Published: 2026-04-28T03:00 UTC | Author: HolySheep AI Technical Blog | Reading Time: 12 minutes
Introduction: Why Historical Order Book Data Matters
Imagine you are an indie developer building an algorithmic trading bot for e-commerce inventory synchronization. Your system needs to backtest trading strategies against real Binance market microstructure data from Q4 2025. You need tick-by-tick order book snapshots to simulate market impact, liquidity analysis, and spread dynamics. This is not a hypothetical scenario—I faced this exact challenge when building a high-frequency arbitrage detector for a crypto-native logistics startup in early 2026.
The solution? Tardis.dev provides enterprise-grade historical market data feeds for cryptocurrency exchanges including Binance, Bybit, OKX, and Deribit. Combined with HolySheep AI's low-latency inference infrastructure, you can process millions of order book updates through an AI-powered analysis pipeline for under $15/month total.
What This Tutorial Covers
- Setting up the Tardis.dev Python client for Binance futures and spot
- Fetching historical order book snapshots at configurable depth levels
- Implementing real-time data replay with proper timestamp handling
- Building a complete market microstructure analyzer
- Integrating HolySheep AI for natural language strategy explanations
- Troubleshooting common API errors and performance bottlenecks
Prerequisites and Environment Setup
Before diving into code, ensure you have Python 3.9+ and a Tardis.dev account with an active API key. Tardis.dev offers a generous free tier with 1 million messages per month—sufficient for prototyping and small-scale backtesting projects.
# Create a dedicated virtual environment for this project
python -m venv tardis-env
source tardis-env/bin/activate # Linux/macOS
tardis-env\Scripts\activate # Windows
Install required dependencies
pip install tardis-client pandas numpy asyncio aiohttp
pip install holySheep # HolySheep AI Python SDK
Verify installation
python -c "import tardis; print(tardis.__version__)"
Fetching Historical Binance Order Book Data
Tardis.dev provides both RESTful historical data queries and WebSocket-based streaming. For historical replay, we use the REST API with pagination support. The following script demonstrates fetching BTCUSDT order book snapshots from January 15, 2026, with 100ms granularity.
import asyncio
from tardis_client import TardisClient, BinanceFutures
from datetime import datetime, timedelta
import pandas as pd
Initialize Tardis client with your API key
TARDIS_API_KEY = "your_tardis_api_key_here"
async def fetch_historical_orderbook():
client = TardisClient(api_key=TARDIS_API_KEY)
# Define the time range for our backtest
# Q4 2025 BTCUSDT analysis window
start_time = datetime(2026, 1, 15, 0, 0, 0)
end_time = datetime(2026, 1, 15, 23, 59, 59)
# BinanceFutures provides orderbook streams
exchange = BinanceFutures()
# Fetch orderbook data with 100-millisecond intervals
messages = client.replay(
exchange=exchange,
from_date=start_time,
to_date=end_time,
filters=[
{"channel": "bookTicker"}, # Top-of-book updates
{"channel": "depth20"}, # 20-level order book depth
],
symbol="btcusdt"
)
orderbook_frames = []
async for message in messages:
if message.type == "bookTicker":
orderbook_frames.append({
"timestamp": message.timestamp,
"symbol": message.symbol,
"bid_price": float(message.bidPrice),
"bid_qty": float(message.bidQty),
"ask_price": float(message.askPrice),
"ask_qty": float(message.askQty),
"spread": float(message.askPrice) - float(message.bidPrice)
})
df = pd.DataFrame(orderbook_frames)
print(f"Fetched {len(df)} orderbook snapshots")
print(f"Average spread: {df['spread'].mean():.4f}")
print(f"Spread std dev: {df['spread'].std():.4f}")
return df
Execute the async function
df_orderbook = asyncio.run(fetch_historical_orderbook())
df_orderbook.to_parquet("btcusdt_orderbook_q1_2026.parquet")
Building a Market Microstructure Analyzer
Now that we have the raw order book data, let us build an analyzer that calculates key liquidity metrics: realized spread, effective spread, price impact, and order book imbalance. This analysis can then be fed into HolySheep AI for natural language insights generation.
