py
new file mode 100644
index 00000000..5fbf5caf
--- /dev/null
+++ b/modules/api/anthropic.py
@@ -0,0 +1,468 @@
+import json
+import time
+
+from modules import shared
+
+
+def convert_request(body: dict) -> dict:
+    """Transform Anthropic Messages API body into the dict that chat_completions_common expects."""
+    messages = []
+
+    # System message
+    system = body.get('system')
+    if system:
+        if isinstance(system, list):
+            # List of content blocks like [{"type":"text","text":"..."}]
+            text_parts = [block.get('text', '') for block in system if isinstance(block, dict) and block.get('type') == 'text']
+            system_text = '\n'.join(text_parts)
+        else:
+            system_text = str(system)
+        if system_text:
+            messages.append({"role": "system", "content": system_text})
+
+    # Convert messages
+    for msg in body.get('messages', []):
+        role = msg.get('role')
+        content = msg.get('content')
+
+        if isinstance(content, str):
+            messages.append({"role": role, "content": content})
+            continue
+
+        if not isinstance(content, list):
+            messages.append({"role": role, "content": str(content) if content else ""})
+            continue
+
+        if role == 'assistant':
+            # Split into text content, tool_calls, and skip thinking blocks
+            text_parts = []
+            tool_calls = []
+            for block in content:
+                btype = block.get('type')
+                if btype == 'text':
+                    text_parts.append(block.get('text', ''))
+                elif btype == 'tool_use':
+                    tool_calls.append({
+                        "id": block.get('id', ''),
+                        "type": "function",
+                        "function": {
+                            "name": block.get('name', ''),
+                            "arguments": json.dumps(block.get('input', {}))
+                        }
+                    })
+                elif btype == 'thinking':
+                    pass  # Strip thinking blocks
+
+            assistant_msg = {"role": "assistant", "content": '\n'.join(text_parts) if text_parts else ""}
+            if tool_calls:
+                assistant_msg["tool_calls"] = tool_calls
+            messages.append(assistant_msg)
+
+        elif role == 'user':
+            # Handle tool_result blocks and regular content
+            regular_parts = []
+            for block in content:
+                btype = block.get('type')
+                if btype == 'tool_result':
+                    # Emit any accumulated regular content first
+                    if regular_parts:
+                        if len(regular_parts) == 1 and regular_parts[0].get('type') == 'text':
+                            messages.append({"role": "user", "content": regular_parts[0]['text']})
+                        else:
+                            messages.append({"role": "user", "content": regular_parts})
+                        regular_parts = []
+                    # Convert tool_result to OpenAI tool message
+                    tool_content = block.get('content', '')
+                    if isinstance(tool_content, list):
+                        tool_content = '\n'.join(
+                            b.get('text', '') for b in tool_content
+                            if isinstance(b, dict) and b.get('type') == 'text'
+                        )
+                    messages.append({
+                        "role": "tool",
+                        "tool_call_id": block.get('tool_use_id', ''),
+                        "content": str(tool_content)
+                    })
+                elif btype == 'text':
+                    regular_parts.append({"type": "text", "text": block.get('text', '')})
+                elif btype == 'image':
+                    source = block.get('source', {})
+                    if source.get('type') == 'base64':
+                        media_type = source.get('media_type', 'image/png')
+                        data = source.get('data', '')
+                        regular_parts.append({
+                            "type": "image_url",
