LLM API integration is the process of connecting applications to large language model providers through standardized interfaces, enabling developers to leverage AI capabilities without managing infrastructure. The 2026 provider landscape spans OpenAI's GPT-5.4 family, Anthropic Claude 4.6, Google Gemini 2.5/3.1, and cost-disruptive options like DeepSeek V4 (5–10× cheaper than frontier models) and Amazon Bedrock's unified multi-model API—nearly all offering OpenAI-compatible endpoints. The Model Context Protocol (MCP) has become the de facto tool connectivity standard, while first-party agent SDKs (OpenAI Agents SDK, Claude Agent SDK, Google ADK) have made stateful multi-step agentic workflows production-grade. The key challenge lies not in calling a single API, but in building resilient, observable, and cost-effective systems that handle rate limits, fallbacks, context management, multi-provider routing, and LLM-specific security threats such as prompt injection—skills that separate prototype AI apps from production-grade deployments.
What This Cheat Sheet Covers
This topic spans 14 focused tables and 151 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
Table 1: Major LLM API Providers
Knowing each provider's flagship models, pricing tier, and authentication style is the first step before writing a single line of integration code. Pricing and model names change frequently; check provider dashboards before committing architecture decisions.
| Provider | Example | Description |
|---|---|---|
base_url="https://api.openai.com/v1"model="gpt-5.4" | • Flagship: GPT-5.4, GPT-5.3 Instant, GPT-5-mini • ~ 1.25/10 per M tokens• de facto industry standard • Responses API replaces Assistants API for agentic workflows | |
base_url="https://api.anthropic.com"model="claude-opus-4-6" | • Flagship: Claude Opus 4.6, Sonnet 4.6, Haiku 4.5 • ~ 5/25 per M (Opus)• extended thinking, computer use, MCP, and subagents built-in • strong safety profile | |
base_url="https://generativelanguage.googleapis.com"model="gemini-2.5-pro" | • Flagship: Gemini 2.5 Pro (GA), Gemini 2.5 Flash, Gemini 3.1 Pro (preview) • 1M+ token context • grounding via Google Search • multimodal (text, image, audio, video) | |
base_url="https://{resource}.openai.azure.com/openai/deployments/{deployment}" | • Hosts GPT-5.4 and latest OpenAI models • enterprise compliance (SOC 2, HIPAA, GDPR) • private networking • same OpenAI SDK with resource-specific endpoint | |
client = boto3.client("bedrock-runtime")model_id="anthropic.claude-sonnet-4-6" | • Unified API for Claude, Llama 3.3, Mistral, Titan, DeepSeek R1 • IAM auth • no per-model API keys • serverless pay-per-token • GuardRails, Agents, Knowledge Bases built-in | |
base_url="https://api.x.ai/v1"model="grok-4-1-fast" | • Grok 4 ( 3/15/M), Grok 4.1 Fast (2M context, 0.20/0.50/M)• real-time X/Twitter data access • OpenAI-compatible | |
base_url="https://api.mistral.ai/v1"model="mistral-large-3" | • Mistral Large 3, Medium 3, Codestral • EU-hosted option • function calling, vision • strong European data-residency story |