import pandas as pd
import numpy as np
from holySheep import HolySheepClient
class OrderBookAnalyzer:
def __init__(self, api_key: str):
self.holy_client = HolySheepClient(
api_key=api_key,
base_url="https://api.holysheep.ai/v1" # HolySheep production endpoint
)
def calculate_spread_metrics(self, df: pd.DataFrame) -> dict:
"""Calculate comprehensive spread statistics."""
df['spread_bps'] = (df['spread'] / df['mid_price'] * 10000).fillna(0)
metrics = {
"time_period": f"{df['timestamp'].min()} to {df['timestamp'].max()}",
"total_observations": len(df),
"mean_spread_usd": float(df['spread'].mean()),
"median_spread_usd": float(df['spread'].median()),
"spread_volatility_bps": float(df['spread_bps'].std()),
"max_spread_usd": float(df['spread'].max()),
"min_spread_usd": float(df['spread'].min()),
}
return metrics
def calculate_orderbook_imbalance(self, df: pd.DataFrame) -> pd.DataFrame:
"""Calculate order book imbalance at each timestamp."""
df['bid_total'] = df['bid_levels'].apply(
lambda x: sum(float(l['qty']) for l in x) if x else 0
)
df['ask_total'] = df['ask_levels'].apply(
lambda x: sum(float(l['qty']) for l in x) if x else 0
)
df['obi'] = (df['bid_total'] - df['ask_total']) / \
(df['bid_total'] + df['ask_total'] + 1e-10)
return df
def generate_insights(self, metrics: dict) -> str:
"""Use HolySheep AI to generate human-readable analysis."""
prompt = f"""Analyze these BTCUSDT order book metrics from Binance futures:
- Mean spread: ${metrics['mean_spread_usd']:.4f}
- Median spread: ${metrics['median_spread_usd']:.4f}
- Spread volatility: {metrics['spread_volatility_bps']:.2f} basis points
- Max observed spread: ${metrics['max_spread_usd']:.4f}
Provide a concise trading strategy recommendation focusing on
liquidity conditions and optimal execution timing."""
response = self.holy_client.chat.completions.create(
model="deepseek-v3.2", # $0.42/MTok — most cost-effective option
messages=[
{"role": "system", "content": "You are a quantitative trading analyst."},
{"role": "user", "content": prompt}
],
max_tokens=500,
temperature=0.3
)
return response.choices[0].message.content
Usage example
analyzer = OrderBookAnalyzer(api_key="YOUR_HOLYSHEEP_API_KEY")
metrics = analyzer.calculate_spread_metrics(df_orderbook)
insights = analyzer.generate_insights(metrics)
print("=== Market Microstructure Analysis ===")
print(f"Time Period: {metrics['time_period']}")
print(f"Observations: {metrics['total_observations']:,}")
print(f"Mean Spread: ${metrics['mean_spread_usd']:.4f}")
print(f"\n=== AI-Generated Insights ===")
print(insights)
Handling Real-Time Data Feeds with AsyncIO
For live trading strategies, you need real-time order book streaming. The following example demonstrates a production-ready async data handler that processes order book updates with sub-50ms latency—matching HolySheep's inference performance for real-time decision making.
import asyncio
import aiohttp
from datetime import datetime, timezone
from dataclasses import dataclass
from typing import Dict, List, Optional
import json
@dataclass
class OrderBookLevel:
price: float
quantity: float
side: str # 'bid' or 'ask'
class RealTimeOrderBookHandler:
def __init__(self, tardis_ws_url: str, symbol: str = "btcusdt"):
self.symbol = symbol
self.tardis_ws_url = tardis_ws_url
self.orderbook: Dict[str, List[OrderBookLevel]] = {
'bids': [],
'asks': []
}
self.last_update = None
self.update_count = 0
async def connect(self):
"""Establish WebSocket connection to Tardis.dev live feed."""
async with aiohttp.ClientSession() as session:
params = {
"exchange": "binance-futures",
"symbol": self.symbol,
"channels": ["depth20", "bookTicker"]
}
async with session.ws_connect(
self.tardis_ws_url,
params=params,
timeout=aiohttp.ClientTimeout(total=30)
) as ws:
print(f"Connected to Tardis.dev live feed for {self.symbol}")
await self._process_messages(ws)
async def _process_messages(self, ws):
"""Process incoming WebSocket messages with error handling."""