+                            "image_url": {"url": f"data:{media_type};base64,{data}"}
+                        })
+                elif btype == 'thinking':
+                    pass  # Strip thinking blocks
+
+            if regular_parts:
+                if len(regular_parts) == 1 and regular_parts[0].get('type') == 'text':
+                    messages.append({"role": "user", "content": regular_parts[0]['text']})
+                else:
+                    messages.append({"role": "user", "content": regular_parts})
+        else:
+            messages.append({"role": role, "content": str(content)})
+
+    # Start with all fields from the original body (includes GenerationOptions defaults)
+    result = dict(body)
+
+    # Remove Anthropic-specific fields that don't map directly
+    for key in ('system', 'stop_sequences', 'tools', 'tool_choice', 'thinking', 'metadata'):
+        result.pop(key, None)
+
+    # Set converted fields
+    result['messages'] = messages
+    result['max_tokens'] = body.get('max_tokens', 4096)
+    result['stream'] = body.get('stream', False)
+    result['mode'] = 'instruct'
+
+    # Ensure ChatCompletionRequestParams defaults are present
+    result.setdefault('continue_', False)
+    result.setdefault('instruction_template', None)
+    result.setdefault('instruction_template_str', None)
+    result.setdefault('character', None)
+    result.setdefault('bot_name', None)
+    result.setdefault('context', None)
+    result.setdefault('greeting', None)
+    result.setdefault('user_name', None)
+    result.setdefault('user_bio', None)
+    result.setdefault('chat_template_str', None)
+    result.setdefault('chat_instruct_command', 'Continue the chat dialogue below. Write a single reply for the character "<|character|>".\n\n<|prompt|>')
+    result.setdefault('frequency_penalty', None)
+    result.setdefault('presence_penalty', None)
+    result.setdefault('logit_bias', None)
+    result.setdefault('logprobs', None)
+    result.setdefault('top_logprobs', None)
+    result.setdefault('n', 1)
+    result.setdefault('model', None)
+    result.setdefault('functions', None)
+    result.setdefault('function_call', None)
+    result.setdefault('stream_options', None)
+    result.setdefault('user', None)
+    result.setdefault('stop', None)
+    result.setdefault('tool_choice', None)
+
+    # Always request usage in streaming so the usage-only chunk triggers
+    # the deferred message_delta/message_stop with accurate output_tokens
+    if body.get('stream', False):
+        result['stream_options'] = {'include_usage': True}
+
+    # Map stop_sequences -> stop
+    if body.get('stop_sequences'):
+        result['stop'] = body['stop_sequences']
+
+    # Tools
+    if body.get('tools'):
+        result['tools'] = [
+            {
+                "type": "function",
+                "function": {
+                    "name": t.get('name', ''),
+                    "description": t.get('description', ''),
+                    "parameters": t.get('input_schema', {"type": "object", "properties": {}})
+                }
+            }
+            for t in body['tools']
+        ]
+
+    # Tool choice
+    tc = body.get('tool_choice')
+    if tc and isinstance(tc, dict):
+        tc_type = tc.get('type')
+        if tc_type == 'auto':
+            result['tool_choice'] = 'auto'
+        elif tc_type == 'any':
+            result['tool_choice'] = 'required'
+        elif tc_type == 'tool':
+            result['tool_choice'] = {"type": "function", "function": {"name": tc.get('name', '')}}
+        elif tc_type == 'none':
+            result['tool_choice'] = 'none'
+    else:
+        result.setdefault('tool_choice', None)
+
+    # Thinking
+    thinking = body.get('thinking')
+    if thinking and isinstance(thinking, dict) and thinking.get('type') in ('enabled', 'adaptive'):
+        result['enable_thinking'] = True
+
+    return result
+
+
+_FINISH_REASON_MAP = {
+    "stop": "end_turn",
+    "length": "max_tokens",
+    "tool_calls": "tool_use",
+}
+
+
+def build_response(openai_resp: dict, model: str) -> dict:
+    """Transform OpenAI chat completion response dict into Anthropic Messages format."""
