docs: document multi-provider LLM support via litellm

README and quickstart now show that the system works with any
litellm-compatible LLM provider (OpenAI, Azure, Bedrock, Cohere, Ollama,
Vertex AI, etc.), not just Anthropic.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mobtownlabs

.beads/PROGRESS.md

@@ -42,4 +42,4 @@
 | \[ ] | buyer-j95 | 3G: Infrastructure-as-Code Deployment (CloudFormation/Terraform) | P3 | — |  |
 
 ---
-*Last updated: 2026-03-10 21:44 UTC — auto-generated by beads*
+*Last updated: 2026-03-10 22:00 UTC — auto-generated by beads*

README.md

@@ -137,7 +137,15 @@ cp .env.example .env
 Key settings:
 
 ```bash
-ANTHROPIC_API_KEY=sk-ant-api03-xxxxx        # Required
+# LLM — set the API key for your chosen provider
+ANTHROPIC_API_KEY=sk-ant-api03-xxxxx        # For Anthropic (default)
+# OPENAI_API_KEY=sk-xxxxx                   # For OpenAI / Azure
+# COHERE_API_KEY=xxxxx                      # For Cohere
+
+# LLM model (uses litellm provider/model format — any provider works)
+DEFAULT_LLM_MODEL=anthropic/claude-sonnet-4-5-20250929
+# DEFAULT_LLM_MODEL=openai/gpt-4o          # OpenAI example
+# DEFAULT_LLM_MODEL=ollama/llama3           # Local Ollama example
 
 # Seller connection
 SELLER_BASE_URL=http://localhost:8001        # Seller agent URL
@@ -146,6 +154,8 @@ SELLER_BASE_URL=http://localhost:8001        # Seller agent URL
 DATABASE_URL=sqlite:///./ad_buyer.db
 ```
 
+> **LLM Provider Flexibility:** The agent uses [litellm](https://docs.litellm.ai/) under the hood, supporting 100+ LLM providers (OpenAI, Azure, Cohere, Ollama, Vertex AI, Bedrock, etc.). Set `DEFAULT_LLM_MODEL` and `MANAGER_LLM_MODEL` using `provider/model-name` format and provide the matching API key. See the [Quickstart Guide](https://iabtechlab.github.io/buyer-agent/getting-started/quickstart/) for details.
+
 → [Full Configuration](https://iabtechlab.github.io/buyer-agent/getting-started/quickstart/)
 
 ### Run

docs/getting-started/quickstart.md

@@ -27,8 +27,10 @@ pip install -e .
 Create a `.env` file in the project root:
 
 ```dotenv
-# LLM
-ANTHROPIC_API_KEY=sk-ant-...
+# LLM — set the API key for your chosen provider
+ANTHROPIC_API_KEY=sk-ant-...              # For Anthropic (default)
+# OPENAI_API_KEY=sk-xxxxx                 # For OpenAI / Azure
+# COHERE_API_KEY=xxxxx                    # For Cohere
 
 # Inbound API key for this service (leave empty to disable auth in dev)
 API_KEY=
@@ -41,9 +43,11 @@ OPENDIRECT_API_KEY=            # API key for seller (optional)
 # Multi-seller mode (comma-separated URLs)
 SELLER_ENDPOINTS=
 
-# LLM model overrides (defaults shown)
+# LLM model overrides — uses litellm provider/model format (any provider works)
 DEFAULT_LLM_MODEL=anthropic/claude-sonnet-4-5-20250929
 MANAGER_LLM_MODEL=anthropic/claude-opus-4-20250514
+# DEFAULT_LLM_MODEL=openai/gpt-4o         # OpenAI example
+# DEFAULT_LLM_MODEL=ollama/llama3          # Local Ollama example
 
 # Environment
 ENVIRONMENT=development
@@ -52,6 +56,9 @@ LOG_LEVEL=INFO
 
 All settings are loaded from environment variables or the `.env` file via `pydantic-settings`.
 
+!!! info "LLM Provider Flexibility"
+    The buyer agent uses [litellm](https://docs.litellm.ai/) under the hood, supporting **100+ LLM providers** — OpenAI, Azure, Cohere, Ollama, Vertex AI, Bedrock, and more. Set `DEFAULT_LLM_MODEL` and `MANAGER_LLM_MODEL` using `provider/model-name` format and provide the matching API key environment variable. Agent prompts are tuned for Claude but work with any capable model. See the [litellm provider docs](https://docs.litellm.ai/docs/providers) for the full list.
+
 ## Run the Server
 
 ```bash