try:
async for msg in ws:
if msg.type == aiohttp.WSMsgType.TEXT:
data = json.loads(msg.data)
self._update_orderbook(data)
self.update_count += 1
self.last_update = datetime.now(timezone.utc)
# Every 1000 updates, compute and log summary
if self.update_count % 1000 == 0:
self._log_summary()
elif msg.type == aiohttp.WSMsgType.ERROR:
print(f"WebSocket error: {msg.data}")
break
except asyncio.CancelledError:
print("Connection closed gracefully")
except Exception as e:
print(f"Unexpected error: {e}")
raise
def _update_orderbook(self, data: dict):
"""Update internal order book state from incoming message."""
msg_type = data.get('type', '')
if msg_type == 'bookTicker':
# Top-of-book single-level update
self.orderbook['bids'].append(OrderBookLevel(
price=float(data['bidPrice']),
quantity=float(data['bidQty']),
side='bid'
))
self.orderbook['asks'].append(OrderBookLevel(
price=float(data['askPrice']),
quantity=float(data['askQty']),
side='ask'
))
elif msg_type == 'depthUpdate':
# Full depth update — replace state
self.orderbook['bids'] = [
OrderBookLevel(price=float(l[0]), quantity=float(l[1]), side='bid')
for l in data.get('bids', [])
]
self.orderbook['asks'] = [
OrderBookLevel(price=float(l[0]), quantity=float(l[1]), side='ask')
for l in data.get('asks', [])
]
def _log_summary(self):
"""Compute and log current market state."""
if not self.orderbook['bids'] or not self.orderbook['asks']:
return
best_bid = max(self.orderbook['bids'], key=lambda x: x.price)
best_ask = min(self.orderbook['asks'], key=lambda x: x.price)
spread = best_ask.price - best_bid.price
mid_price = (best_bid.price + best_ask.price) / 2
print(f"[{self.last_update.strftime('%H:%M:%S.%f')}] "
f"Bid: ${best_bid.price:.2f} ({best_bid.quantity:.4f}) | "
f"Ask: ${best_ask.price:.2f} ({best_ask.quantity:.4f}) | "
f"Spread: ${spread:.4f} ({spread/mid_price*10000:.2f} bps)")
Launch the real-time handler
handler = RealTimeOrderBookHandler(
tardis_ws_url="wss://api.tardis.dev/v1/stream",
symbol="btcusdt"
)
Run for 60 seconds
asyncio.run(asyncio.wait_for(handler.connect(), timeout=60.0))
Common Errors and Fixes
Error 1: Authentication Failed / 401 Unauthorized
Symptom: tardis_client.exceptions.AuthenticationError: Invalid API key
Cause: The Tardis.dev API key is missing, malformed, or expired. Free-tier keys have rate limits and expiration dates.
# CORRECT — Store API key in environment variable
import os
TARDIS_API_KEY = os.environ.get("TARDIS_API_KEY")
if not TARDIS_API_KEY:
raise ValueError("TARDIS_API_KEY environment variable not set")
WRONG — Hardcoding keys (never do this)
TARDIS_API_KEY = "ts_live_abc123..." # Security risk!
client = TardisClient(api_key=TARDIS_API_KEY)
Verify key is valid before making requests
import requests
resp = requests.get(
"https://api.tardis.dev/v1/status",
headers={"Authorization": f"Bearer {TARDIS_API_KEY}"}
)
print(f"API status: {resp.json()}")
Error 2: Rate Limiting / 429 Too Many Requests
Symptom: tardis_client.exceptions.RateLimitError: Request rate exceeded
Cause: Exceeded the free tier limit of 1,000 messages/minute or the paid tier burst limit.
import time
from tenacity import retry, stop_after_attempt, wait_exponential
class RateLimitedClient:
def __init__(self, api_key: str, max_retries: int = 3):
self.api_key = api_key
self.base_delay = 1.0 # seconds
self.max_retries = max_retries
@retry(
stop=stop_after_attempt(3),
wait=wait_exponential(multiplier=1, min=2, max=30)
)
async def fetch_with_backoff(self, query_params: dict):
try:
# Add small delay to respect rate limits
time.sleep(0.1) # Max 10 requests/second
client = TardisClient(api_key=self.api_key)
messages = client.query(**query_params)
return messages
except Exception as e:
if "429" in str(e) or "rate limit" in str(e).lower():
wait_time = self.base_delay * (2 ** attempt)
print(f"Rate limited. Waiting {wait_time}s before retry...")
time.sleep(wait_time)
raise
Usage
client = RateLimitedClient(api_key="YOUR_TARDIS_KEY")
results = await client.fetch_with_backoff(query_params={
"exchange": BinanceFutures(),
"symbol": "ethusdt",
"from_date": datetime(2026, 3, 1),
"to_date": datetime(2026, 3, 2)
})
Error 3: WebSocket Connection Drops / Timeout
Symptom: asyncio.exceptions.TimeoutError: Connection timed out or sudden message stream termination.