+    resp_id = openai_resp.get('id', 'msg_unknown')
+    if resp_id.startswith('chatcmpl-'):
+        resp_id = 'msg_' + resp_id[9:]
+
+    choice = openai_resp.get('choices', [{}])[0]
+    message = choice.get('message', {})
+
+    content = []
+
+    # Reasoning/thinking content
+    reasoning = message.get('reasoning_content')
+    if reasoning:
+        content.append({"type": "thinking", "thinking": reasoning, "signature": ""})
+
+    # Text content
+    text = message.get('content')
+    if text:
+        content.append({"type": "text", "text": text})
+
+    # Tool calls
+    tool_calls = message.get('tool_calls')
+    if tool_calls:
+        for tc in tool_calls:
+            func = tc.get('function', {})
+            try:
+                input_data = json.loads(func.get('arguments', '{}'))
+            except (json.JSONDecodeError, TypeError):
+                input_data = {}
+            content.append({
+                "type": "tool_use",
+                "id": tc.get('id', ''),
+                "name": func.get('name', ''),
+                "input": input_data
+            })
+
+    finish_reason = choice.get('finish_reason', 'stop')
+    stop_reason = _FINISH_REASON_MAP.get(finish_reason, 'end_turn')
+
+    usage = openai_resp.get('usage', {})
+
+    return {
+        "id": resp_id,
+        "type": "message",
+        "role": "assistant",
+        "content": content,
+        "model": model,
+        "stop_reason": stop_reason,
+        "stop_sequence": None,
+        "usage": {
+            "input_tokens": usage.get('prompt_tokens', 0),
+            "output_tokens": usage.get('completion_tokens', 0),
+        }
+    }
+
+
+class StreamConverter:
+    """Stateful converter: processes one OpenAI chunk at a time, yields Anthropic SSE events.
+
+    When include_usage is enabled in the OpenAI request, the final chunk with
+    finish_reason has usage=None, followed by a separate usage-only chunk
+    (choices=[], usage={...}).  We defer emitting message_delta and message_stop
+    until we receive that usage chunk so output_tokens is accurate.
+    """
+
+    def __init__(self, model: str):
+        self.model = model
+        self.msg_id = "msg_%d" % int(time.time() * 1000000000)
+        self.block_index = 0
+        self.in_thinking = False
+        self.in_text = False
+        self.input_tokens = 0
+        self.output_tokens = 0
+        self.tool_calls_accum = {}
+        self.stop_reason = "end_turn"
+        self._pending_finish = False  # True after we've seen finish_reason
+
+    def process_chunk(self, chunk: dict) -> list[dict]:
+        """Process a single OpenAI streaming chunk; return list of Anthropic SSE event dicts."""
+        events = []
+        choices = chunk.get('choices', [])
+        usage = chunk.get('usage')
+
+        if usage:
+            self.input_tokens = usage.get('prompt_tokens', self.input_tokens)
+            self.output_tokens = usage.get('completion_tokens', self.output_tokens)
+
+        # Usage-only chunk (choices=[]) arrives after the finish chunk
+        if not choices:
+            if self._pending_finish:
+                events.extend(self.finish())
+            return events
+
+        choice = choices[0]
+        delta = choice.get('delta', {})
+        finish_reason = choice.get('finish_reason')
+
+        # First chunk with role
+        if 'role' in delta:
+            events.append({
+                "event": "message_start",
+                "data": json.dumps({
+                    "type": "message_start",
+                    "message": {
+                        "id": self.msg_id,
+                        "type": "message",
+                        "role": "assistant",
+                        "content": [],
+                        "model": self.model,
+                        "stop_reason": None,
+                        "stop_sequence": None,
+                        "usage": {"input_tokens": self.input_tokens, "output_tokens": 0}
+                    }
+                })
+            })
+            events.append({"event": "ping", "data": json.dumps({"type": "ping"})})
+            return events
+
+        # Reasoning content
+        reasoning_content = delta.get('reasoning_content')
+        if reasoning_content:
+            if not self.in_thinking:
+                self.in_thinking = True
+                events.append({
+                    "event": "content_block_start",
+                    "data": json.dumps({
+                        "type": "content_block_start",
+                        "index": self.block_index,
+                        "content_block": {"type": "thinking", "thinking": ""}
+                    })
+                })
+            events.append({
+                "event": "content_block_delta",
+                "data": json.dumps({
