feat(deepseek): beta Support strict Mode

[ishahroz]

Description: This PR adds support for DeepSeek's beta strict mode feature for structured
outputs and tool calling. It overrides bind_tools() and with_structured_output() to automatically use
DeepSeek's beta endpoint (https://api.deepseek.com/beta) when strict=True. Both methods need overriding because they're independent entry points and user can call either directly. When DeepSeek's strict mode graduates from beta, we can just remove both overriden methods. You can read more about the beta feature here: https://api-docs.deepseek.com/guides/function_calling#strict-mode-beta

Issue: Implements #32670

Dependencies: None

Sample Code

from langchain_deepseek import ChatDeepSeek
from pydantic import BaseModel, Field
from typing import Optional
import os


# Enter your DeepSeek API Key here
API_KEY = "YOUR_API_KEY"


# location, temperature, condition are required fields
# humidity is optional field with default value
class WeatherInfo(BaseModel):
    location: str = Field(description="City name")
    temperature: int = Field(description="Temperature in Celsius")
    condition: str = Field(description="Weather condition (sunny, cloudy, rainy)")
    humidity: Optional[int] = Field(default=None, description="Humidity percentage")


llm = ChatDeepSeek(
    model="deepseek-chat",
    api_key=API_KEY,
)

# just to confirm that a new instance will use the default base url (instead of beta)
print(f"Default API base: {llm.api_base}")



# Test 1: bind_tools with strict=True shoud list all the tools calls
print("\nTest 1: bind_tools with strict=True")
llm_with_tools = llm.bind_tools([WeatherInfo], strict=True)
response = llm_with_tools.invoke("Tell me the weather in New York. It's 22 degrees, sunny.")
print(response.tool_calls)



# Test 2: with_structured_output with strict=True
print("\nTest 2: with_structured_output with strict=True")
structured_llm = llm.with_structured_output(WeatherInfo, strict=True)
result = structured_llm.invoke("Tell me the weather in New York.")
print(f"  Result: {result}")
assert isinstance(result, WeatherInfo), "Result should be a WeatherInfo instance"

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
langchain	Ignored	Preview		Aug 27, 2025 11:39pm

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #32727 will not alter performance

_{Comparing ishahroz:feat/deepseek-strict-mode-beta-support (5831da0) with master (7f9b077)}

⚠️ Unknown Walltime execution environment detected

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Summary

✅ 13 untouched benchmarks

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #32727 will not alter performance

_{Comparing ishahroz:feat/deepseek-strict-mode-beta-support (5831da0) with master (7f9b077)}

Summary

✅ 14 untouched benchmarks