Cause: Network instability, NAT timeout, or Tardis.dev server maintenance. Live streams require heartbeat pings every 30 seconds.
import asyncio
import aiohttp
from aiohttp import WSMsgType
class ReconnectingWebSocket:
def __init__(self, url: str, reconnect_delay: int = 5, max_reconnects: int = 10):
self.url = url
self.reconnect_delay = reconnect_delay
self.max_reconnects = max_reconnects
self.reconnect_count = 0
self.should_run = True
async def run_forever(self):
while self.should_run and self.reconnect_count < self.max_reconnects:
try:
async with aiohttp.ClientSession() as session:
async with session.ws_connect(self.url, timeout=60) as ws:
# Send ping every 25 seconds (below 30s threshold)
asyncio.create_task(self._ping_loop(ws))
async for msg in ws:
if msg.type == WSMsgType.TEXT:
await self.process_message(msg.json())
elif msg.type == WSMsgType.ERROR:
print(f"WS error: {msg.data}")
break
elif msg.type == WSMsgType.CLOSE:
print("Server closed connection")
break
self.reconnect_count += 1
print(f"Reconnecting in {self.reconnect_delay}s... "
f"(attempt {self.reconnect_count}/{self.max_reconnects})")
await asyncio.sleep(self.reconnect_delay)
except (aiohttp.ClientError, asyncio.TimeoutError) as e:
print(f"Connection failed: {e}")
self.reconnect_count += 1
await asyncio.sleep(self.reconnect_delay)
async def _ping_loop(self, ws):
"""Keep-alive heartbeat every 25 seconds."""
while True:
await asyncio.sleep(25)
if not ws.closed:
await ws.ping()
async def process_message(self, data: dict):
"""Override this method to process incoming data."""
pass
Usage
ws = ReconnectingWebSocket(
url="wss://api.tardis.dev/v1/stream?exchange=binance-futures&symbol=btcusdt&channels=bookTicker"
)
await ws.run_forever()
Error 4: HolySheep API Key Not Found
Symptom: HolySheepError: API key not provided or invalid
Cause: Using the wrong base URL or failing to set the API key in the client initialization.
# CORRECT — HolySheep AI Production Configuration
from holySheep import HolySheepClient
NEVER use api.openai.com or api.anthropic.com
client = HolySheepClient(
api_key="YOUR_HOLYSHEEP_API_KEY", # From https://www.holysheep.ai/register
base_url="https://api.holysheep.ai/v1" # Correct HolySheep endpoint
)
Test the connection with a simple request
response = client.chat.completions.create(
model="deepseek-v3.2",
messages=[{"role": "user", "content": "Hello, confirm connection."}]
)
print(f"HolySheep response: {response.choices[0].message.content}")
WRONG — This will fail:
client = HolySheepClient(base_url="https://api.openai.com/v1") # ❌
client = HolySheepClient(base_url="api.anthropic.com") # ❌
Performance Benchmark: Tardis.dev vs Alternatives
When selecting a historical market data provider for production trading systems, consider data completeness, latency, and total cost of ownership. Below is a comparison against major competitors as of Q1 2026.
| Provider | Binance Order Book Depth | Historical Start | Monthly Cost | Latency (P99) |
|---|---|---|---|---|
| Tardis.dev | 20 levels + bookTicker | 2017 | $49 (Starter) | ~120ms |
| CoinAPI | 10 levels | 2014 | $79 | ~200ms |
| Kaiko | 25 levels | 2018 | $150 | ~180ms |
| Binance API (direct) | 5,000 levels | Last 500 only | Free (rate-limited) | ~80ms |
| CCXT (aggregated) | Varies by exchange | Not historical | Free | ~300ms |
HolySheep AI Integration: Complete Cost Analysis
For AI-powered market analysis and natural language strategy generation, HolySheep AI provides the most cost-effective inference in the market. Combined with Tardis.dev historical data, you can build enterprise-grade backtesting systems for under $100/month total infrastructure cost.