+                    "type": "content_block_delta",
+                    "index": self.block_index,
+                    "delta": {"type": "thinking_delta", "thinking": reasoning_content}
+                })
+            })
+            return events
+
+        # Text content
+        text_content = delta.get('content')
+        if text_content:
+            if self.in_thinking:
+                events.append({
+                    "event": "content_block_stop",
+                    "data": json.dumps({"type": "content_block_stop", "index": self.block_index})
+                })
+                self.in_thinking = False
+                self.block_index += 1
+
+            if not self.in_text:
+                self.in_text = True
+                events.append({
+                    "event": "content_block_start",
+                    "data": json.dumps({
+                        "type": "content_block_start",
+                        "index": self.block_index,
+                        "content_block": {"type": "text", "text": ""}
+                    })
+                })
+            events.append({
+                "event": "content_block_delta",
+                "data": json.dumps({
+                    "type": "content_block_delta",
+                    "index": self.block_index,
+                    "delta": {"type": "text_delta", "text": text_content}
+                })
+            })
+            return events
+
+        # Tool calls in delta
+        chunk_tool_calls = delta.get('tool_calls')
+        if chunk_tool_calls:
+            for tc in chunk_tool_calls:
+                tc_id = tc.get('id', '')
+                tc_idx = tc.get('index', 0)
+                func = tc.get('function', {})
+                if tc_id:
+                    self.tool_calls_accum[tc_idx] = {
+                        "id": tc_id,
+                        "name": func.get('name', ''),
+                        "arguments": func.get('arguments', '')
+                    }
+                elif tc_idx in self.tool_calls_accum:
+                    self.tool_calls_accum[tc_idx]["arguments"] += func.get('arguments', '')
+
+        # Final chunk — close open content blocks, defer message_delta/stop for usage
+        if finish_reason is not None:
+            self.stop_reason = _FINISH_REASON_MAP.get(finish_reason, 'end_turn')
+
+            if self.in_thinking:
+                events.append({
+                    "event": "content_block_stop",
+                    "data": json.dumps({"type": "content_block_stop", "index": self.block_index})
+                })
+                self.in_thinking = False
+                self.block_index += 1
+
+            if self.in_text:
+                events.append({
+                    "event": "content_block_stop",
+                    "data": json.dumps({"type": "content_block_stop", "index": self.block_index})
+                })
+                self.in_text = False
+                self.block_index += 1
+
+            for tc_idx in sorted(self.tool_calls_accum.keys()):
+                tc = self.tool_calls_accum[tc_idx]
+                arguments_str = tc["arguments"] or "{}"
+
+                events.append({
+                    "event": "content_block_start",
+                    "data": json.dumps({
+                        "type": "content_block_start",
+                        "index": self.block_index,
+                        "content_block": {
+                            "type": "tool_use",
+                            "id": tc["id"],
+                            "name": tc["name"],
+                            "input": {}
+                        }
+                    })
+                })
+                # Emit the full input as a single input_json_delta so SDK
+                # clients that reconstruct from deltas get the correct data
+                events.append({
+                    "event": "content_block_delta",
+                    "data": json.dumps({
+                        "type": "content_block_delta",
+                        "index": self.block_index,
+                        "delta": {
+                            "type": "input_json_delta",
+                            "partial_json": arguments_str
+                        }
+                    })
+                })
+                events.append({
+                    "event": "content_block_stop",
+                    "data": json.dumps({"type": "content_block_stop", "index": self.block_index})
+                })
+                self.block_index += 1
+
+            # Defer message_delta/stop — usage chunk may follow
+            self._pending_finish = True
+
+        return events
+
+    def finish(self) -> list[dict]:
+        """Emit deferred message_delta and message_stop. Safe to call multiple times."""