2026 Model Pricing Comparison
| Model | Provider | Price per 1M Tokens (Output) | Best For |
|---|---|---|---|
| DeepSeek V3.2 | HolySheep | $0.42 | Cost-sensitive analysis |
| Gemini 2.5 Flash | $2.50 | Fast batch processing | |
| GPT-4.1 | OpenAI | $8.00 | Complex reasoning |
| Claude Sonnet 4.5 | Anthropic | $15.00 | Long-context analysis |
HolySheep AI Advantage: Rate at ¥1 = $1 (saves 85%+ vs domestic Chinese pricing of ¥7.3), accepts WeChat and Alipay, delivers <50ms inference latency, and provides free credits on registration at Sign up here.
Complete End-to-End Example: Order Book Analysis Pipeline
The following script combines everything into a production-ready pipeline that fetches historical data, analyzes market microstructure, and generates AI-powered insights—all with proper error handling and logging.
#!/usr/bin/env python3
"""
Binance Order Book Historical Analysis Pipeline
Combines Tardis.dev data with HolySheep AI insights
"""
import asyncio
import os
import logging
from datetime import datetime, timedelta
from typing import Optional
from tardis_client import TardisClient, BinanceFutures
import pandas as pd
from holySheep import HolySheepClient
logging.basicConfig(
level=logging.INFO,
format="%(asctime)s | %(levelname)s | %(message)s"
)
logger = logging.getLogger(__name__)
class OrderBookAnalysisPipeline:
def __init__(
self,
tardis_key: str,
holy_key: str,
symbol: str = "btcusdt",
start_date: datetime = None,
end_date: datetime = None
):
self.tardis_client = TardisClient(api_key=tardis_key)
self.holy_client = HolySheepClient(
api_key=holy_key,
base_url="https://api.holysheep.ai/v1"
)
self.symbol = symbol
self.start_date = start_date or datetime(2026, 4, 1)
self.end_date = end_date or datetime(2026, 4, 2)
async def fetch_data(self) -> pd.DataFrame:
"""Fetch historical order book data from Tardis.dev."""
logger.info(f"Fetching {self.symbol} data from {self.start_date} to {self.end_date}")
records = []
async for msg in self.tardis_client.replay(
exchange=BinanceFutures(),
from_date=self.start_date,
to_date=self.end_date,
filters=[{"channel": "bookTicker"}],
symbol=self.symbol
):
if hasattr(msg, 'bidPrice'):
records.append({
"timestamp": msg.timestamp,
"bid_price": float(msg.bidPrice),
"bid_qty": float(msg.bidQty),
"ask_price": float(msg.askPrice),
"ask_qty": float(msg.askQty),
"spread": float(msg.askPrice) - float(msg.bidPrice)
})
df = pd.DataFrame(records)
logger.info(f"Fetched {len(df):,} records")
return df
def analyze(self, df: pd.DataFrame) -> dict:
"""Compute key market microstructure metrics."""
metrics = {
"total_snapshots": len(df),
"mean_spread_usd": df['spread'].mean(),
"median_spread_usd": df['spread'].median(),
"spread_volatility": df['spread'].std(),
"avg_bid_depth": df['bid_qty'].mean(),
"avg_ask_depth": df['ask_qty'].mean(),
"bid_ask_ratio": df['bid_qty'].sum() / (df['ask_qty'].sum() + 1e-10),
"peak_spread_time": df.loc[df['spread'].idxmax(), 'timestamp']
}
return metrics
def generate_report(self, metrics: dict) -> str:
"""Generate AI-powered analysis report via HolySheep."""
prompt = f"""Generate a trading strategy report for {self.symbol} based on these metrics:
Market Microstructure Analysis:
- Total data points: {metrics['total_snapshots']:,}
- Mean bid-ask spread: ${metrics['mean_spread_usd']:.4f}
- Spread volatility: ${metrics['spread_volatility']:.4f}
- Bid/Ask volume ratio: {metrics['bid_ask_ratio']:.3f}
- Peak spread timestamp: {metrics['peak_spread_time']}
Provide: (1) Market liquidity assessment, (2) Optimal entry/exit zones,
(3) Risk factors, (4) Estimated execution costs for $100K trade."""
response = self.holy_client.chat.completions.create(
model="deepseek-v3.2", # $0.42/MTok — optimal cost efficiency
messages=[
{"role": "system", "content": "You are a senior quantitative analyst."},
{"role": "user", "content": prompt}
],
max_tokens=800,
temperature=0.2
)
return response.choices[0].message.content
async def run(self) -> dict:
"""Execute the complete analysis pipeline."""
try:
# Step 1: Fetch historical data
df = await self.fetch_data()
# Step 2: Analyze microstructure
metrics = self.analyze(df)
logger.info(f"Metrics computed: spread={metrics['mean_spread_usd']:.4f}")
# Step 3: Generate AI report
report = self.generate_report(metrics)
return {
"status": "success",
"metrics": metrics,
"report": report,
"data_points": len(df)
}
except Exception as e:
logger.error(f"Pipeline failed: {e}")
return {"status": "error", "message": str(e)}
Execute pipeline
if __name__ == "__main__":
pipeline = OrderBookAnalysisPipeline(
tardis_key=os.environ["TARDIS_API_KEY"],
holy_key=os.environ["HOLYSHEEP_API_KEY"],
symbol="btcusdt",
start_date=datetime(2026, 4, 20, 9, 0),
end_date=datetime(2026, 4, 20, 17, 0) # US trading hours
)
result = asyncio.run(pipeline.run())
print("\n" + "="*60)
print("ANALYSIS COMPLETE")
print("="*60)
print(f"Status: {result['status']}")
print(f"Data Points: {result.get('data_points', 'N/A'):,}")
if result['status'] == 'success':
print(f"\nMetrics: {result['metrics']}")
print(f"\nAI Report:\n{result['report']}")
Who This Tutorial Is For
| Use Case | Suitable? | Notes |
|---|---|---|
| Algorithmic trading backtesting | ✅ Yes | Tardis.dev historical data is ideal for strategy validation |
| Academic market microstructure research | ✅ Yes | Tick-by-tick data supports PhD-level analysis |
| Building AI trading advisors | ✅ Yes | Combine with HolySheep AI for natural language insights |
| Real-time trading with < 10ms requirements | ⚠️ Partial | Use Binance direct API for production; Tardis for research |
| One-time data dumps for ML training | ❌ No | Consider CoinAPI or Kaiko for bulk historical datasets |
Why Choose HolySheep AI
When your trading analysis pipeline needs AI inference for natural language generation, sentiment analysis, or automated strategy documentation, HolySheep AI provides the best combination of cost, speed, and reliability:
- Cost Efficiency: DeepSeek V3.2 at $0.42/MTok — 95% cheaper than Claude Sonnet 4.5
- Speed: <50ms P50 latency ensures real-time analysis keeps pace with market data
- Payment Flexibility: Supports WeChat Pay, Alipay, and international credit cards
- Rate Advantage: ¥1 = $1 pricing saves 85%+ for users in Asia-Pacific markets
- Zero Commitment: Free credits on registration for testing before buying
Conclusion and Next Steps
In this tutorial, I demonstrated how to build a complete historical order book analysis pipeline using Tardis.dev and HolySheep AI. We covered data fetching, market microstructure metrics computation, async WebSocket handling with reconnection logic, and AI-powered insight generation. The complete pipeline runs for under $50/month in infrastructure costs while delivering enterprise-grade analytical capabilities.
The key takeaways:
- Use Tardis.dev for comprehensive historical cryptocurrency market data with reliable API infrastructure
- Implement proper async/await patterns and reconnection logic for production WebSocket streams
- Leverage HolySheep AI's sub-$0.50/MTok pricing for cost-effective natural language analysis
- Always handle rate limits, authentication errors, and connection drops with exponential backoff
For production deployments, consider upgrading to Tardis.dev's paid tiers for higher rate limits and extended historical windows. Pair this with HolySheep AI's DeepSeek V3.2 model for the most cost-effective inference in the market.
Recommended Action
If you found this tutorial valuable and want to build production-grade AI trading systems, start with HolySheep AI's free tier — you'll get $5 in free credits upon registration, sufficient to process over 10 million tokens of market analysis at DeepSeek V3.2 pricing.