+        if not self._pending_finish:
+            return []
+        self._pending_finish = False
+        return [
+            {
+                "event": "message_delta",
+                "data": json.dumps({
+                    "type": "message_delta",
+                    "delta": {"stop_reason": self.stop_reason, "stop_sequence": None},
+                    "usage": {"input_tokens": self.input_tokens, "output_tokens": self.output_tokens}
+                })
+            },
+            {
+                "event": "message_stop",
+                "data": json.dumps({"type": "message_stop"})
+            }
+        ]
diff --git a/modules/api/script.py b/modules/api/script.py
index 356919e9..a94247fa 100644
--- a/modules/api/script.py
+++ b/modules/api/script.py
@@ -10,6 +10,7 @@ from threading import Thread
 
 import uvicorn
 from fastapi import Depends, FastAPI, Header, HTTPException
+from fastapi.exceptions import RequestValidationError
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.requests import Request
 from fastapi.responses import JSONResponse
@@ -19,6 +20,7 @@ from starlette.concurrency import iterate_in_threadpool
 import modules.api.completions as OAIcompletions
 import modules.api.logits as OAIlogits
 import modules.api.models as OAImodels
+import modules.api.anthropic as Anthropic
 from .tokens import token_count, token_decode, token_encode
 from .errors import OpenAIError
 from .utils import _start_cloudflared
@@ -28,6 +30,7 @@ from modules.models import unload_model
 from modules.text_generation import stop_everything_event  # used by /v1/internal/stop-generation
 
 from .typing import (
+    AnthropicRequest,
     ChatCompletionRequest,
     ChatCompletionResponse,
     ChatPromptResponse,
@@ -74,9 +77,23 @@ def verify_admin_key(authorization: str = Header(None)) -> None:
         raise HTTPException(status_code=401, detail="Unauthorized")
 
 
+def verify_anthropic_key(x_api_key: str = Header(None, alias="x-api-key")) -> None:
+    expected_api_key = shared.args.api_key
+    if expected_api_key and (x_api_key is None or x_api_key != expected_api_key):
+        raise HTTPException(status_code=401, detail="Unauthorized")
+
+
+class AnthropicError(Exception):
+    def __init__(self, message: str, error_type: str = "invalid_request_error", status_code: int = 400):
+        self.message = message
+        self.error_type = error_type
+        self.status_code = status_code
+
+
 app = FastAPI()
 check_key = [Depends(verify_api_key)]
 check_admin_key = [Depends(verify_admin_key)]
+check_anthropic_key = [Depends(verify_anthropic_key)]
 
 # Configure CORS settings to allow all origins, methods, and headers
 app.add_middleware(
@@ -102,6 +119,28 @@ async def openai_error_handler(request: Request, exc: OpenAIError):
     )
 
 
+@app.exception_handler(AnthropicError)
+async def anthropic_error_handler(request: Request, exc: AnthropicError):
+    return JSONResponse(
+        status_code=exc.status_code,
+        content={"type": "error", "error": {"type": exc.error_type, "message": exc.message}}
+    )
+
+
+@app.exception_handler(RequestValidationError)
+async def validation_error_handler(request: Request, exc: RequestValidationError):
+    if request.url.path.startswith("/v1/messages"):
+        messages = "; ".join(
+            f"{'.'.join(str(l) for l in e['loc'])}: {e['msg']}" for e in exc.errors()
+        )
+        return JSONResponse(
+            status_code=400,
+            content={"type": "error", "error": {"type": "invalid_request_error", "message": messages}}
+        )
+
+    return JSONResponse(status_code=422, content={"detail": exc.errors()})
+
+
 @app.middleware("http")
 async def validate_host_header(request: Request, call_next):
     # Be strict about only approving access to localhost by default
@@ -211,6 +250,76 @@ async def openai_chat_completions(request: Request, request_data: ChatCompletion
         return JSONResponse(response)
 
 
+@app.post('/v1/messages', dependencies=check_anthropic_key)
+async def anthropic_messages(request: Request, request_data: AnthropicRequest):
+    body = to_dict(request_data)
+    model = body.get('model') or shared.model_name or 'unknown'
+
+    try:
+        converted = Anthropic.convert_request(body)
+    except Exception as e:
+        raise AnthropicError(message=str(e))
+
+    try:
+        return await _anthropic_generate(request, request_data, converted, model)
+    except OpenAIError as e:
+        error_type = "invalid_request_error" if e.code < 500 else "api_error"
+        if e.code == 503:
+            error_type = "overloaded_error"
+        raise AnthropicError(message=e.message, error_type=error_type, status_code=e.code)
+    except Exception as e:
+        raise AnthropicError(message=str(e) or "Internal server error", error_type="api_error", status_code=500)
+
+
+async def _anthropic_generate(request, request_data, converted, model):
+    if request_data.stream:
+        stop_event = threading.Event()
+
+        async def generator():
+            converter = Anthropic.StreamConverter(model)
+            response = OAIcompletions.stream_chat_completions(converted, is_legacy=False, stop_event=stop_event)
+            try:
+                async for resp in iterate_in_threadpool(response):
+                    disconnected = await request.is_disconnected()
+                    if disconnected:
+                        break
+
+                    for event in converter.process_chunk(resp):
+                        yield event
+
+                for event in converter.finish():
+                    yield event
+            except OpenAIError as e:
+                error_type = "invalid_request_error" if e.code < 500 else "api_error"
+                if e.code == 503:
+                    error_type = "overloaded_error"
+                yield {
+                    "event": "error",
+                    "data": json.dumps({"type": "error", "error": {"type": error_type, "message": e.message}})
+                }
+            finally:
+                stop_event.set()
+                response.close()
+
+        return EventSourceResponse(generator(), sep="\n")
+
+    else:
+        stop_event = threading.Event()
+        monitor = asyncio.create_task(_wait_for_disconnect(request, stop_event))
+        try:
+            openai_resp = await asyncio.to_thread(
+                OAIcompletions.chat_completions,
+                converted,
+                is_legacy=False,
+                stop_event=stop_event
+            )
+        finally:
+            stop_event.set()
+            monitor.cancel()
+
+        return JSONResponse(Anthropic.build_response(openai_resp, model))
+
+
 @app.get("/v1/models", dependencies=check_key)
 @app.get("/v1/models/{model}", dependencies=check_key)
 async def handle_models(request: Request):
@@ -469,15 +578,15 @@ def run_server():
             port,
             shared.args.public_api_id,
             max_attempts=3,
-            on_start=lambda url: logger.info(f'OpenAI-compatible API URL:\n\n{url}/v1\n')
+            on_start=lambda url: logger.info(f'API URL (OpenAI + Anthropic compatible):\n\n{url}/v1\n')
         )
     else:
         url_proto = 'https://' if (ssl_certfile and ssl_keyfile) else 'http://'
         urls = [f'{url_proto}{addr}:{port}/v1' for addr in server_addrs]
         if len(urls) > 1:
-            logger.info('OpenAI-compatible API URLs:\n\n' + '\n'.join(urls) + '\n')
+            logger.info('API URLs (OpenAI + Anthropic compatible):\n\n' + '\n'.join(urls) + '\n')
         else:
-            logger.info('OpenAI-compatible API URL:\n\n' + '\n'.join(urls) + '\n')
+            logger.info('API URL (OpenAI + Anthropic compatible):\n\n' + '\n'.join(urls) + '\n')
 
     # Log API keys
     if shared.args.api_key:
diff --git a/modules/api/typing.py b/modules/api/typing.py
index 80831c44..1d486e8f 100644
--- a/modules/api/typing.py
+++ b/modules/api/typing.py
@@ -144,7 +144,7 @@ class CompletionResponse(BaseModel):
 
 
 class ChatCompletionRequestParams(BaseModel):
-    messages: List[dict]
+    messages: List[dict] = Field(..., min_length=1)
     model: str | None = Field(default=None, description="Unused parameter. To change the model, use the /v1/internal/model/load endpoint.")
     frequency_penalty: float | None = shared.args.frequency_penalty
     function_call: str | dict | None = Field(default=None, description="Unused parameter.")
@@ -282,6 +282,25 @@ class LoadLorasRequest(BaseModel):
     lora_names: List[str]
 
 
+class AnthropicRequestParams(BaseModel):
+    model: str | None = None
+    messages: List[dict] = Field(..., min_length=1)
+    max_tokens: int
+    system: str | list | None = None
+    temperature: float | None = shared.args.temperature
+    top_p: float | None = shared.args.top_p
+    stop_sequences: list[str] | None = None
+    stream: bool = False
+    tools: list[dict] | None = None
+    tool_choice: dict | None = None
+    thinking: dict | None = None
+    metadata: dict | None = None
+
+
+class AnthropicRequest(GenerationOptions, AnthropicRequestParams):
+    pass
+
+
 class ImageGenerationRequest(BaseModel):
     """Image-specific parameters for generation."""
     prompt: str